386 Northeastern Naturalist Vol. 18, No. 3 Evidence of Multiple Annual Litters in Glaucomys sabrinus (Northern Flying Squirrel) Matthew J. Smith1,*, Graham J. Forbes2, and Matthew G. Betts3 Abstract- Recently, Patterson and Patterson (2010) documented a single Glaucomys sabrinus (Northern Flying Squirrel) having two litters in a single year in southern Ontario, Canada. We confirm this record and provide evidence for two new observations; 1) Northern Flying Squirrels will attempt a second litter after raising a successful first litter; and 2) Northern Flying Squirrels can be lactating and pregnant at the same time. We also present data on the frequency of polyestry in a single year. In 2008, 3 of 10 radio-collared flying squirrels in southern New Brunswick, Canada attempted two litters. The first litter was born in early June, and the second litter in mid-August. Our data suggest that polyestry in Northern Flying Squirrels may be relatively common in some years. Annual fecundity is an important demographic parameter in the development of population models. Glaucomys sabrinus Shaw (Northern Flying Squirrel) has been suggested by many authors to be an indicator or keystone species for mature forest (Carey 2000, Ritchie et al. 2009, Smith and Person 2007, Vernes 2004), with a relatively low annual fecundity (mean = 2.5, SD = 0.19) (Villa et al. 1999). Accurate information about species’ reproductive potential is clearly fundamental to understanding their population dynamics and responses to environmental change. Unlike Glaucomys volans L. (Southern Flying Squirrel), which are well known to be polyestrous (Reynolds et al. 2009) and may have two litters in one season (Sollberger 1943), Northern Flying Squirrels are reported to have one litter per year (Davis 1963, Wells-Gosling and Heaney 1984); however, other authors have suggested that 2 or even 3 litters may be possible (Seton 1929). Also, numerous trapping studies have found evidence of late-fall breeding (i.e., populations with lactating females and recently weaned juveniles; Ransome and Sullivan 2003, Raphael 1984, Vernes 2004, Witt 1991), but these observations may be the result of delayed breeding rather than a second litter (Vernes 2004). Polyestry in Northern Flying Squirrels has recently been confi rmed after it was detected in a nest-box study in southern Ontario, Canada (Patterson and Patterson 2010). However, Patterson and Patterson (2010) only provided evidence that the first litter was successful through nine days post-partum, and it is possible that the first litter failed (i.e., was not successfully weaned) before the second breeding attempt. Confusion regarding a species’ reproductive potential can lead to significant errors in population models. A recent paper by Smith and Person (2007) used demographic data that assumed Northern Flying Squirrels have one litter and an annual fecundity of 2 (1 SD). They predicted that populations in small patches isolated by forest harvesting may face local extinctions. These viability predictions may be inaccurate if some females have additional litters, thereby compensating for low survival rates. We investigated the frequency of multiple litters by attaching radio collars (Holohil Model PD-2C, <4.5 g) to 10 lactating females in Albert and Kings County, in southern New Brunswick, Canada (45°37'01"N, 65°01'50"W; elevation range = 50–360 m). This area receives an average of 2719 mm of snow from December to the end of March, with average snow depths for the same period of 180 mm (Environment Canada 2000). 1Fundy National Park, PO Box 1001, Alma, NB, Canada E4H 1B4. 2Faculty of Forestry and Environmental Management, PO Box 4400, 28 Dineen Drive, University of New Brunswick, Fredericton, NB, Canada E3B 5A3. 3Department of Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331. *Corresponding author - matthew.smith@ pc.gc.ca. Notes of the Northeastern Nat u ral ist, Issue 18/3, 2011 386 2011 Northeastern Naturalist Notes 387 Latitude and climate have been correlated with increased litter size in squirrels (Hayssen 2008, Lord 1960); and many studies of passerine birds have found that early spring breeding is a strong predictor of double brooding (Verboven and Verhulst 1996, but see Nagy and Holmes 2005). Shortly after attachment of transmitters, we located nest locations and climbed trees to count the number of young. We weighed all young to the nearest gram (using a 300-g Pesola scale) and assessed developmental stage based on physical characteristics (Davis 1963, Muul 1969, Villa et al. 1999). All individuals were individually marked with two Monel self-piercing tags (1005-1, National Band and Tag Co., Newport, KY). Flying squirrels were tracked from 10 May–27 November 2008. In 2008, 3 of 10 radio collared females (30%) attempted second litters (Table 1). We included only individuals for which we had checked nests for neonates in the spring and breeding condition in the fall. Females that were lactating in the spring and showed no evidence of lactating in late summer and fall were considered to have a single litter. On 17 June 2008, a pregnant female (T578) (weight: 125 g) was captured and radio collared. On 16 July, the nest tree was climbed and two young were observed (one captured: a 40-g male). On 18 July, T578 was still lactating, but visibly pregnant and very heavy (137 g). On 8 August, this same female (T578) was found dead below her nest tree with no visible signs of predation. A necropsy revealed that she was pregnant with 5 young. Total body weight of the female was 125.6 g, but the gravid uterine horns to the cervix weighed 23.3 g. The lumen of the left uterine horn contained 3 normally developing fetuses (#1 male: 4.2 g, crown–rump length = 3.5 cm; #2 male: 3.7 g, crown–rump length = 3.2 cm; #3 male: 4.2 g, crown–rump length = 3.8 cm), and the lumen of the right