Sciurus bibliography.doc

Annotated Bibliography on the
Ecology and Management of Invasive Species:
Eastern Grey Squirrel (Sciurus carolinensis)
Prepared by Carrina Maslovat, Victoria British Columbia For the Garry Oak Ecosystems Recovery Team Funding supplied by the Habitat Stewardship Program of the Government of Canada January, 2003

Applied Vegetation Dynamics.
2000. Fact sheet: TA/M/13. Invasive Alien Terrestrial
Animal Species Sciurus carolinensis (Gmelin, 1788.) - Grey Squirrel.
Accessed: November 20, 2002.
The website is maintained by a research unit based at the University of Liverpool that
aims to provide information on the ecology and management of invasive species in the
United Kingdom. The site provides species descriptions, life history details, range
information as well as discussing the impacts and potential control measures of eastern
grey squirrels. Eastern grey squirrels were introduced to Britain in the late 19th century
and now cause major damage to ecosystems. They gnaw the bark of trees which kills or
slows the growth of the trees. Squirrels remove the bark 30 cm above the ground. Grey
squirrels also impact European red squirrels through competition and by possibly acting
as a vector for the disease parapoxvirus. Grey squirrels are found primarily in deciduous
woodlands but also occurs in coniferous and mixed stands. Although the red squirrel is a
different species from the native red squirrel in British Columbia, the potential impacts
may be similar although this requires further research. The best control options for grey
squirrels include the use of Warfarin (rodenticide) in specialized hoppers (used only
where there are no red squirrels) and cage trapping in conjunction with shooting. These
techniques may also be useful Garry oak ecosystems. However, new individuals from
adjacent populations will rapidly repopulate an area and total eradication is unlikely.
Baits can be used to lure squirrels away from sensitive sites. Immuno-contraception
methods require more research before they can be implemented.

Banfield, A. W. F.
1974. The Mammals of Canada. University of Toronto, Toronto,

This comprehensive field guide provides detailed species description and life history
information. The dated range map does not show the introduction of grey squirrels to
Vancouver Island. Eastern grey squirrels are described as tree squirrels with a long flat
tails. Grey squirrels have lighter undersides, brown faces feet and flanks and white tipped
brownish tails. There are also black and red forms of the same species. Grey squirrels are
described as "socially tolerant" and individuals may feed or den together. Grey squirrels
will give up territory to the more territorial native red squirrels however they can
outnumber red squirrels and are not prevented from feeding in the red's territory. Peak
activity is between 7 and 8 am and also between 3 and 6 pm. Grey squirrels nest in
cavities or loosely woven dreys in conifers or large deciduous trees. Historically, grey
squirrels are known to undergo mass emigrations to new areas for unknown reasons that
are not related to food shortages. Grey squirrels feed on buds of deciduous trees, flowers,
seeds, fruits, insects, birds' eggs and hard nuts that are cached for the winter. Grey
squirrels are found in hardwood or mixed forests as well as urban and suburban habitats.
Detailed reproductive biology is outlined in this reference including the habit of two
breeding seasons, breeding rituals, number of litters (average of 1.4/year), gestation (45
days), number in litter (4-6) and development of the young. The ecology of the grey
squirrel gives important background for potential management options in Garry oak

Barthelmess, E. L
. 2001. The effects of tannin and protein on food preference in
eastern grey squirrels. Ethology Ecology and Evolution 13 (2): 115-132.
Author's abstract: Although some mammalian generalist herbivores avoid foods high in
plant secondary compounds, it has not been adequately shown that eastern grey squirrels
(Sciurus carolinensis), who regularly encounter tannin in acorns, avoid high tannin diets.
Dietary tannin can inhibit nitrogen assimilation; hence herbivores that eat tannin should
seek high protein diets to compensate. I presented free-ranging grey squirrels with four
types of dough balls that differed in tannin and protein content. Squirrels consistently
preferred low to high tannin foods but did not distinguish between low and high protein
foods. Intensity of preference for low tannin foods was greatest during early to mid
autumn, when food is relatively abundant, and declined into the spring and early summer,
when food is relatively scarce. Food availability, partitioning foraging effort between
eating and scatterhoarding, physiological competence, and nutrient complementarity may
explain why squirrels consume tannin in natural diets, in spite of preference for low
tannin dough balls demonstrated here.
Bloemacher, S. (Aliens-L listserve) 2002. Translation of German Grey Squirrel Fact
Sheet. Website:
In Germany, eastern grey squirrels are found only in captivity although there are
unconfirmed sightings in the wild. Grey squirrels have caused serious problems in other
locations in Europe by competing with European red squirrels (Sciurus vulgaris) for food
and habitat, damaging gardens, stripping tree bark, competing with birds for food and
destroying bird nests. Grey squirrels also try to mate with European red squirrels
although no viable hybrids have been observed. All efforts should be made to prevent the
release of grey squirrels to the wild in Germany.
Bowers, M. A. and B. Breland. 1996. Foraging of gray squirrels on an urban-rural
gradient: Use of the gud to assess anthropogenic impact. Ecological Applications 6 (4):
Authors' abstract: Responses of organisms to urbanization may involve adjustments in
behavior. To qualify such behavioral plasticity we measured the degree to which gray
squirrels (Sciurus carolinensis) exploited sunflower seeds in pans distributed over an
urban-rural gradient of 78 sites in Virginia. Our objective was to use squirrel GUDs as a
functional, relativistic measure of the effects of urbanization. Results showed that a
higher proportion of pans were foraged from and that the GUDs were lower (more seeds
were removed) in relatively high-density urban and suburban areas than in more rural
agricultural areas, or in relatively human- free forest controls. For sites near or within
human settlements, GUDs were lower nearer to human-occupied structures than at a
greater distance from them, where more squirrels were observed, and where the density
of trees was higher; GUDs were higher where there was substantial ground cover and
where domestic pets (i.e., cats/dogs) were present nearby. Squirrels living in close
proximity to humans appear to be either more limited by food or less sensitive to
predatory risk than those living in more natural areas. We argue that the GUD represents
a valuable metric with utility for measuring the separate and combined impact of
anthropogenic actions at the individual and population levels.
Brenner, F. J. and T. Johnson. 1989. Use of habitat suitability index HSI models to
evaluate fox and gray squirrel habitat in western Pennsylvania, USA. Journal of the
Pennsylvania Academy of Science 63 (2): 77-80.
Authors' abstract: The Habitat Suitability Index (HSI) model was used to evaluate fox
(Sciurus niger) and gray squirrel (S. carolinensis) habitat on four woodlots in Western
Pennsylvania. Two woodlots were inhabited by both species while only gray squirrels
were observed on the other two areas. The cover/reproduction component of HSI appears
to be more important than winter food in determining the suitability of habitat for fox
squirrels. With a decline in fox squirrels, there is a corresponding increase in the number
of gray squirrels inhabiting the woodlots. The presence of agricultural land in close
proximity to the woodlot appears to be an important factor in determining whether or not
the area will be inhabited by fox squirrels, whereas the presence of den trees in an
important component of gray squirrel habitat.

