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Multiple Annual Litters in Glaucomys sabrinus (Northern Flying Squirrel)
Jesse E.H. Patterson and Stephen J. Patterson

Northeastern Naturalist, Volume 17, Issue 1 (2010): 167–169

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Multiple Annual Litters in Glaucomys sabrinus (Northern Flying Squirrel) Jesse E.H. Patterson1,* and Stephen J. Patterson2 Abstract - We provide positive documentation of multiple litters in a single year born to an individual Glaucomys sabrinus (Northern Flying Squirrel) residing in southern Ontario, Canada. The first litter, consisting of four young, was observed on May 18, 2003. The second litter, consisting of five young, was observed 15 weeks later on September 2, 2003. The individual female, identified by a unique ear-tag, established natal nests in different nearby nest boxes. Our finding suggests the Northern Flying Squirrel possesses greater population growth potential than previously thought. Debate surrounding the number of litters produced annually by Glaucomys sabrinus Shaw (Northern Flying Squirrel) was initiated when Seton (1929) suggested that, like Glaucomys volans L. (Southern Flying Squirrel), Northern Flying Squirrels might produce two or even three litters of young in a single year. Soon after, Cowan (1936) observed that, although multiple litters may be common in Southern Flying Squirrels, there was no evidence for this behavior in Northern Flying Squirrels. Accordingly, mammalogists have traditionally believed the Northern Flying Squirrel to be capable of producing only one litter per year (Wells-Gosling and Heaney 1984). The peak breeding season for Northern Flying Squirrels typically occurs from March to April throughout most of the range (Davis 1963), with litters born from May to July. In some regions, such as the Pacific Northwest forest zone (northern California through southern British Columbia), the breeding season has been observed to extend into early July (Carey 1991). Reproductively active females in late autumn and winter have been reported in some studies (Forsman et al. 1994, Ransome and Sullivan 2003, Reynolds et al. 1999, Witt 1991), as has a single winter litter (Raphael 1984). Ransome and Sullivan (2003) stated that breeding in autumn and winter may represent second litters; however, they failed to differentiate between multiple litters and late litters. Multiple litters require autumn or winter parturition to be preceded by spring parturition in the same individual, a behavior that has never before been explicitly documented for the Northern Flying Squirrel. Also of note, all previous observations of autumn and winter breeding activity have been from the Pacific Northwest forest zone, where winter snowfall typically does not either exceed 350 mm (Ransome and Sullivan 2003) or remain on the ground longer than a week (Raphael 1984). Northern Flying Squirrels preferentially construct their natal nests in tree cavities (Bakker and Hastings 2002, Holloway and Malcolm 2007). However, despite their importance to Northern Flying Squirrels, nests within tree cavities remain poorly studied due to logistical constraints. Nest boxes have often been employed to study reproductive parameters of several species of small arboreal mammals, including Northern Flying Squirrels and Southern Flying Squirrels (Althoff and Althoff 2001, Carey 2002, Fokidis and Risch 2005). Between 2002 and 2004, we deployed 266 nest boxes throughout Bruce and Grey counties in southern Ontario, Canada, as part of a larger study on Northern Flying Squirrels (Patterson 2008). This region of Canada receives an average of 4100 mm of snow annually from October through to the end of March and the average winter snow depth over the same period is 174 mm (Environment Canada 2000). The nest box design used in this study followed Sonenshine et al. (1973), except that we did not include a hinged door or wire screen at the Notes of the Northeastern Nat u ral ist, Issue 17/1, 2010 167 168 Northeastern Naturalist Notes Vol. 17, No. 1 front of the shelter. Instead, our boxes were constructed such that the top lid could be flipped up to remove animals. All nest boxes were checked twice per year, once in the spring and once again in autumn, and cursory visual nest-box inspections were conducted monthly to monitor the condition and status of the boxes. All adult females retrieved from nest boxes were uniquely marked with Monel No. 1 ear-tags (National Band and Tag Co., Newport, KY) at time of first capture. On May 18, 2003, a female Northern Flying Squirrel and four (three female, one male) approximately nine-day-old pups (following Muul 1969) were initially found occupying a nest box near Shallow Lake, ON (44o38'47"N, 81o03'47"W; elevation: 230 m). This same ear-tagged female was found again in a different, nearby nest box fifteen weeks later, on September 2, with five young (four females, one male). The young found in autumn had fully open eyes, lower incisors present, and were fully furred; thus, their estimated age was 28 days. The gestation period for the Northern Flying Squirrel is between 37 and 42 days (Muul 1969), placing the date of first copulation at about March 28 and the date of second copulation at about June 24. While previous findings have only been able to confirm late breeding activity, our observation provides the first positive documentation of multiple litters in a single year by a Northern