uterine horn contained two decomposing macerated fetuses (McBurney 2008). There was marked inflammation in the right uterine horn and mild inflammation in the left uterine horn; Staphyloccocus aureus was isolated from the affected tissue (McBurney 2008). The individual (T578) had very low weight, and fat reserves were nearly absent. The radio collar was loose, and there was no indication that this contributed to mortality. On 10 July 2008, a lactating female (T602) (weight:124 g), at least 3 years old (based on previous capture data), was captured and radio collared. On 16 July, this individual was tracked to a cavity in a living Acer rubrum L. (Red Maple) (nest height = 1.5 m), and Table 1 Timing of first and second litters for 10 Northern Flying Squirrels (Glaucomys sabrinus) tracked June to December in 2008. Multiple litters are shown in bold. M = male, F = female, and ? = unknown Litter Date nest found Average Squirrel # number (dd/mm/yyyy) # of young weight (g) Sex T980 1 20/06/2008 1 45 1F T841 1 27/06/2008 4 36 2 M/1 F/ 1 ? T518 1 02/07/2008 3 34 2 M/1F T089 1 02/07/2008 3 38 2 M/1F T510 1 07/07/2008 1 40 1 F T822 1 08/07/2008 3 48 1 M/ 2 F T271 1 09/07/2008 3 49 3 M T578 1 16/07/2008 2 40 1M/ 1 ? T578 2 08/08/2008 5 3 3 M/ 2 ? T602 1 16/07/2008 4 45 1 M/ 2 F /1? T602 2 11/10/2008 5 62 1 M/ 4 ? T560 1 30/07/2008 1 59 1 F T560 2 19/09/2008 5 17 3 M/2 F 388 Northeastern Naturalist Vol. 18, No. 3 four young were observed (1 male, 2 female, and 1 escaped prior to being sexed). Average weight of these captured young was 45 g (range: 45–46 g), and we estimated these individuals to be ≈40 days old (based on Muul 1969). On 12 August, T602 was again lactating (weight: 106 g), and was tracked on 11 October to a cavity nest in a dead Abies balsamea (L.) P. Mill. (Balsam Fir). Upon our climbing this tree, T602 exited the nest with 5 young. Only one juvenile squirrel was captured (female: 62 g). On 30 October, the radio collar of T602 was found in a tunnel 3 cm underground, likely depredated by Mustela sp. (weasel). On 29 July 2008, a lactating female (T560) weighing 105 g was captured and radio collared. The next day in a nearby trap (20 m), a female juvenile flying squirrel (T021) was also captured (weighing 59 g with grey pelage) and radio collared. The juvenile was estimated to have been born two months earlier and was near weaning age (Wells-Gosling and Heaney 1984). Both individuals were located occupying the same nest over a period of one and a half weeks. Since no other young were observed in the nest with the lactating female, we assumed that T021 was the offspring of T560. On 19 September, T560 was located in a new nest with 5 neonates (average weight: 17.4, range: 15–19 g). On 22 October, the radio collar of squirrel T560 was found under the ground in a small tunnel. This individual was assumed to be depredated by a weasel. Our study provides further evidence that Northern Flying Squirrels may have multiple litters. Other studies have assumed that juveniles captured in the fall of the year occurred after failed first litters. We have data that indicates that 30% of adult females in 2008 attempted to raise two litters. Two of these double-litter females raised the first litter to dispersal age (>60 g), before attempting a second litter. We also present the first evidence that Northern Flying Squirrels may be both lactating and pregnant at the same time. A trapping study conducted in southern New Brunswick over a four-year period (2005–2008; M. Smith, unpubl. data) reveals yearly fluctuations in the number of falllactating females and fall juveniles. Future studies should explore the proximate reasons for multiple litters, e.g., environmental factors: (climate, food supply) and individual characteristics of multiple breeders (e.g., age, weight, body condition). We are currently investigating which environmental factors are correlated with fluctuations in late summer breeding. The average spring temperatures for 2008 (April–May) indicate that it was 0.7 °C warmer than the 30-year average (Environment Canada 2000), while 2008 was a poor cone year for Picea rubens Sarg. (Red Spruce) (M.J. Smith, unpubl. data). Our observations suggest that having an additional litter is risky, with one female dying before the birth of her second litter, and the other two dying later in the fall, both likely from weasel predation. In comparison, 3 of 7 (43%) of females that had single litters died. The mean annual fecundity for the three multiple-litter females (assuming that T587 survived) was 7.3 compared to 2.5 for the single-litter females. These data indicate a much higher reproductive output for Northern Flying Squirrel than previously considered. However, due to our small sample size (n = 10), we recommend more data should be collected over multiple years to accurately estimate annual fecundity for Northern Flying Squirrels. Acknowledgments We would like to thank all of the field technicians of 2008 for their help in collecting these data: Wil Brunner, Sophie Cauvy, Heather Fleming, Kiyono Katsumata, Bryan Taylor, Jeremy Thibodeau, and Karen Tomkins. Funding for this project was provided by Parks Canada, New Brunswick Wildlife Trust Fund, Province of New Brunswick, and the Fundy Model Forest. We would also like to thank Scott McBurney at the Atlantic Veterinary College, University of Prince Edward Island for performing the necropsy. This manuscript was improved with helpful comments from Jeff Bowman, and the manuscript editor Albrecht Schulte-Hostedde. 2011 Northeastern Naturalist Notes 389 Literature Cited Carey, A.B. 2000. Effects of new forest management strategies on squirrel populations. Ecological Applications 10:248–257. Davis, W. 1963. Reproductive ecology of the Northern Flying Squirrel in Saskatchewan. M.A. Thesis. 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