Brown, B. W. and G. O. Batzli
. 1985. Field manipulations of fox squirrel Sciurus
and gray squirrel Sciurus carolinensis populations. How important is interspecific
competition? Canadian Journal of Zoology 63 (9): 2134-2140.
Authors' abstract: The role of competition in free-living populations of tree squirrels was
evaluated in two field experiments. (i) Numbers of adult female fox squirrels (Sciurus
) were manipulated and the response of gray squirrels (Sciurus carolinensis) was
monitored. (ii) Supplemental feeding with native mast was used to determine if food was
limiting for squirrel populations in east-central Illinois [USA]. Although sample sizes
were small, a trend towards increased survival and reproduction in supplemented
woodlots lent support to the idea that food availability limits squirrel densities during
some winters. The manipulation of adult female fox squirrels did not indicate that
densities of either fox or gray squirrels could be explained simply by competition. Some
dispersion patterns on the larger plots were consistent with competition, but other
explanations could not be completely ruled out.
Bruemmer, C., P. Lurz, K. Larsen and J. Gurnell, 2000. Impacts and management of
the alien eastern gray squirrel in Great Britain and Italy: lessons for British Columbia.
Pp. 341-349 in: Proceedings of a conference on the biology and management of species
and habitats at risk, Kamloops, British Columbia, 15-19 Feb., 1999 (L. Darling, ed).
Ministry of Environment, Lands and Parks, Victoria, BC.
Bruemmer et al. outline the impacts and history of grey squirrels’ introduction to
England. The authors use this information to identify possible impacts of the introduction
of grey squirrels to similar habitat in Garry oak ecosystems. Grey squirrels were first
introduced to Britain in 1876 and there was a long time lag before they began to spread
quickly through England, Wales and Scotland. The introduction of grey squirrels to
Vancouver Island also exhibited a lag time before the squirrels began to spread
throughout southern Vancouver Island from Sooke to Swartz Bay to Nanaimo. In
England, grey squirrels cause serious environmental problems throughout their new
habitat. European red squirrels (Sciurus vulgaris) are now extinct in most of southern
England probably due to competition with grey squirrels for food and habitat. Grey
squirrels in their native range are closely associated with hardwood forests including oaks
and may digest acorns more efficiently than red squirrels. European red squirrels are
more closely associated with conifer forests but previously inhabited woodlands before
grey squirrels were introduced. Grey squirrels may also infect red squirrels by acting as a
vector for parapoxvirus. Red squirrels native to Garry oak ecosystems in British
Columbia, are conifer dwelling like European red squirrels. Native red squirrels may also
be outnumbered by grey squirrels adapted to deciduous forests and be infected by
diseases carried by grey squirrels. Although British Columbia's red squirrels are highly
territorial in conifer stands, when the squirrels inhabit deciduous forests, their home
ranges overlap and they do not defend their territories. Grey squirrels impact timber
production in England by removing bark from either the base of the trunk, stem or crown
of the tree and making trees more susceptible to infections. Bruemmer et al. suggests
grey squirrels may have a similar impact in Garry oak ecosystems although further
research is needed to support this. In England, grey squirrels impact the natural
regeneratio n of oaks by biting out the radicles and preventing oak germination. Notched
acorns have also been observed in Garry oak ecosystems. Although other authors believe
the squirrels are effective dispersers and partially eaten acorns are still viable, the vigour
of the seedlings may be less than seedlings grown from unpredated acorns. Grey squirrels
also predate birds' eggs and nestlings and may compete with other native acorn-eating
species. In England, short-term management to lesson the impact of grey squirrels on red
squirrels includes trapping of grey squirrels, reintroduction of red squirrels, use of
rodenticides such as warfarin in areas where there are no red squirrels and additional
feeding of red squirrels (by using "red-only" feeders) although the latter has not been
proven effective in Europe. Long-term management options include promoting red
squirrel habitat by maintaining continuous forest cover with an appropriate food supply.
More research is needed in the development of immuno-contraceptives to sterilize
squirrels by oral vaccination. Many of these control techniques may also be effective in
Garry oak ecosystems.
Chung, M. A. L., A. E. Hagerman and R. L. Kirkpatrick. 1997. Effects of tannins on
digestion and detoxification activity in gray squirrels (Sciurus carolinensis).
Physiological Zoology 70 (3) 270-277.
Authors' abstract: Acorn tannins may affect food preferences and foraging strategies of
squirrels through effects on acorn palatability and digestibility and squirrel physiology.
Captive eastern gray squirrels (Sciurus carolinensis) were fed 100% red oak (Quercus
and the higher glucuronidation activities observed in squirrels. Although the white oak
acorn diet had lower apparent protein digestibilities than the reference diet, it did not
suppress dry matter intake for a prolonged period or stimulate glucuronidation. Negative
physiological effects of a 100% red oak acorn diet suggest gray squirrels may require
other foods to dilute tannin intake and provide additional nutrients. To distinguish the
roles of different tannin types in the observed effects of acorn diets on squirrels, squirrels
were fed rat chow containing no tannins, 4% or 8% tannic acid (hydrolyzable tannin), or
3% or 6% quebracho (condensed tannin). Apparent protein digestibilities were reduced
by tannic acid and quebracho diets. Only the 8% tannic acid diet tended to increase
glucuronidation. Specific effects of tannins may largely depend on tannin type,
composition, and source and on other nutritional and physiological factors.
Craine, N. G., P. A. Nuttall, A. C. Marriott and S. E. Randolph. 1997. Role of grey
squirrels and pheasants in the transmission of Borrelia burgdorferi sensu lato, the Lyme
disease spirochaete, in the U.K. Folia-Parasitologica Ceske Budejovice 44 (2): 155-160.
Authors' abstract: In Britain, grey squirrels (Sciurus carolinensis Gmelin) and pheasants
(Phasianus colchicus Linnaeus) are important hosts of larvae and nymphs of Ixodes
L., the principal European vector of the Lyme disease spirochaete, Borrelia
burgdorferi sensu lato
. To test whether squirrels are competent hosts of B. burgdorferi s.
l., three females were trapped in the wild and then held in captivity. Following treatment,
each animal was exposed to uninfected xenodiagnostic I. ricinus ticks. Squirrel A (an
adult) which was inoculated experimentally with B. burgdorferi s.l., transmitted the
infection to xenodiagnostic ticks. In contrast, as C (an adult) became infected and
subsequently transmitted the infection experimentally to an uninfected hamster. The
results indicated that squirrel C had a disseminated infection acquired in the wild and
which persisted for at least 11 weeks. These data clearly demonstrate that grey squirrels
are amplifying and reservoir hosts of B. burgdorferi s.l. The strain associated with
squirrels was related to the B. afzelii genotype. Two observations implicated pheasants in
a similar role: (i) a high prevalence of infection in engorged larvae collected from trapped
pheasants, and (ii) the detection of B. burgdorferi s.l. (B. garinii genotype) in the wattle
of 1/10 pheasants using PCR. Xenodiagnostic experiments similar to those undertaken
with the squirrels are needed to confirm the role of pheasants in the transmission cycle of
Lyme disease spirochaetes.
Drake, J. C. and F. J. Brenner. 1995. Comparison of habitat preferences of gray and
fox squirrels in northwestern Pennsylvania. Journal of the Pennsylvania Academy of
Science 69 (2): 73-76.
Authors' abstract: Three woodlots in Crawford, Forest and Warren Counties in
Northwestern Pennsylvania were monitored for squirrel activity over a four month period
to determine if the black and gray morphs of the gray squirrel (Sciurus carolinensis) and
the fox squirrel (S. niger rufiventer) exhibit different habitat preferences. Based on 65
hours of observation, the two color morphs of the gray squirrel exhibited preferences,
with the black morph occurring more often in bottomland forests dominated by hemlock
(Tsuga canadensis) and American beech (Fagus grandifolia); whereas, the gray morph
and fox squirrels preferred the more open upland forests. The preference of the black
morph for the dense bottomland forest would provide a selective advantage against
predation while the reverse would be true for the gray morph and fox squirrels in the
more open upland habitats.
Eason, P. K. 1998. Predation of a female House Finch, Carpodacus mexicanus, by a
Gray Squirrel, Sciurus carolinensis. Canadian Field Naturalist 112 (4): 713-714.
Author's abstract: I observed a Gray Squirrel (Sciurus carolinensis) capture, kill, and
consume a fully flighted female House Finch (Carpodacus mexicanus). Gray Squirrels
rarely prey on vertebrates, and previous reports of their predation on birds record them
eating only birds' eggs and nestlings.
Ennis, T. 2002. Personal communication. The Nature Conservancy of Canada,
Victoria, BC.
Ennis is involved with restoration of the Cowichan Garry Oak Preserve. He states that
pellet rifles which meet the 200ft/s legal limit are very effective against both rabbits and
Faccio, S. D. 1996. Predation of an Eastern Chipmunk, Tamias striatus, by a Gray
Squirrel, Sciurus carolinensis. Canadian Field Naturalist 110 (3): 538.
Author's abstract: I observed a Gray Squirrel (Sciurus carolinensis), attack and kill an
Eastern Chipmunk (Tamias striatus) in Orange, Massachusetts. Published reports of Gray
Squirrel predation upon other vertebrates consist only of bird eggs and nestlings.
Fenske, C. T. J. and G. J. Niemi. 1997. Predation of artificial ground nests at two
types of edges in a forest-dominated landscape. Condor 99 (1): 14-24.
Author's abstract: Artificial ground nests were placed in medium-age or older forests
adjoining (a) stands of regenerating forest (vegetation lt 2 in high) where 'hard' edges
were created, and (b) stands of young forest (vegetation 2-8 m high) where 'soft' edges
were created. Nests were placed at three distances from the forest edge (0 in, 50 m, and
100 m). Two Northern Bobwhite Quail (Colinus virginianus) eggs were placed in each
nest and monitored after 7 and 14 days of exposure between late May and mid-July,
1994. Overall nest predation was 72% after 7 days and 85% after 14 days of exposure.
Predation near soft edges was significantly higher than near hard edges after both 7 and
14 days of exposure. Predation near the edges was significantly higher than away from
the edges after both 7 and 14 days of exposure. Two motion-sensitive cameras were used
to record the identity of predator species. Cameras documented 28 predation events
during 1,728 hours of operation, caused by eight species of mammals. The predators
included, in order of decreasing predation: fisher (Martes pennanti), Eastern chipmunk
(Tamias striatus), red-backed vote (Clethrionomys gapperi), red squirrel (Tamiasciurus
), deer mouse (Peromyscus maniculatus), black bear (Ursus americanus), gray
squirrel (Sciurus carolinensis), and striped skunk (Mephitis mephitis). The relationship
between edges, predator assemblages, and nest success is complex; more studies at the
landscape level are required to better understand the effects of these factors on avian
population dynamics.
Figala, J. and J. R. Tester. 1986. Comparison of seasonal rhythms of activity of gray
squirrels Sciurus carolinensis Rodentia in captivity and in the wild. Vestnik
Ceskoslovenske Spolecnosti Zoologicke 50 (1): 33-48.
Authors' abstract: Seasonal changes in the activity rhythm in captive grey squirrels
(Sciurus carolinensis) were recorded by a photocell system at the Cedar Creek Natural
History Area, Minnesota [USA]. Photocell recordings from grey squirrels near the Arctic
Circle at Kuusamo, Finland and at Andechs, West Germany were analyzed and compared
with those from Cedar Creek. Activity rhythms of wild squirrels, and also of the captives,
were monitored by radio telemetry at Cedar Creek. The duration of activity time (.alpha.)
in both captive and wild squirrels did not follow the duration of the photoperiod
throughout the year. The very short .alpha. in late winter might be under the control of
exogenous factors other than light, especially in wild squirrels. The marked increase in
length of activity in September in wild squirrels was probably related to mast harvesting
behavior. Seasonal differences in phase angle and duration of activity indicate larger
variations in wild than in captive squirrels. Secondly, our data on grey squirrels suggest
that day-active mammals exhibit larger variations in phase angle differences and duration
of activity than day-active birds.
Fischer, R. A. and N. R. Holler. 1991. Habitat use and relative abundance of gray
squirrels in southern Alabama, USA. Journal of Wildlife Management 55 (1): 52-58.
Authors' abstract: We studied habitat use and estimated relative abundance of gray
squirrels (Sciurus carolinensis) in 3 habitats at the Solon Dixon Forestry Education
Center, Covington and Escambia counties in southern Alabama, from January 1987 to
September 1988. Three representative stands of even-aged pine, mixed pine-hardwood,
and hardwood were selected for study, and a 50-station trapping grid was established in
each. We captured 603 squirrels 1,586 times. Relative abundance was based on the
minimum number of squirrels known alive. Squirrel abundance in hardwood and in
mixed pine-hardwood habitat did not differ (P = 0.47), but abundance in even-aged pine
was lower (P < 0.001) than that in either of the other 2 habitats. We measured 6 habitat
variables in each study area. Moderately open understories with a dense shrub crown
(vegetation between 1 and 5 m) component appear to be important to squirrel abundance.
To determine habitat preference, we fitted 17 gray squirrels with radio transmitters.
Narrow bands of hardwoods along ephemeral streams (i.e., hardwood stringer) were an
important component of gray squirrel habitat in even-aged pine and mixed pine-
hardwood stands. Forest management should include the retention of hardwood stringers
within pine and mixed pine-hardwood stands.

