Timing of nesting.—Most studies of G. insculpta populations have observed nesting activities around mid- June (e.g., Farrell and Graham 1991; Brooks et al. 1992; Kaufmann 1992). Recent studies, however, have documented nesting as early as late May (Foscarini 1994; Smith 2002). The difference in dates for the onset of nesting is likely a combination of annual weather patterns but one cannot ignore the possibility of turtles nesting earlier due to global climate change. Interestingly, the onset of nesting in G. insculpta shows little latitudinal variance. Glyptemys insculpta may be selecting the optimal thermo-period for incubation, i.e., July and August. Moreover, a reduced incubation period may decrease the probability of egg predation.
We observed a bimodal daily nesting period, with most nests constructed in early morning or mid to late evening (Fig. 2). Although morning nesting has been reported in the literature, it has been considered an aberrant behavior (Pallas 1960; Farrell and Graham 1991; Harding and Bloomer 1979). Our study corroborates previous observations that nesting is stimulated by periods of rain (Pallas 1960; Harding and Bloomer 1979). Future studies must elucidate if environmental extremes, substrate quality, or predator drive timing are causing site selection for nesting.
Movement patterns.—Turtles moved up to 3700 m to the nesting site despite occurrence of many potential, less distant nesting sites. Female G. insculpta can travel long distances to nest (Harding 1991; Quinn and Tate 1991; Saumure 2004). Although lengthy nesting migrations appear widespread in freshwater turtles (e.g., Plummer and Schirer 1975; Obbard and Brooks 1980; Morreale et al. 1984), most studies suggest a paucity of suitable nesting sites to account for the behavior. Our observations of females by-passing nesting areas used by other G. insculpta suggest a more complex explanation. Porter (1972) suggested that communal egg-laying probably occurs because a particular area is especially favorable for egg deposition and development. Thus, females may select ideal nesting sites with optimal physical conditions (Congdon et al. 1983; Morreale et al. 1984, Wilson 1998). Staging.—Turtles staged in the vicinity of the nesting site for several days prior to actually nesting. Similar observations of staging have been documented for Slider (Trachemys scripta) and Blanding’s Turtles (Cagle 1950; Congdon et al. 1983). Since staging G. insculpta tended to use unaltered habitats, they are at least partially sensitive to exogenous disturbances. This presents us with an interesting dichotomy, as anthropogenic clearings are clearly used as nesting sites. Given that the staging area represents only 0.2% of the area known to be occupied by this population, poaching or additional development therein could be catastrophic.
Nest site fidelity.—Our observations of nest site fidelity support previous accounts in Michigan (Harding 1991). Nest site fidelity may reflect a shortage of nest areas (Loncke and Obbard 1977), female selection of the best nest sites (Porter 1972; Congdon et al. 1983; Morreale et al. 1984), or innate return of females to natal nesting areas (Carr 1967).
The nesting area located in the gravel pit has changed little in at least 50 years. Local landowners confirmed that Wood Turtles have been nesting in this area throughout this duration. Regardless of whether turtles are returning to natal nesting areas, nest site fidelity in G. insculpta suggests that conservation efforts should include the identification and protection of nesting areas.
Reproductive Output.—We observed significant positive correlations between clutch size and CL, PL, and body mass (Table 3). Similarly, an Ontario study found that G. insculpta CL was positively correlated with clutch size (Brooks et al. 1992). Thus, within a population, larger Wood Turtles have larger clutches of eggs. Moreover, turtles that nested in both years of our study were significantly larger than turtles observed to nest only in one year (Table 2). Larger turtles may have increased fecundity because they can reproduce more frequently. Since G. insculpta are larger in this population than those seen further south (Daigle 1997; Walde et al. 2003), a greater proportion of females may be capable of annual reproduction.