Flying Squirrel, demonstrating that Northern Flying Squirrels are indeed capable of polyestry. Additionally, while late breeding has been reported in the subspecies G. s. oregonensis and G. s. fuliginosis, we provide the first evidence of late breeding for G. s. macrotis, the subspecies found in our study area. We have little reason, based solely on this single observation, to believe that polyestrous behaviour is prevalent in the Northern Flying Squirrels. Nonetheless, when integrated with evidence provided by Ransome and Sullivan (2003), Raphael (1984), and Witt (1991), late-autumn/winter parturition appears to be relatively common in Northern Flying Squirrels throughout their range. The possibility exists that our supplemental nest boxes acted to improve the fitness of the Northern Flying Squirrels; however, previous work has suggested that Northern Flying Squirrel populations are not limited by den-site availability, nor is population growth enhanced by nest-box supplementation (Ransome and Sullivan 2004). Our finding suggests that the Northern Flying Squirrel possesses a capacity for greater population growth potential than previously thought. We are unable to confirm the frequency of polyestry in Northern Flying Squirrels based on this single observation. Future studies are warranted into the extrinsic (i.e., ambient temperature, food resources) and intrinsic (i.e., chemosensory stimuli, hormone levels) cues of polyestry in Northern Flying Squirrels, as well as geographic variability in their reproductive parameters. Acknowledgments. We thank the Grey-Sauble Conservation Authority for allowing us access to their property, as well as Thistlewood Timber Frame Homes in Markdale, ON, for donating the lumber used to construct the nest boxes. We would also like to acknowledge the support, assistance, and editorial comments provided by J.R. Malcolm, M. Patterson, and H.C. Maddin. Further helpful criticisms were received from three anonymous reviewers and manuscript editor Thomas J. Maier. Literature Cited Althoff, D.P., and P.S. Althoff. 2001. Monitoring Southern Flying Squirrel populations with nest boxes. Ohio Journal of Science 101:2–11. Bakker, V.J., and K. Hastings. 2002. Den trees used by Northern Flying Squirrels (Glaucomys sabrinus) in southeastern Alaska. Canadian Journal of Zoology 80:1623–1633. Carey, A.B. 1991. The biology of arboreal rodents in Douglas-fir forests. USDA Forest Service General Technical Report PNW-GTR-276. 2010 Northeastern Naturalist Notes 169 Carey, A.B. 2002. Response of Northern Flying Squirrels to supplementary dens. Wildlife Society Bulletin 30:547–556. Cowan, I.M. 1936. Nesting habits of the flying squirrel Glaucomys sabrinus. Journal of Mammalogy 17:58–60. Davis, W. 1963. Reproductive ecology of the Northern Flying Squirrel in Saskatchewan. M.A. Thesis. University of Saskatchewan, Saskatoon, SK, Canada. Environment Canada. 2000. Canadian climate normals or averages 1971–2000: Wiarton, Ontario. Atmospheric Environment Service. Available online at http://www.climate.weatheroffice.ec.gc.ca/climate_normals/index_e.html. Accessed 11 July 2008. Fokidis, H.B., and T.S. Risch. 2005. The use of nest boxes to sample arboreal vertebrates. Southeastern Naturalist 4:447–458. Forsman, E.D., I.A. Otto, D. Aubuchon, J.C. Lewis, S.G. Sovern, K.J. Maurice, and T. Kaminski. 1994. Reproductive chronology of the Northern Flying Squirrel on the Olympic Peninsula, Washington. Northwest Science 68:273–276. Holloway, G.L., and J.R. Malcolm. 2007. Nest tree use by Northern and Southern Flying Squirrels in central Ontario. Journal of Mammalogy 88:226–233. Muul, I. 1969. Mating behaviour, gestation period, and development of Glaucomys sabrinus. Journal of Mammalogy 50:121. Patterson, J.E.H. 2008. Forest fragmentation effects and the cavity nest material requirements of Northern Flying Squirrels and Red Squirrels in a fragmented secondary hardwood forest region of Ontario, Canada. M.Sc.F. Thesis. University of Toronto, Toronto, ON, Canada. Ransome, D.B., and T.P. Sullivan. 2003. Population dynamics of Glaucomys sabrinus and Tamiasciurus douglasii in old-growth and second-growth stands of coastal coniferous forest. Canadian Journal of Forest Research 33:587–596. Ransome, D.B., and T.P. Sullivan. 2004. Effects of food and den-site supplementation on populations of Glaucomys sabrinus and Tamiasciurus douglasii. Journal of Mammalogy 85:206–215. Raphael, M.G. 1984. Late fall breeding of the Northern Flying Squirrel, Glaucomys sabrinus. Journal of Mammalogy 65:138–139. Reynolds, R.J., J.F. Pagels, and M.L. Fies. 1999. Demography of the Northern Flying Squirrel in Virginia. Proceedings of the Annual Conference of Southeastern Association of Fish and Wildlife Agencies 53:340–349. Seton, E.T. 1929. Lives of Game Animals. Volume 4 (Part 1). Doubleday, New York, NY. 440 pp. Sonenshine, D.E., D.G. Cerretani, G. Enlow, and B.L. Elisberg. 1973. Improved methods for capturing wild flying squirrels. Journal of Wildlife Management 37:588–590. Wells-Gosling, N., and L.R. Heaney. 1984. Glaucomys sabrinus. Mammalian Species 229:1–8. Witt, J.W. 1991. Fluctuations in the weight and trap response for Glaucomys sabrinus in western Oregon. Journal of Mammalogy 72:612–615. 1Department of Biological Sciences, University of Calgary, 2500 University Drive, Calgary, AB, Canada, T2N 1N4. 2251 Queen Street South, Suite 523, Streetsville, ON, Canada, L5M 1L7. *Corresponding author - jesse.patterson@ucalgary.ca.