Fisher, J. T. and G. Merriam.
2000. Resource patch array use by two squirrel species
in an agricultural landscape. Landscape Ecology 15 (4): 333-338.
Authors' abstract: Eastern grey squirrels (Sciurus carolinensis) and North American red
squirrels (Tamiasciurus hudsonicus) were studied among wooded patches within an
agricultural mosaic. Fifteen sites south of Ottawa, Canada, with differing landscape and
local features were censused using tracking boards placed in a woods or wooded
fencerow. Regression analyses of landscape compositional and physiognomic variables
within a 1-km radius isolated the best predictors of grey and red squirrel abundance and
activity. Grey squirrels were found in both small woods and fencerows in farm
landscapes but were not found in large woods. A polynomial regression of wooded patch
size explained 79% of the variance in grey squirrel abundance. Grey squirrel activity was
correlated with the percent cover of soybeans in the landscape. Red squirrels were found
in fencerows, small and large woods; activity was correlated with the percent cover of
both woods and corn crop in the surrounding landscape. These results indicate that
distributions of both species are influenced by multiple landscape elements, but that grey
squirrels may rely on fragmented agricultural landscapes whereas red squirrels make
more use of both native woodland and altered landscapes.
Fitzgibbon, C. D. 1993. The distribution of grey squirrel dreys in farm woodlands: The
influence of wood area, isolation and management. Journal of Applied Ecology 30 (4):
Author's abstract: 1. Sixty-eight deciduous woodlands, ranging in size from 0.2 to 12.5
ha, were surveyed in East Anglia, UK, and the density of grey squirrels Sciurus
estimated from drey counts. 2. Squirrel dreys were more likely to occur in
woods that (i) were larger, (ii) were closer to another wood of at least 5 ha in size, (iii)
contained oak Quercus spp., beech Fagus sylvatica or hazel Corylus avellana, and (iv)
were surrounded by a greater density of hedgerows. 3. The overall density of woodland in
the vicinity, the distance to a wood of at least 0.5 ha in size, and the presence/absence of
five other tree species did not influence squirrel drey distribution between the woods. 4.
In woods that contained squirrel dreys density was higher in woods with a greater density
of large trees (diameter in excess of 50 cm) and in woods which were closer to another
wood of at least 0.5 ha in size. 5. Since reducing the probability of squirrels inhabiting a
plantation will reduce the risk of young trees being bark-stripped, the results of this study
have implications for the design of new farm woodlands.
Fox, J. F. 1982. Adaptation of gray squirrel behaviour to autumn germination by white
oak acorns. Evolution. 36(4): 800-809.
Author’s summary: Acorns of some species of white oaks are nondormant, germinating
in autumn soon after falling to the ground. When burying acorns of at least three such
white oak species, gray squirrels often kill the growing point of the seed. This prevents
the loss (to the squirrel) of up to 50% of the food material, which would otherwise be
transferred into the seedling before the squirrel recovered the seed in winter. Nondormant
acorns that are buried undamaged produce a seedling taproot engorged with food
reserves; because of this, if a squirrel subsequently removes the acorn in winter, the
seedling is still capable of growth the following spring. Squirrels do not kill the growing
point of acorns of red oaks, which are dormant-seeded, before caching them. The
squirrels’ behavior is interpreted as a countertactic evolved to deal with autumn-
germinating acorns. Autumn germination may be a tactic evolved as an ‘escape’ from
post-dispersal predation by squirrels. Escape is not completely eliminated by the
squirrels’ countertactic; because of exceptions to the behavior, especially among juvenile
squirrels, some 48% of white oak acorns are cached unharmed and capable of ‘escape’.
Genovesi, P. 2000. Box 3: Eradication of the grey squirrel in Italy: failure of the
programme and future scenarios. In: Convention on the conservation of European
wildlife and natural habitats standing committee: Guidelines for eradication of terrestrial
vertebrates - a European contribution to the invasive alien species issue. Website:

At the time of publication, Italy was the only continental location in Europe where
eastern grey squirrels were found in the wild. Genovesi outlines the impact of eastern
grey squirrels including stripping bark from trees, competing with European red squirrels,
and acting as a vector of parapoxvirus. After the introduction of grey squirrels, there was
a lag time before the population spread. In order to prevent the spread to other countries
and other regions within Italy, the Italian government recommended the eradication of
grey squirrels from the country. A plan for experimental removal of grey squirrels was
developed using live traps and humane euthanasia with halothane anaesthesia
administered under veterinary supervision. Demonstrations by animal rights activists and
subsequent legal action by the activists brought the project to a standstill. In the absence
of any control, the range of the grey squirrel continues to expand. This project provides
valuable lessons on the need for public education and involvement with any form of
small mammal control in Garry oak ecosystems.
Gonzales, E K. 1999. Eastern grey squirrels in British Columbia: an introduction to an
introduction. Discovery 28: 22-25.
Author's abstract: The eastern grey squirrel (Sciurus carolinensis) was introduced to
British Columbia sometime prior to 1914. The population remained isolated in Stanley
Park until sometime in the 1970's, when viable populations were reported in several
municipalities. Naturally adept at adaptation and dispersal, the squirrels have since
expanded their density and distribution throughout Greater Vancouver. A human
commensal species, they have probably had anthropogenic aid in their dispersal to other
cities on mainland British Columbia and Vancouver Island.
Gonzales, E. K. 2000. Distinguishing between modes of dispersal by introduced eastern
grey squirrels (Sciurus carolinensis). M.Sc. Thesis, University of Guelph, Guelph, ON.
Although the spread of grey squirrels in Europe has been well documented, the
mechanism for dispersal has not been carefully analyzed. The stochastic spread of the
species in Europe has been associated with variations in the habitat but no models have
been created to describe the spread. Gonzales used records of grey squirrels populations
in British Columbia to determine whether humans have assisted the dispersal of this
species. Grey squirrels were introduced to Vancouver in 1909 and Victoria in 1966.
There was a time lag before the populations spread due in part to small population
effects. Gonzales analyzed the dispersal of both populations by using weighted surface
analysis. This approach takes into account habitat preferences, rate of spread and
landscape barriers to dispersal. She concludes that humans have translocated grey
squirrels and helped spread this species.
Gonzales, E.K. 2002. Personal communication. Ph.D. student, Centre for Applied
Conservation Research, University of British Columbia, Vancouver, BC. Nove mber 14,
Gonzales has researched the habitat preferences and spread of eastern grey squirrels
(Sciurus carolinensis) in Victoria and Vancouver, British Columbia. She concludes that
the spread of the squirrels is facilitated by direct translocation by people and by
increasing urbanisation that creates their preferred habitat. Grey squirrels do not survive
well in coniferous forest and the denser forest seems to slow their spread. Gonzales notes
that because grey squirrels do better in modified environments with horticultural species
than they do in natural British Columbian environments and Garry oak ecosystems are
highly urbanized, it is difficult to determine the effect on Garry oak ecosystems.
Gonzales has not found any conclusive literature that confirms that eastern grey squirrels
damage acorns of Garry oaks. Instead, the literature she has read indicates the squirrels
are effective dispersers, that white oaks (including Garry oak) are not a preferred food
source and that even partially eaten acorns are still viable. Both introduced grey squirrels
and the native red squirrels eat bulbs and may be a predator on camas in Garry oak
ecosystems. Both native and grey squirrels eat birds eggs and nestlings. However,
because grey squirrels are in urban areas, cats may be a more serious predator. Gonzales
has also found no evidence (other than anecdotal) that grey squirrels displace native red
squirrels. She has observed both squirrels coexisting in areas where the grey squirrels
have been introduced (e.g. Stanley Park) and the two species prefer different habitat (red
squirrels prefer conifer forest, grey squirrels prefer residential areas) although the
squirrels may interact at marginal habitats (e.g., Beaver Lake Park, Victoria, British
Columbia). During one on one interactions, red squirrels are typically dominant because
of their territorial nature but it is possible that grey squirrels could reach higher densities
and "swamp" the red squirrels. Although red squirrels were previously more widespread
in Victoria, Gonzales thinks the decrease is probably due to loss of habitat. Other authors
have used the decline of European red squirrels (Sciurus vulgaris) after the introduction
of eastern greys to infer an impact on our native red squirrels in British Columbia.
However, Gonzales notes European red squirrels are very different from our red squirrels
and European reds have not been displaced in conifer habitats (e. g., in Scotland).
Management opinions: Eradication of grey squirrels is very expensive and may be
impossible once the species is established because they are efficient dispersers and will
quickly reinvade an area. In Britain during the 1950’s, millions of dollars were spent to
try to eradicate grey squirrels with no real results. The best chance to eradicate grey
squirrels is before they establish. However, Gonzales believes that the grey squirrel is
already established in most of the Capital Regional District. Gonzales says that before
management of grey squirrels is attempted, it is important to determine whether or not
they impact Garry Oak ecosystems and whether the increased spread of grey squirrels is
due to habitat alteration. In order to prevent further spread of grey squirrels, people
should be educated to not translocate grey squirrels and to not to feed them either directly
or indirectly. It will be very challenging to avoid feeding grey squirrels because they are
attracted to tulip bulbs, open compost, garbage, nut trees, fruit trees, and bird feeders.
Gorman, O. T. and R. R. Roth. 1989. Consequences of a temporally and spatially
variable food supply for an unexploited gray squirrel Sciurus carolinensis population.
American Midland Naturalist 121 (1): 41-60.
Authors' abstract: The demography and spatial distribution of a gray squirrel (Sciurus
) population was studied with respect to differences in habitat quality and
food production in a heterogeneous Delaware woodlot from 1972-1973. In 1971 a large
mast crop was produced, followed by a poor 1972 crop and a partial recovery in 1973.
The squirrel population declined from 116 individuals in summer 1972 to 82 in fall 1973.
Major components of the decline were losses of 1972 juveniles and 2-5-year-old females,
and curtailed breeding in 1973. Squirrels were segregated among five study plots that
represented areas of differing habitat quality and food production within the woodlot. The
distribution of the sexes among the plots was significantly heterogeneous in summer and
fall 1972 and summer 1973 (P < 0.10, G-test); plots with poorer mast production had a
preponderance of females (.hivin.x percent of individuals = 62%) while males
predominated in plots with the best mast resources (.hivin.x = 64%). In particular, adult
males and yearlings (both sexes) were skewed towards high- mast plots while adult
females were more abundant in low- mast plots. Juveniles showed no discernable pattern
of distribution among plots. Losses were greater than expected from low-mast plots and
less than expected from high- mast plots, especially for juveniles, yearlings, and females.
The pattern of spatial variation of food abundance, sex (and possibly age) ratios and
disappearance rates suggests a model of population regulation in which subordinates are
relegated to suboptimal sites and bear major stress and losses when population density is
high and food resources dwindle.
Gurnell, J. 1996. The effects of food availability and winter weather on the dynamics
of a grey squirrel population in southern England. Journal of Applied Ecology 33 (2): 325-338. Author's abstract: 1. The population ecology of grey squirrels Sciurus carolinensis living in a 9-ha oak Quercus robur wood in southern England was studied between 1976 and 1987 using live-trapping techniques. Trapping was carried out in winter, spring and summer. The availability of tree seeds during the autumn of each year, and the severity of cold weather over each winter were also measured to examine their effects on squirrel population dynamics. 2. Capture probabilities of squirrels in winter, and to a lesser extent in spring, were inversely related to food availability and data from these two seasons were not considered dependable. The analyses concentrated on the summer populations. 3. The long-term average summer density of squirrels was high at 8.8 ha-1 (SE 3.41 ha-1) demonstrating that the oak wood was high quality habitat for grey squirrels. Over 10 of the 12 years, summer densities were remarkably similar, ranging between 7 ha-1 and 10 ha-1 (mean 8.5 ha-1, SE 0.95 ha-1).However, numbers were driven upwards in 1977 to a density approaching 18 ha-1 and downwards in 1982 to a density of about 3 ha-1: a 6-fold difference. 4. In good seed years, breeding starts in December, in poor seed years the start of breeding is deferred until the spring. There was no or very little spring breeding in 5 years when food supplies were poor. Female reproductive success was positively associated with food availability. Partial correlation analysis showed that the level of association was not improved when the effects of winter weather were taken into account. The number of new adult females in the summer population was positively associated with food availability but there was no association between new males and food. This suggests that food availability is more important to breeding females than breeding males. 5. Persistence from summer to winter was positively associated with food availability, but persistence from summer to spring and to the following summer were not. Partial correlation analyses showed that the severity of winter weather tended to mask the effects of food availability on persistence and the partial correlation coefficients were higher when the effects of weather were held constant. Adult females had the highest persistence between summers (52%, n = 11, SE 6%), followed by juvenile females (38%, n = 7, SE 8%), adult males (36%, n = 11, SE 4%), and juvenile males (21%, n = 7, SE 7%). The persistence of adult males but not females was inversely related to the initial number of males present. 6. In males, there was no significant difference in winter body mass between years and winter body mass was not associated with food availability, although there were very few data for winters when the food supply was good. In 7 years when the food supply was poor to moderate, there was an increase in mean body mass between summer and winter in 4 years, and a decrease in 3 years. 7. The data were explored using ordination techniques; first a standardized principal component analysis and then the canonical form of principal component analysis or redundancy analysis. The analysis was carried out on years derived from MNA of males and females and various combinations of the environmental variables: food availability (FOOD) and the severity of winter weather (TEMP). The ordination biplots clearly showed the high correlation between MNA males and MNA females and that FOOD was the most important environmental variable. TEMP on its own had no effect but FOOD times TEMP was important. 8. Following on the exploratory data analysis and for predictive purposes, a general linear model between the numbers of squirrels in the summer populations and sex, FOOD and FOOD times TEMP as
explanatory variables accounted for 77% the variance in squirrel numbers among years.
9. This study shows that tree seed availability is the most important factor limiting grey
squirrel densities, but this factor both positively and negatively interacts with the severity
of winter weather to affect grey squirrel population dynamics.
Gurnell, J., L. A. Wauters, D. Preatoni and G. Tosi. 2001. Spacing behaviour,
kinship, and population dynamics of grey squirrels in a newly colonized broadleaf
woodland in Italy. Canadian Journal of Zoology 79 (9): 1533-1543.
Author's abstract: Eastern grey squirrels, Sciurus carolinensis, introduced to Britain and
northern Italy are replacing the native Eurasian red squirrel, Sciurus vulgaris. We studied
the pattern of colonization of a high-quality broadleaf woodland by grey squirrels by
means of livetrapping and radio-tracking. The studies started in July 1996, when six grey
squirrels (four males, two females) first colonized the woodland, and lasted until
November 1998, when densities exceeded those of the local red squirrel population. Grey
squirrel colonization was rapid, with a high proportion of adult and yearling females
breeding. Juvenile recruitment was also higher than in stable populations in Britain. Adult
survival was better in 1997 (83%) than in 1998 (47%), with predation accounting for
67% of losses in 1998. This indicates the effects of local predator communities on the
colonization process. Densities of grey squirrels were moderate in 1998, with a maximum
of 1.9 squirrels/ha and we expect density to increase further. Adult home range sizes were
three to four times larger than those of subadults, and male ranges were larger than those
of females. Body mass was positively correlated with both total home range size and
core-area size. Core-area size for adults was inversely correlated with food availability.
Juvenile female grey squirrels were philopatric, forming female kin groups, while most
juvenile males settled outside the mother's home range.
Hadj, C. L. Z., M. A. Steele and P. D. Smallwood. 1996. Caching decisions by grey
squirrels: A test of the handling time and perishability hypotheses. Animal Behaviour 52
(5): 941-948.
Author's abstract: This study was designed to investigate the relative effects of seed
perishability and handling time on the caching preferences of grey squirrels, Sciurus
, and to test the predictions for caching behaviour that follow from these two
hypotheses. Free-ranging squirrels were presented with acorns from two oak subgenera,
Erythrobalanus and Leucobalanus, that vary in perishability (due to germination
schedules) and handling time (due to acorn size). In six separate caching experiments,
individual squirrels were sequentially presented with two acorn types, so that each paired
treatment varied in handling time and/or perishability. Caching responses were recorded
for each acorn, along with eating and caching times. Squirrels consistently consumed
acorns of high perishability and cached acorns of low perishability, without regard to
handling time. This result suggests that the perishability of seeds exerts a greater
influence than handling time on the grey squirrel's decision to cache acorns.
Huggins, J. G. and K. L. Gee. 1995. Efficiency and selectivity of cage trap sets for
gray and fox squirrels. Wildlife Society Bulletin 23 (2): 204-207.
Author's abstract: We studied 4 cage trap sets for gray squirrels (Sciurus carolinensis)
and fox squirrels (S. niger) in the Cross Timbers region of southcentral Oklahoma.
During 4,308 trap-days in October-December 1991, traps set on platforms caught the
highest percent of gray and fox squirrels, but large variation among trap sites prevented
statistical differentiation of trap sets. Orientation of traps at sets did not influence
mechanical performance of traps. Although more involved to construct, platform-
mounted traps were more convenient to monitor than traps mounted on the trunk, a limb,
or the ground.