Mean clutch sizes differed significantly between 1996 and 1997. The mean clutch size during our two-year study lies within the range of those reported from seven other populations (Table 4). Since northern populations of wood turtles are larger than those occurring further south (Daigle 1997; Walde et al. 2003), it was predicted that northern populations would also have larger clutches. Clutch size was not significantly correlated to increase in CL when compared among populations (r = 0.52, P = 0.183). However, although this is not statistically significant, the proportion of variance in clutch size explained by body size between populations is similar to that observed within our study (see Table 3). Therefore, it is likely that this non-significant result is due to a low sample size (Cohen 1992). Data from additional study locations as well as implementation of long-term studies that account for annual variability in clutch size could provide conclusive explanations for the above observations (Bury 2006; Fitch 2006).
Predation.—Mammalian predators can destroy > 80% of G. insculpta nests (e.g., Harding and Bloomer 1979; Brooks et al. 1992). Surprisingly, no mammalian predation of eggs was observed during this study despite the presence of many potential nest predators. Whether mammalian predators were naïve at exploiting this food resource (Doody et al. 2003) is subject for speculation. Incubation period.—Although the average incubation period in our study (Fig. 3) was similar to those in New Hampshire (mean = 76 days, range = 66-82; Tuttle and Carroll 1997), the range was greater for our population. Cagle (1950) documented that cooler incubation temperatures result in a greater range of hatching dates. Increased incubation periods at northern latitudes may result in lower recruitment, as insufficient time / degreedays for development may be a limiting factor (Cagle 1954; Christiansen and Moll 1973; Compton 1999). Our observations of higher nest success for nests that were constructed during the first half of the nesting season would support these conclusions.
Nest and recruitment success.—Despite the absence of mammalian predation at our study site, nest success was lower than expected. Recruitment success rates of 74 - 77% have been previously recorded for G. insculpta although incubation conditions varied. These past studies have reported on nests under nest protectors (Tuttle and Carroll 1997), ex situ (Farrell and Graham 1991) and Smith (2002), excavated nests as soon as hatchlings began to emerge to prevent depredation by dipterans. The lower recruitment success observed at our northern population may have been due to predation by insects (Walde 1998).
In addition, lower recruitment success may have resulted from insufficient time and degree days to complete incubation (Obbard and Brooks 1981; Brooks et al. 1991, 1992). This hypothesis was modeled by Compton (1999) and is supported by our observation of higher nest success for those nests laid earlier in the season.
Despite its survival advantage for some species (Carr 1952), our lack of evidence of overwintering hatchling G. insculpta is in line with most other studies (Harding and Bloomer 1979; Brooks et al. 1992; Ernst et al. 1994; Buech et al. 2004). Only one unconfirmed report of a G. insculpta hatchling successfully overwintering in the nest is known (Parren and Rice 2004). The inability of hatchling G. insculpta to over-winter in the nest probably limits the northern distribution of the species.
Conclusion and Suggestions.—Our study provides much insight into the nesting ecology of G. insculpta. A short nesting season, nest-site fidelity, and staging behavior render the species vulnerable to disturbances and/or poaching. Within a single week, > 50% of the female population at our site was present within a 200 m staging ground and the nesting site. An additional reason for protecting nesting sites is that female Wood Turtles are extremely sensitive to disturbance prior to the initiation of laying. Anthropogenic disturbances at nesting sites could cause G. insculpta to delay nesting and/or nest in less favorable habitats. Such a delay and/or movement may reduce nest survivorship, as nests constructed earlier in the nesting season had higher success rates. Additional investigation into the nesting ecology of the wood turtle, as well as how anthropogenic disturbances could influence nesting activity is warranted.
Acknowledgments.—This study was part of a larger program initiated by Société de la faune et des parcs du Québec, Parks Canada, St. Lawrence Valley Natural History Society, McGill University, and l’Université du Québec à Trois-Rivières. Funding, equipment, and personnel for this research were generously provided to the St. Lawrence Valley Natural History Society by Parks Canada, Fondation de la Faune du Québec, and Société de la faune et des parcs du Québec. We thank all those who aided this project by assisting with the fieldwork. Earlier drafts of the manuscript were improved by discussions with and/or reviews by Francis Cook, R. K. Stewart, Marcella Trembley, David Rodrigue, and Angela Walde. David Pike provided statistical insight. Portions of this manuscript were submitted in partial fulfillment of the requirements for the degree of Master of Science to the Department of Natural Resource Sciences of McGill University.