Huynh, H.M., Bertolino, S., Lurz, P.W.W., Koprowski, J.L., Williams, G.R., Thompson, C.W., McAlpine, D.F

Bertolino, S.

Huynh, H. M.

Koprowski, J. L.

Lurz, P. W. W.

McAlpine, D. F.

Thompson, C. W.

Williams, G. R.

English

The eastern gray squirrel, Sciurus carolinensis, is one of the world’s most recognized sciurids and a highly successful human commensal. Historically restricted to eastern North America, gray squirrel populations are now established in Italy, U.K., South Africa, and Australia, and squirrels continue to expand their geographic range globally. Successful introductions of S. carolinensis often result in significant negative impacts on native ecosystem integrity. As a result, countries have devised and implemented unique pest management strategies to reduce or eradicate S. carolinensis populations, but with differing levels of success. We review accounts of historical global introductions of S. carolinensis, discuss its invasive biology and impacts in non-native habitats, and recommend specific management strategies that should successfully curtail establishment of this species in non-native habitats

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The even darker side of the eastern gray squirrel (Sciurus carolinensis): a review of global introductions, invasion biology, and pest management strategies

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8th European Vertebrate Pest Management Conference Julius-Kühn-Archiv, 432, 2011 31 The even darker side of the eastern gray squirrel (Sciurus carolinensis): a review of global introductions, invasion biology, and pest management strategies Huynh, H.M.1,2, Bertolino, S.3, Lurz, P.W.W.4, Koprowski, J.L.5, Williams, G.R.6, Thompson, C.W.1, McAlpine, D.F.2 1Department of Biological Sciences, Texas Tech University, Lubbock, TX, 79409, USA, howard.huynh@ttu.edu 2Department of Natural Science, New Brunswick Museum, Saint John, NB, E2K 1E5 Canada  3University of Turin, DIVAPRA Entomology and Zoology Via L. da Vinci 44, 10095 Grugliasco (TO), Italy 4Lurzengasse 3, D-97236 Randersacker, Germany 5Wildlife Conservation and Management, School of Natural Resources and the Environment, 306 Biological Sciences East, University of Arizona Tucson, AZ, 85721, USA  6Department of Biology, Dalhousie University, Halifax, NS, B3H 4J1, Canada  DOI: 10.5073/jka.2011.432.012 Abstract The eastern gray squirrel, Sciurus carolinensis, is one of the world’s most recognized sciurids and a highly successful human commensal. Historically restricted to eastern North America, gray squirrel populations are now established in Italy, U.K., South Africa, and Australia, and squirrels continue to expand their geographic range globally. Successful introductions of S. carolinensis often result in significant negative impacts on native ecosystem integrity. As a result, countries have devised and implemented unique pest management strategies to reduce or eradicate S. carolinensis populations, but with differing levels of success. We review accounts of historical global introductions of S. carolinensis, discuss its invasive biology and impacts in non-native habitats, and recommend specific management strategies that should successfully curtail establishment of this species in non-native habitats.  Keywords: establishment, introduction, management, non-native, Sciurus carolinensis G. Introduction The eastern gray squirrel (Sciurus carolinensis G.) is a highly adaptable arboreal sciurid native to eastern North America (Flyger, 1999). It is also a successful human commensal, and has established populations in non-native habitats around the world as a result of introductions by people (Bertolino, 2009). Here, we review its historical introductions, comment on why it has been such a successful invasive species, and recommend possible strategies and plans for effectively managing introduced populations of this species.  Materials and Methods Historical accounts from publications and reports were reviewed for data pertaining to S. carolinensis introductions around the world. Life history information was used to make inferences on the invasive species biology of gray squirrels, and to determine why they are such successful alien species. Current management plans were also reviewed to determine what elements of control were most effective.  Results and Discussion Introductions of S. carolinensis into non-native habitats around the world have occurred since the early 1800s. In North America, regional introductions were made into previously unoccupied Canadian provinces (e.g., Nova Scotia; Huynh et al., 2010) and numerous western U.S. states, while introductions also occurred in South Africa (Davis, 1950) and Australia (Peacock, 2009). The U.K. (Lloyd, 1983) and Italy (Currado et al., 1987) have had multiple introduction events associated with the successful establishment of S. carolinensis. Hence, it appears that successful establishment of S. carolinensis is partly dependent on high propagule pressure generated by repeated introductions by people.  