Ivan, J. S. and R. K. Swihart.
2000. Selection of mast by granivorous rodents of the
central hardwood forest region. Journal of Mammalogy 81 (2): 549-562.
Authors' abstract: We used cafeteria-style feeding trials with 8 types of mast in various
combinations to examine differences in resource selection among 5 syntopic species of
granivorous forest rodents in west-central Indiana. Patterns of resource selection
corresponded to differences in phylogeny and body size of granivores, with greatest
similarities among closely related species of similar body size. Breadth of resource use
varied inversely with body size in our trials. Resource selection by Sciurus carolinensis,
S. niger
, and Tamiasciurus hudsonicus was correlated positively with caloric and lipid
content of mast and its size, whereas selection by Glaucomys volans was correlated
negatively with the percentage of protective tissue associated with seeds. Laboratory
trials indicated that T. hudsonicus and G. volans discriminate among mast of comparable
physical and chemical composition on the basis of size, with a preference for larger
seeds. Contrary to our expectations, T. hudsonicus, a recent immigrant from the boreal
forest, did not exhibit a preference for seeds of red pine (Pinus resinosa) relative to mast
of hardwood species. G. volans and Peromyscus leucopus tended to consume perishable
white oak acorns immediately and to cache a substantial portion of less perishable seeds
of nonpreferred species. Our results demonstrate the potential for considerable overlap in
resource use among members of this guild. Guild members also seem to be affected
differentially by physical and chemical properties of mast, and patterns of resource
selection reflect contrasting foraging constraints under which these animals operate.
Jacobs, L. F. and E. R. Liman. 1991. Gray squirrels remember the locations of buried
nuts. Animal- Behaviour 41 (1): 103-110.
Authors' abstract: It has previously been assumed that grey squirrels, Sciurus
, cannot remember the locations of nuts they buried, and hence must relocate
nuts by their odour. This assumption was tested by measuring the accuracy of cache
retrieval of captive squirrels. Each squirrel was released alone into an outdoor arena,
where it cached 10 hazelnuts. After a delay of 2, 4 or 12 days, each squirrel was returned
to the arena and tested for its ability to retrieve nuts from its own cache sites and from 10
cache sites used by other squirrels. Although each squirrel's own caches were close to the
caches of other squirrels, the squirrels retrieved significantly more nuts from their own
sites than from sites used by other squirrels, after all delays. The retrieval accuracy of the
squirrels under these conditions indicates that while grey squirrels can locate buried nuts
by their odour, they can also remember the individual locations of nuts they have buried.
Kenward, R. E. and K. H. Hodder. 1998. Red squirrels (Sciurus vulgaris) released in
conifer woodland: The effects of source habitat, predation and interactions with grey
squirrels (Sciurus carolinensis). Journal of Zoology 244 (1): 23-32.
Authors' abstract: Fourteen radio-tagged red squirrels were released in pine woodland
containing grey squirrels. Movements of the squirrels were related to the tree species of
the donor site. Survival after release was lower than for the grey squirrels: of 11 red
squirrels that survived at least a week, only three survived more than three months and
none for four months. More than half were eaten or cached by predators, mainly foxes; an
experiment with grey squirrel carcasses indicated that they had been killed, not
scavenged after death. Hypertrophied adrenals, disease and loss of weight indicated stress
as another factor in the deaths. Data on overlap of core ranges, and reluctance of red
squirrels to enter traps used by grey squirrels in the mixed population, indicated
interference competition between the two species, with grey squirrels possibly dominant.
We recommend: (i) that care should be taken to release translocated animals in similar
habitat to their origin; (ii) that grey squirrels should be excluded from future release areas
until red squirrels have settled and, before biodiversity is reduced by landscape
management for red squirrels; (iii) more research to determine whether interactions with
grey squirrels or differential predation will ultimately displace red squirrels in conifers.
Kenward, R. E., K. H. Hodder, R. J. Rose, C. A. Walls, T. Parish, J. L. Holm, P. A.
Morris, S. S. Walls and F. I. Doyle.
1998. Comparative demography of red squirrels
(Sciurus vulgaris) and grey squirrels (Sciurus carolinensis) in deciduous and conifer
woodland. Journal of Zoology 244 (1): 7-21.
Authors' abstract: The demography of red and grey squirrels was studied by live-trapping
and radio-tagging at 14 deciduous and conifer sites in southern Britain and at eight
conifer sites for one year in northern England. Densities and productivity correlated with
tree seed crops for both squirrel species in deciduous and conifer habitats. Productivity
was reduced by high density of full- grown squirrels relative to seed abundance. In oak-
hazel woods, demography of grey squirrels correlated with abundance of acorns but not
of hazel-nuts, whereas density and productivity of red squirrels correlated with hazel- nut
abundance. Correlations of female density and productivity with pine-cone crops did not
differ between red and grey squirrels. Predators ate many radio-tagged grey squirrels in
conifers, and annual survival was only 50% compared with 80-82% for both species in
other habitats. Grey squirrel populations in southern conifer sites were sustained by
immigration, and at northern sites female density correlated with oak abundance within
500 m. Failure to exploit acorn crops puts red squirrels at a competitive disadvantage in
deciduous woodland. Red squirrels had higher survival than grey squirrels in conifers,
which may give them an advantage in that habitat, but could also have been explained by
a lack of predators on their island study site.
Koprowski, J. L. 1991. Response of fox squirrels and gray squirrels to a late spring
early summer food shortage. Journal of Mammalogy 72 (2): 367-372.
Author's abstract: The response of adult and juvenile fox squirrels (Sciurus niger) and
gray squirrels (S. carolinensis) to a shortage in their two major May-June foods was
monitored and compared to a year of typical food abundance. Squirrels foraged more
frequently, but less efficiently, during the year of fruit failure than during the typical year.
Juvenile survival of both species was reduced during the year of fruit failure, but adult
survival remained high. Juvenile losses occurred during late June when weights of adults
and juveniles were lower than in the year of typical fruit abundance. By influencing
juvenile survival and body condition of adults, late spring-early summer can be a critical
period for populations of tree squirrels.
Lawniczak, M. K. 2000. Sciurus carolinesis: Eastern Grey Squirrel. Website
maintained by University of Michigan. Website:
November 19, 2002.
Lawniczak describes the geographic range of the eastern grey squirrel and gives a
complete description of the species including body measurements and dental formulas.
The diet of grey squirrels is listed as nuts, flowers and buds of hardwood trees
supplemented by fruit, seeds, bulbs and flowers of a range of plants, agricultural crops,
insects and rarely frogs and birds' eggs and nestlings. Reproductive biology is thoroughly
described from mating through weaning. There are two breeding periods and gestation is
reported as 44 days. Females usually mate at 1.25 years, will mate with several males and
can breed for 8 years producing litters of 2-4 young. Grey squirrels are most active before
sunrise and before sunset and have varying home ranges depending on the season and
population density. Squirrels nest in cavities and dreys in the crotch of trees. Grey
squirrels are reported to prefer continuous forests of greater than 40 hectares that produce
foods that can be cached for winter. The website uses only three mammal guides as
references and does not refer to any peer reviewed papers.
Linzey, D. and C. Brecht. 2002. Eastern Gray Squirrel. Website maintained by
Wytheville Community College, Wytheville, Virginia. Website:
Accessed: November 19, 2002.
The website gives a complete species description of the eastern grey squirrel (including
body measurements and skull diagrams), phylogeny, and native distribution in North
America. In Great Smoky Mountains National Park, Colorado, grey squirrels are native
and are most common in oak and beech woodlands and mixed conifer forests. The site
also provides reproductive information from the park. There are two mating seasons
(September to February and June to July) and young are born 40 days later. The 1-6
young are raised by the mother and are weaned at 8-9 weeks. Grey squirrels can live 20
years in captivity and up to 10 years in the wild. Grey squirrels are most active in early
morning and late afternoon and are primarily arboreal. Grey squirrels eat the flowers,
fruit, twigs and buds of deciduous shrubs and trees as well as mushrooms and insects.
Grey squirrels have been killed by rattlesnakes, bobcats and automobiles in Great Smoky
Mountains National Park.
Lurz, P. W. W., P. J. Garson and S. P. Rushton. 1995. The ecology of squirrels in
spruce dominated plantations: Implications for forest management. Forest Ecology and
Management 79 (1-2): 79-90.
Authors' abstract: Red Sciurus vulgaris and grey Sciurus carolinensis squirrel ecology in
conifer forests in Europe is reviewed with reference to squirrels in similar habitats in
North America. Red squirrels appear to perform best in conifer forests that contain a
large proportion of pine Pinus spp., with or without Norway spruce Picea abies. Grey
squirrels, in contrast, perform best in conifer plantations that have oak Quercus spp. and
acorns available nearby. A generalized linear model to predict red squirrel density based
on forest size, composition and the presence or absence of a Norway spruce cone crop is
explained and forest management recommendations for a red squirrel conservation area
in Kielder Forest are made.
Lurz, P. W. W., S. P. Rushton, L. A. Wauters, S. Bertolino, I. Currado, P. Mazzoglio
and M. D. F. Shirley.
2001. Predicting grey squirrel expansion in North Italy: A
spatia lly explicit modelling approach. Landscape Ecology 16 (5): 407-420.
Authors' abstract: There is growing concern about the spread of the North American grey
squirrel (Sciurus carolinensis) in northern Italy which were introduced into Piedmont in
1948. They have since spread across the Po-plain covering an area of approximately 450
km2 and continue to expand their range. In parallel to what has been observed in Britain
and Ireland, grey squirrels replace the native red squirrel (S. vulgaris) and damage poplar
(Populus) plantations through bark-stripping. Spatially explicit population dynamics
models have been successfully used to predict the spread of grey squirrels in East Anglia,
England. We extended a previous approach employing a sensitivity analysis where life
history and other demographic inputs are generated using Latin Hypercube Sampling
from the known ranges of each input parameter, and applied it to Italy using field data
collected in Piedmont. The analysis indicated that reproductive output was the most
important factor determining total population size present in Piedmont. The structure and
composition of woodland habitats around the introduction site suggested that initial grey
squirrel expansion would have been slow and subject to emigration rates from the
available habitat blocks. A comparison of the 1996 survey results with model predictions
indicated that a mean litter size of three young gave the best fit with the observed
distribution and we use this to predict future grey squirrel spread. We also present a
'worst case' scenario in which grey squirrels experience improved reproductive success
due to the availability of high quality habitats beyond the Po plain. In both cases they
could disperse along existing continuous woodland corridors into France between 2039-
2048. The case of the grey squirrel highlights the problems of implementing conservation
conventions and the resulting conflicts between wildlife management, public perception
and local political support and the narrow time frame that is available to control alien
species effectively before it is too late. If allowed to spread, grey squirrels have the
potential of becoming a European forest pest species and are likely to replace the native
red squirrel in large parts of its range.
MacDonald, A. 2002. Personal communication. Birder, Victoria, BC.
MacDonald has observed native raptors feeding on eastern grey squirrels. Maintaining
habitat for hawks and owls, installing raptor perches and maintaining standing, dead
trees, also known as wildlife trees, will also encourage the presence of birds of prey and
help control squirrel populations. The introduction of small mammals to Garry oak
ecosystems may have caused increases in populations of some native raptors and aided
the range extensio n of barred owls into these areas.
McCarthy, B. C. 1994. Experimental studies of hickory recruitment in a wooded
hedgerow and forest. Bulletin of the Torrey Botanical Club 121 (3): 240-250.
Author's abstract: An examination of the vegetation in and around an old-growth oak-
hickory forest in Central New Jersey suggested that hickories (Carya spp., Juglandaceae)
were not regenerating in the forest at the same rate as in adjacent wooded hedgerows (5-7
m wide corridors dominated by trees and shrubs). The goal of this study was to
experimentally examine how factors affecting seed and seedling survival might account
for these differential recruitment patterns in contrasting landscape elements. To
determine seed discovery efficiency by small vertebrates, I planted seeds of mockernut
hickory (C. tomentosa (Poir.) Nutt.) with and without their aromatic husk in both forest
and hedgerow. Regardless of diaspore type or habitat, seed discovery by herbivores was
found to be 85-100% after only 5 days. Gray squirrels (Sciurus carolinensis), the
principal predator-disperser, were determined to be equally abundant in both landscape
elements. To assess the effects of diffuse competition and predation on seedling
establishment and survival, I constructed split-plot shade/exclosure cages into which 576
seedlings were explanted and subsequently monitored (survival and mortality agent) for
three years. Browsing by deer and rabbits resulted in considerable mortality after one
year, particularly in the forest (64% mortality) compared to the hedgerow (21%
mortality). During the second year, the major source of mortality switched to
physiological stress resulting from drought. Mortality due to drought stress was more
noticeable in the hedgerow. By the end of the third year few seedlings remained alive (ca.
196 in forest, 10% in hedgerow). Over the 3-yr period, a small percentage of seedlings
were lost due to other factors such as root grubbing, whole plant removal, and litterfall.
Shading (50%), to emulate diffuse competition by overstory, was not found to affect
survival to any significant extent in either habitat. Phytophagous insects did not result in
any observable mortality but did remove 1-10% of the leaf area of the majority of
seedlings in both habitats in each field season. I conclude that certain stages of
recruitment may be significantly influenced by the presiding landscape element.
McShea, W. J. 2000. The influence of acorn crops on annual variation in rodent and
bird populations. Ecology 81 (1): 228-238.
Author's abstract: I recorded mast production by oaks (Quercus sp.) at 12 forested sites
in western Virginia for 6-12 yr and measured its impact on the abundance of small
mammals, understory vegetation, and artificial- nest predation. White-tailed deer
(Odocoileus virginianus) were excluded from half the 4-ha sites after at least one season
of data collection. My hypothesis was that annual variation in acorn crops affected
multiple species and that the strength of those interactions is mediated by white-tailed
deer. The acorn crop was variable across sites and year, with some of the between-site
variability explained by differences in elevation. All sites experienced at least one mast
failure, and mast failure years were generally consistent across sites. White- footed mouse
(Peromyscus leucopus), eastern chipmunk (Tamias striatus), and gray squirrel (Sciurus
) populations were significantly correlated with annual fluctuations in the
acorn crop. The exclusion of deer had a significant impact on P. leucopus and T. striatus
populations by increasing the number of animals captured following low acorn mast
years. Annual fluctuations in the acorn crop, but not in rodent densities, were
significantly correlated with the rates of predation on artificial nests the next summer.
There was no significant interaction between predation rates and the exclusion of deer.
An index from the Breeding Bird Survey (BBS) for Virginia was used to measure
regional numbers for 11 common species captured at the sites. The index for two
understory species was significantly negatively correlated with the mean acorn crop
measured 2 yr previously. The effect of white-tailed deer on the forest community was
not consistent across all conditions, as sites with large acorn crops were not strongly
influenced by deer. These data are consistent with the hypothesis that mast crops from
oaks serve as important determinants of community function within Appalachian forests.
McShea, W J. and G. Schwede . 1993. Variable acorn crops: Responses of white-tailed
deer and other mast consumers. Journal of Mammalogy 74 (4): 999-1006.
Authors' abstract: We examined movements and behavior of female white-tailed deer
(Odocoileus virginianus) relative to the acorn mast- fall from 1986 through 1989 in a
mature deciduous forest in Front Royal, Virginia. Ten white-tailed deer with
radiotransmitters increased their home range to incorporate acorn-producing areas during
mast- fall. Consumption of acorns by deer constituted ca. 50% of foraging time during
peak mast- fall; average consumption rate was 0.75 acorns/min searching. Although the
number of acorns eaten by deer was correlated with mast- fall, a prolonged time was spent
searching for acorns after mast- fall. Deer consumed 70% of marked acorns placed out
during mast- fall, while medium-sized animals (e.g., Tamias striatus, Sciurus niger,
Sciurus carolinensis
) consumed 61% of acorns placed out later in autumn. We
hypothesize that high densities of deer may limit populations of more mast-dependent
species, particularly at low acorn-crop densities.

Moore, H. D. M., N. M. Jenkins and C. Wong.
1997. Immunocontraception in
rodents: A review of the development of a sperm-based immunocontraceptive vaccine for
the grey squirrel (Sciurus carolinensis). Reproduction Fertility and Development 9 (1):
Authors' abstract: The strategy for developing contraceptive vaccines for wild rodents
will depend on the species. In rats and mice, high all- year birth rates, high levels of
dispersal and promiscuous mating systems suggest that, if immunocontraception was
used alone, gt 90% of the population would have to sterilized to achieve the desired
control. In Britain, the grey squirrel (Sciurus carolinensis) may be a better candidate to
investigate the feasibility of a contraceptive vaccine in rodents. This introduced species is
a seasonal breeder with a much lower population turnover than rats or mice. As well as
causing damage to woodland, it has ousted the native red squirrel (S. vulgaris) from most
of the UK. A humane and selective method for the control of grey squirrels is therefore
highly desirable. Numerous sperm-specific antigens have been identified on rodent
spermatozoa. Monoclonal antibodies to particular components block sperm-egg
interactions in laboratory animals and cross-react with grey squirrel spermatozoa. In vitro
fertilization assays indicate that squirrel sperm-egg binding may be inhibited also.
Currently, a cDNA library obtained from grey squirrel testis is being screened to identify
genes encoding specific sperm antigens involved in fertilization. Methods of enhancing
immunogenicity after oral immunization using microparticle carriers and immune-
stimulating complexes are currently under investigation.
Mountford, E. P. 1997. A decade of grey squirrel bark-stripping damage to beech in
Lady Park Wood, UK. Forestry 70 (1): 17-29.
Author's abstract: The scale and distribution of American grey squirrel (Sciurus
) bark-stripping damage to beech (Fagus sylvatica) stems was monitored in a
mixed broadleaved woodland retained as a Research Natural Area through the use of
permanent transects. During an initial outbreak of debarking damage in 1993 almost one-
third of beech individuals gtoreq 4 cm d.b.h. in stands of 40 years' growth were badly
damaged and by 1993 this level of damage had risen dramatically to over 50 per cent.
One-third of badly damaged individuals in 1983, including a number of potential canopy
dominants, died during the decade, but some that survived grew very vigorously.
Throughout squirrels preferentially debarked intermediate sized (10-25 cm d.b.h.) stems
in particular parts of the stands aged 40-50 years, apparently tending to select stems that
were growing rapidly. Other species and stand areas of gt 100 years' growth remained
largely unscathed. Within the 10- year period squirrels had critically affected the
successional development of the wood.
Nagorsen, D. W. 2002. An identification manual to the small mammals of British
Columbia. Ministry of Sustainable Resource Management, Ministry of Water, Land and
Air Protection, Royal British Columbia Museum, Victoria, BC.
The field guide is designed for lay identification of mammals and provides detailed
measurements, dental formulas and skull illustrations. The eastern grey squirrel (Sciurus
) is described as a “large tree squirrel” with three colour forms (grey
intermediate and black); the grey form is most common on Vancouver Island. A range
map shows two introduced populations in British Columbia in the Fraser Valley
(introduced to Stanley Park in the 1920’s) and Victoria (introduced in the 1960’s).
Unfortunately, there are no habitat descriptions in this guide.
Nicolas, K. 2002. Personal communication. Professional Ecological Services, Victoria,

Most of the squirrel comp laints Nicolas receives are related to squirrel denning in
buildings. She recommends excluding grey squirrels from buildings and if no young are
present, one way doors allow the squirrels to leave but not return. Bird feeders attract
grey squirrels and feeders should be removed if squirrels are a problem. Grey squirrels
are “Schedule C” animals which means that under the Wildlife Act, they can be captured
or killed anywhere in the province and at any time. Rodenticides such as Warfarin are not
recommended for dealing with problem squirrels in buildings. The squirrels either eat a
sublethal dose and will never eat the poison again or they eat a lethal dose and then die
and decompose on site. If Warfarin is used outside, it must be used in a locked, tamper-
proof bait station that is anchored to the ground.