Trophically, gray squirrels are ecological generalists. Their highly adaptable nature in terms of resource exploitation provides them with intrinsic advantages that promote population establishment and growth. For example, though S. carolinensis primarily inhabit broad-leaved, mixed deciduous woodlands with mast species, they are able to thrive on food sources found in conifer-dominated stands (Koprowski, 1994). Such adaptable foraging behavior on the part of S. carolinensis can significantly increase survival and reproductive success, especially in the context of interspecific interactions with native species (e.g., competition – Gurnell et al., 2004; disease transmission – Sainsbury et al., 2000).  8th European Vertebrate Pest Management Conference 32 Julius-Kühn-Archiv, 432, 2011 Though the availability of trees (mast, shelter) appears to be a limiting factor in restricting population expansion, the ability of S. carolinensis to thrive in human-modified landscapes facilitates the species establishment in introduced environments. Urban areas in particular often have high population densities of S. carolinensis and can function as refugia and patch sources in dispersal dynamics.  Gray squirrels are often considered attractive and benign by local communities, which may enhance the probability of successful establishment. Indeed, human enamorment with gray squirrels appears to be an important factor in determining the fate of an introduced population – the novelty of introduced S. carolinensis along with the associated emotional attachment generated by their charisma may function as intractable hindrances to development and proper implementation of pest management and eradication programs (e.g., Bertolino et al., 2000).  Effective management plans for introduced gray squirrels should include: detection and monitoring of introduced S. carolinensis (Tattoni et al., 2006); understanding the ecological interactions and impacts of S. carolinensis in non-native habitats (Gurnell et al., 2004); collating spatial data on the environment (i.e., landscape structure, connectivity and composition; Lurz et al., 2001); and eradication of potential founders before population establishment (Tattoni et al., 2006).  References Bertolino S 2009 Animal trade and non-indigenous species introduction: the world-wide spread of squirrels. Diversity and Distributions 15: 701-708 Bertolino S, Currado I, Mazzoglio PJ, Amori G 2000 Native and alien squirrels in Italy. Hystrix 11: 65-74 Currado I, Scaramozzino PL, Brussino G 1987 Note sulla presenza dello Scoiattolo grigio (Sciurus carolinensis Gmelin, 1788) in Piemonte (Rodentia: Sciuridae). Annali della Facoltà di Scienze Agrariedella Università degli Studi di Torino 14: 307-331 Davis DHS 1950 Notes on status of the American grey squirrel (Sciurus carolinensis Gmelin) in the south-western Cape (South Africa). Journal of Zoology 120: 265-268 Flyger V 1999 Eastern gray squirrel (Sciurus carolinensis). In: Wilson DE, Ruff S (eds.) The Smithsonian Book of North American Mammals. p. 451-453, Smithsonian Institution Press, Washington DC, USA Gurnell J, Wauters LA, Lurz PWW, Tosi G 2004 Alien species and interspecific competition: effects of introduced eastern grey squirrels on red squirrel population dynamics. Journal of Animal Ecology 73: 26-75 Huynh HM, Williams GR, McAlpine DF, Thorington Jr. RW 2010 Establishment of the eastern gray squirrel (Sciurus carolinensis) in Nova Scotia, Canada. Northeastern Naturalist 17: 673-677 Koprowski JL 1994 Sciurus carolinensis. Mammalian Species 480: 1-9 Lloyd HG 1983 Past and present distribution of red and grey squirrels. Mammal Review 13: 69-80 Lurz PWW, Rushton SP, Wauters LA, Bertolino S, Currado I, Mazzoglio P, Shirley MDF 2001 Predicting grey squirrel expansion in North Italy: a spatially explicit modelling approach. Landscape Ecology 16: 407-420 Peacock DE 2009 The grey squirrel Sciurus carolinensis in Adelaide, South Australia: its introduction and eradication. The Victorian Naturalist 126: 150-155 Sainsbury AW, Nettleton P, Gilray J, Gurnell J 2000 Grey squirrels have high seroprevalence to a parapoxvirus associated with deaths in red squirrels. Animal Conservation 3: 229-233  Tattoni C, Preatoni DG, Lurz PWW, Rushton SP, Tosi G, Bertolino S, Martinoli A, Wauters LA 2006 Modelling the expansion of a grey squirrel population: implications for squirrel control. Biological Invasions 8:  1605-1619  

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The even darker side of the eastern gray squirrel (Sciurus carolinensis): a review of global introductions, invasion biology, and pest management strategies

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