Nixon, C. M., M. W. McClain, and R. W. Donohoe.
1975. Effects of hunting and
mast crops on a squirrel population. Journal of Wildlife Management 39(1):1-25.
Nixon et al. studied the population densities of grey squirrels (Sciurus carolinensis) and
fox squirrels (Sciurus niger) over 10 years to determine the impact of hunting and
hickory mast crops. Hunting kills were related to the density of the squirrel populations
prior to the hunt and the amount of “total gun- hours“. Squirrel populations increased in
years with larger mast crops the previous fall. In years when populations declined,
squirrels repopulated the area from adjacent forests.
Okubo, A., P. K. Maini, M. H. Williamson and J. D. Murray. 1989. On the spatial
spread of the gray squirrel in Britain, UK. Proceedings of the Royal Society of London
Series B Biological Sciences 238 (1291): 113-126.
Authors' abstract: We present a diffusion-competition model to describe the interaction
between the externally introduced grey squirrel and the indigenous red squirrel in Britain.
We estimate the model parameters from field data. Solution of the model predicts waves
of grey squirrel invasion with speed of invasion typical of that observed in the field.
Numerical solution of the model on a two-dimensional domain gives population
distributions qualitatively similar to those observed. We suggest that competition alone
could account for the observed displacement of the red squirrel by the grey in large
regions of Britain. The solutions are qualitatively similar to those for a single species
spreading in the absence of competition. The quantitative difference is because
competition slows down the speed of advance of the invading species.
Oregon Department of Fish and Wildlife. 2001. Backgrounder: Nonnative wildlife in
November 11, 2002
This public education brochure provides information on the impacts and control options
available to prevent the spread and minimize the impact of invasive species. The
information can be readily applied to Garry oak ecosystems. The native range of eastern
grey squirrels is described as "eastern North America from southern Canada to Florida
and east to the Great Plains". The brochure provides details on the squirrels current global
distribution. Grey squirrels were first introduced to Oregon in 1919 and have been
repeatedly released to the state since that time. Eastern grey squirrels have displaced
native western grey squirrels and in Washington, eastern grey squirrels are suspected of
causing a decline in native Douglas squirrels. Western grey squirrels are not native to
British Columbia and Douglas squirrels are found in the Fraser Valley, Cascade and
Coast Mountains but not within the main range of Garry oak ecosystems. The brochure
outlines how to ecologically and humanely dispose of trapped invasive mammals.
Humane euthanasia options listed are carbon dioxide, cervical dislocation, decapitation,
gunsho t to the head and barbiturates administered by veterinarians.
Penner, R., G. E. E. Moodie and R. J. Staniforth. 1999. The dispersal of fruits and
seeds of Poison-ivy, Toxicodendron radicans, by Ruffed Grouse, Bonasa umbellus, and
squirrels, Tamiasciurus hudsonicus and Sciurus carolinensis. Canadian Field Naturalist
113 (4): 616-620.
Authors' abstract: A study was conducted to determine the dispersal potential of seeds
and fruits of Poison- ivy (Toxicodendron radicans (L.) Rydb.) by mammals and birds in a
study plot near Stonewall, Manitoba, Canada. Ruffed Grouse (Bonasa umbellus) and Red
Squirrels (Tamiasciurus hudsonicus) and Grey Squirrels (Sciurus carolinensis) were the
most common visitors to feeders containing fruits and to fruit-bearing plants. Squirrels
acted as seed predators by removing the exocarps and mesocarps from fruits and eating
the seeds. However, they often dropped individual fruits or entire infructescences that
they had been carrying to dining or caching sites and because of this the y were effective
dispersal agents for the seeds. Ruffed Grouse behaved as frugivores by eating the fruits
and excreting intact seeds. Germination in seeds extracted from grouse faeces was not
significantly different from seeds from fruits taken directly from the plants. Germination
of seeds from within intact fruit was higher but, not significantly, than that from seeds
from which the exocarps and mesocarps had been removed. These results show that the
fruit and seeds of Poison- ivy are food resources for Ruffed Grouse and squirrels,
respectively. Both kinds of animals are effective seed dispersal agents for seeds of this
Pigott, C. D., A. C. Newton, and S. Zammit. 1991. Predation of acorns and oak
seedlings by grey squirrel. Quarterly Journal of Forestry 85(3):173-178.
Authors’ abstract: Grey squirrels (Sciurus carolinensis Gmel.) feed on acorns while they
are still on the tree, after they have fallen, and after they have germinated and the shoot is
beginning to grow. A single squirrel removes large numbers of acorns from the ground at
a rate of 60-80 acorns h-1. Some are consumed immediately, but most are buried in
caches. Adult grey squirrels bite a small hole in the pericarp and excise the radicle of the
embryo of every acorn they bury. This prevents germination, so that the acorn is
effectively destroyed. Young squirrels initially bury acorns undamaged but learn to
excise the radicle, probably during their first winter. The removal of acorns and their
subsequent destruction, and the destruction of seedlings, are shown effectively to prevent
regeneration of oak, at least in limited areas below gaps in the canopy.
Riege, D. A. 1991. Habitat specialization and social factors in distribution of red and
gray squirrels. Journal of Mammalogy 72 (1): 152-162.
Author's abstract: The spatial distribution, habitat specialization, use of food supply, and
interspecific behavior within coexisting populations of red squirrels (Tamiasciurus
) and gray squirrels (Sciurus carolinensis) and the social organization of red
squirrels were examined in a 10.2-ha mixed forest in northern Wisconsin [USA] during
June 1974-March 1976. Habitat specialization, not interspecific aggression, determined
differences in distribution of red and gray squirrels. Distribution and abundance of each
species were related to production of principal seed foods. Population densities of red
squirrels were highest in fir (Abies)-cedar (Thuja) cover and in pine (Pinus) cover in
months following high production of cones. Sighting densities of gray squirrels were
highest in mature cover of maple (Acer)-oak (Quercus) throughout the year and were
correlated with the tree size of red oak (Quercus rubra). Both species consumed seeds of
maple, oak, and hazel (Corylus); red squirrels also fed on conifer seeds. Interspecific
aggression between red and gray squirrels was rare. Adult red squirrels usually
established territories defended solely against conspecifics. Territories were less stable
than those found in western conifer forests.
Romanach, S. S. and D. J. Levey. 2000. An experimental test of the predator satiation
hypothesis: At what level might it apply?. Florida Scientist 63 (1): 1-7.
Authors' abstract: The Predator Satiation Hypothesis posits that synchronous masting of
fruits or nuts will maximize the probability of satiating local seed predators, allowing
some seeds to escape predation and germinate. Although the hypothesis is usually applied
at the population level to explain synchronous reproduction of many individuals, it also
might apply at the individual level. In fact, if individual trees were able to satiate local
predators, it would reduce selection for synchronous reproduction at the population level.
We tested whether individual laurel oaks, Quercus hemisphaerica, could satiate their
acorn predators. We simulated mast conditions by adding many acorns under the
canopies of some tress, while adding few to other, non- mast trees. We then monitored the
rate of acorn removal from both mast and non- mast trees. We predicted that non- mast
trees would have a higher rate of acorn removal because they would not be able to satiate
the major seed predator at our study site, the gray squirrel, Sciurus carolinensis. The
results did not support our prediction; we found no difference in the removal rate of
acorns from mast and non- mast trees. This may be attributable to two characteristics of
our study site: the unusually high density of gray squirrels during the year of our study,
and the size of Q. hemisphaerica trees at the site, which may have been too small to
produce enough acorns to satiate such a large number of seed predators. We conclude
that the Predator Satiation Hypothesis is most likely to find support at the level of a
population, not at the level of individual trees. Predator satiation appears to be a
population level phenomenon, with benefits to individual trees.
Rosell, F. 2001. Effectiveness of predator odors as gray squirrel repellents. Canadian
Journal of Zoology 79 (9): 1719-1723.
Author's abstract: The ability of gray squirrels (Sciurus carolinensis) to discriminate
between different predator odors and the use of predator odors to deter gray squirrels
from foraging on plants have not been previously investigated. To test the hypothesis that
predator scent decreases foraging, I investigated the effect of such scent on consumption
of butternuts (Juglans cinerea) in the field. Results showed that (i) red fox (Vulpes
) scent was significantly more effective than either a control or human scent; (ii)
raccoon (Procyon lotor) scent was significantly more effective than white-tailed deer
(Odocoileus virginianus) scent (but only after 7-9 h); (iii) red fox scent was not
significantly more effective than raccoon scent; and (iv) human scent was not
significantly more effective than the control. The utility of predator odors in controlling
damage by gray squirrels should be explored.
Sheail, J. 1999. The grey squirrel (Sciurus carolinensis)-A UK historical perspective on
a vertebrate pest species. Journal of Environmental Management 55 (3): 145-156.
Author's abstract: The paper reviews from archival sources the experience gained by the
UK Agriculture Departments in combating the damage caused by an alien species, the
grey squirrel. Insights are provided into the circumstances and significance of the Grey
Squirrels Order, 1937, wartime regulations, the free cartridges and tail-bonus schemes
and grey squirrels (warfarin) Order of 1973. At times pro-active, policy was more usually
driven by the need of Ministers to be seen responding to pressure from farming and
forestry, as communicated through such powerful political figures as the Prime Minister
himself, Harold Macmillan. Such instances of debate as to the optimal level of pest
regulation afforded opportunity not only for scientific study, but for scientists themselves
to participate in discussion as to the weight to be given in policy-making to the
knowledge, understanding and powers of prediction thereby gained.
Short, M. J. and J. C. Reynolds. 2001. Physical exclusion of non-target species in
tunnel-trapping of mammalian pests. Biological Conservation 98 (2): 139-147.
Authors' abstract: We developed and tested physical excluders to prevent non-target
animals from entering tunnels containing spring traps intended to kill a range of small (<2
kg) mammalian pest species. In field trials over 82,954 trap-nights, excluders did not
significantly decrease stoat (Mustela erminea) or weasel (Mustela nivalis) capture rates,
but did substantially reduce the capture rate of larger target species, notably grey squirrels
(Sciurus carolinensis) and rats (Rattus norvegicus). Excluders virtually eliminated
capture of hedgehogs (Erinaceus europaeus) - a legally protected species. By inference,
larger protected species (polecat Mustela putorius, pine marten Martes Martes, otter
Lutra lutra and wild cat Felis sylvestris) would be excluded, as would mink (Mustela
), a legitimate target species. These excluders should be advocated where there is a
real risk of catching protected species. However, because excluders compromise utility,
we recommend that their use should remain discretional unless clearly preferable
alternative methods to manage target pest species are developed.

Sieving, K. E and Wilson, M. F.
1998. Nest predation and avian species diversity in
northwestern forest understory. Ecology. 79(7):2391-2402.

Sieving and Wilson studied the impact of nest predation by constructing open-cup nests
and placing them in deciduous and coniferous forests in southeast Alaska and western
Canada. One of the main nest predators was the red squirrel (Tamiasciurus hudsonicus)
especially in coniferous forests. The authors suggest that nest predation may play a role
in habitat selection by birds and species diversity.
Steele, M. A., C. L. Z. Hadj and J. Hazeltine. 1996. Caching and feeding decisions by
Sciurus carolinensis: Responses to weevil- infested acorns. Journal of Mammalogy 77
(2): 305-314.
Authors' abstract: We tested the caching and feeding responses of gray squirrels (Sciurus
) to acorns of three species of oaks (Quercus alba, Q. palustris, and Q. rubra)
infested with weevil larvae (Curculio). Experiments were designed to test the primary
hypothesis that squirrels selectively cache sound acorns and the secondary hypothesis
that such response may be due to increased perishability resulting from infestation. In an
open, suburban oak (Quercus) forest in northeastern Pennsylvania, we presented free-
ranging animals with whole, infested acorns, whole, noninfested acorns, and noninfested
acorns from which the pericarp (shell) was removed to increase perishability. Squirrels
cached significantly (2035%) more of whole, intact acorns of red oak, dispersed these
acorns significantly greater distances before caching them, and consumed shelled and
infested acorns. Squirrels showed a similar response to acorns of pin oak, but ate
significantly more of both infested and noninfested acorns of white oak. Squirrels also
were observed to consume weevil larvae in gt 76% of all trials with infested acorns.
These results indicate that squirrels can distinguish between infested and noninfested
acorns, that they often selectively cache sound acorns, and that weevils represent a
significant dietary supplement for squirrels. We also suggest that gray squirrels may exert
a strong influence on the dispersal of oaks by selecting viable seeds for storage.
Steele, M. A., T. Knowles, K. Bridle and E. L. Simms. 1993. Tannins and partial
consumption of acorns: Implications for dispersal of oaks by seed predators. American-
Midland-Naturalist 130 (2): 229-238.
Authors' abstract: A common assumption in studies of seed predation is that seeds
survive attack and are dispersed only when animals fail to find seeds, drop undamaged
seeds or fail to recover seeds after they are cached. This study, however, suggests that
many acorn consumers consistently eat only a portion of the cotyledon of several species
of acorns and thereby permit embryo survival. Several vertebrates (gray squirrels
(Sciurus carolinensis), common grackles (Quiscalus quiscula) and blue jays (Cyanocita
)) were observed to consume only 30-60% of the cotyledon from the basal portion
(cap end) of willow oak (Quercus phellos) acorns. Gray squirrels exhibited a similar
preference for the basal end of acorns of several other species of red oaks (Q. rubra, Q.
laevis, Q. nigra, Q. palustris
and Q. coccinea) from a wide geographic region. In
addition, acorn weevil larvae (Curculio sp.) were observed significantly (gt 35%) more
often in the basal portion than in the apical end of Q. alba acorns. Chemical analyses of
acorns from two tree species revealed that the concentration of protein-precipitable
phenolics (primarily tannins) was 12.5% (Q. phellos) and 84.2% (Q. laevis) higher in the
apical portion of the seeds where the embryo is located. Moreover, germination
experiments revealed equal or greater germination frequencies for partially consumed
acorns than for intact acorns. We suggest that the higher tannin levels may render the
apical portion less palatable, and thereby increase the probability of embryo survival after
attack by seed consumers.
Steele, M. A., P. D. Smallwood, A. Spunar and E. Nelsen. 2001. The proximate basis
of the oak dispersal syndrome: Detection of seed dormancy by rodents. American-
Zoologist 41 (4): 852-864.
Authors' abstract: Previously we have shown how a range of physical and chemical
characteristics of acorns influences the behavioral decisions of food-hoarding rodents
which in turn affects the dispersal, establishment and spatial arrangement of oaks. One
such behavior involves the selective caching of acorns of red oaks (subgenus:
Erythrobalanus) over those of white oaks (Quercus) because of reduced perishability that
results from delayed germination of acorns in the red oak group. In this study, we sought
to identify the specific proximate cues (visual and olfactory) that eastern gray squirrels
(Sciurus carolinensis) use when making these decisions. In two series of field
experiments, we presented individual, free-ranging animals with pairs of experimentally
altered acorns (that differed with respect to a single chemical or visual characteristic) and
recorded their feeding and caching responses. Squirrels cached artificial acorns with
pericarps (shells) of red oak acorns and ate those with shells of white oak regardless of
the internal chemical composition of either type of acorn. Only when the shells of
artificial acorns were first soaked in acetone (to remove potential chemical odors) did
animals eat artificial acorns made with the shells of red oak acorns. Squirrels also ate
one-year old red oak acorns that had broken dormancy, even when they exhibited no
signs of germination. We argue that a chemical cue in the shell of acorns is important in
the detection of seed dormancy and the decision to cache acorns, and that such a cue
might ultimately contribute to the differential dispersal of red and white oaks by rodents.
Stiles, E. W. and E. T. Dobi. 1987. Scatterhoarding of horse chestnuts by eastern gray
squirrels. Bulletin New Jersey Academy of Science 32 (1): 1-4.
Authors' abstract: The scatterhoarding behavior shown by eastern gray squirrels (Sciurus
) is well known (Brown ad Yeager, 1945; Schorger, 1949), but few
quantitative studies of the movements of seeds from predispersal sites under the parent
tree to scatterhoard locations are available (Cahalane, 1942; Sork and Boucher, 1977;
Stapanian and Smith, 1978, 1984). Eastern gray squirrels are a primary dispersal agent
for many large seeded, canopy trees in the eastern deciduous forest (Smith and Follmer,
1972). The objective of this study was to examine scatterhoarding behavior by squirrels
and measure distances seeds were carried from the parent tree. We also suggest a pattern
of seed selection by squirrels.
Stirling, D. 2002. Personal communication. Birder, Victoria, BC. November 13, 2002.
Stirling has noticed a connection between the introduction of small mammals and the
increase in populations of owls and hawks. Before house mice, rats, grey squirrels and
rabbits were introduced in the early 1960s, there were very few small mammals on
Vancouver Island (only Townsend’s vole, deer mouse and red squirrel). Before the
mammals were introduced, there were also very few great horned and barred owls. Now,
great horned and barred owls are very common and the introduced mammals make good

Stone, W. B., J. C. Okoniewski and J. R. Stedelin. 1999. Poisoning of wildlife with
anticoagulant rodenticides in New York. Journal of Wildlife Diseases 35 (2): 187-193.
Authors' abstract: From 1971 through 1997, we documented 51 cases (55 individual
animals) of poisoning of non-target wildlife in New York (plus two cases in adjoining
states) (USA) with anticoagulant rodenticides-all but two of these cases occurred in the
last 8 yrs. Brodifacoum was implicated in 80% of the incidents. Diphacinone was
identified in four cases, bromadiolone in three cases (once in combination with
brodifacoum), and chlorophacinone and coumatetralyl were detected once each in the
company of brodifacoum. Warfarin accounted for the three cases documented prior to
1989, and one case involving a bald eagle (Haliaeetus leucocephalus) in 1995. Secondary
intoxication of raptors, principally great horned owls (Bubo virginianus) and red-tailed
hawks (Buteo jamaicensis), comprised one- half of the cases. Gray squirrels (Sciurus
), raccoons (Procyon lotor) and white-tailed deer (Odocoileus virginianus)
were the most frequently poisoned mammals. All of the deer originated from a rather
unique situation on a barrier island off southern Long Island (New York). Restrictions on
the use of brodifacoum appear warranted.
Teangana, D. O., S. Reilly, W. I. Montgomery and J. Rochford. 2000. Distribution
and status of the Red Squirrel (Sciurus vulgaris) and Grey Squirrel (Sciurus carolinensis)
in Ireland. Mammal Review 30 (1): 45-56.
Authors' abstract: The distributions of the Red and Grey Squirrel were surveyed in
Northern Ireland and the Republic of Ireland between 1994 and 1996. Survey methods
differed between the two studies. In the former, all suitable habitat, of at least 15 ha, was
inspected for species presence or absence. In the Republic, data were gathered through
questionnaires to governmental and independent wildlife bodies. The combined results
indicate that the Red Squirrel remains widespread and locally abundant, and is present in
all but two counties. The Grey Squirrel is now more widespread than ever before, and can
be found in 22 of the 32 counties. Its range expansion has varied from 0 km/yr to an
estimated 13.4 km/yr, as various geographical features, principally rivers, have hindered
its progress in certain directions.
Vandruff, L. W. and R. N. Rowse. 1986. Habitat association of mammals in Syracuse,
New York, USA. Urban Ecology 9 (3-4): 413-434.
Authors' abstract: A 2- year study of the mammals in Syracuse, NY revealed the presence
of 17 non-domestic species. Of the 13 species trapped in 20 greenspaces (Parks,
greenbelts, private woodlots, etc.), white- footed mice (Peromyscus spp.), meadow voles
(Microtus pennsylvanicus) and gray squirrels (Sciurus carolinensis) comprised 65% of
the 1040 captures from 13344 functional trapnights of effort. Species richness ranged
from 3 to 9 species captured in the greenspaces that varied in size from 2 to 22 ha. Three
interspecific associations were identified, but several species were associated with similar
habitat features. Using Spearman's rank correlation (univariate) and canonical correlation
(multivariate), capture success of each species and various combinations were correlated
with one or more of 31 physical, biotic or cultural variables obtained from on-site
measurements, aerial photographs, and Bureau of Census reports. Generally, variables
measured from aerial photographs accounted for more of the variability in mammal
abundance among areas than did detailed measurements of on-site physical or biotic
conditions. Area of water, area of grass or field, area of pavement or gravel, and total
greenspace often were significant, whereas specific characteristics of a vegetative type
such as size-class of trees, diversity of herb layer, or percentage of canopy closure in the
understory had little effect on the mammalian community. Mammals that can exist in
urbanized areas apparently respond to the mosaic of habitats and land uses in the general
area rather than those conditions found within specific greenspaces.
Wauters, L. A., J. Gurnell, I. Currado and P. J. Mazzoglio. 1997. Grey squirrel
Sciurus carolinensis management in Italy-squirrel distribution in a highly fragmented
landscape. Wildlife Biology 3 (2): 117-124.
Authors' abstract: American grey squirrels Sciurus carolinensis introduced to northern
Italy in 1948 have caused damage to commercial poplar plantations and have replaced the
native red squirrel Sciurus vulgaris from most of the 350 km-2 of the Piedmont Po-plain
they currently occupy. In order to plan a control programme aiming to stop grey squirrels
from further spreading and to decrease their numbers the current distribution and
population size in the highly fragmented landscape of the Po-plain were studied. The
probability of finding grey squirrels in woodland fragments increased with habitat quality
(diversity of trees producing large, consumable seeds), woodlot size and the proportion of
poplar. Adding isolation variables did not improve the fit of the logistic regression model
that predicted squirrel presence. The density of squirrel dreys, an index of population
density, in the large Stupinigi forest also increased with tree species diversity. An
estimate of the minimum population size for all woodlots assessed for squirrel presence
was 1,260 animals in the summer of 1996. This extrapolates to a total of ca 2,500 grey
squirrels in Piedmont. Grey squirrels continue to increase their range and are getting
close to the continuous mixed forests of the pre-Alps and to large hazel plantations.
Control measures to stop the spread of grey squirrels, and eventually to eradicate them,
should be implemented immedia tely.
Wauters, L. A., J. Gurnell, A. Martinoli and G. Tosi. 2001. Does interspecific
competition with introduced grey squirrels affect foraging and food choice of Eurasian
red squirrels? Animal Behaviour 61 (6): 1079-1091.
Authors' abstract: Grey squirrels, Sciurus carolinensis, introduced from North America,
have replaced red squirrels, S. vulgaris, over much of Britain and parts of north Italy, but



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