Trade-offs and Vulnerability of Northern Pine Snakes (Pituophis m. melanoleucus): A Comparison of Nest-Site Selection in the Early 1980s and 2020

Female reptiles may be able to increase the fitness of offspring by selecting nest sites that are less vulnerable to human disturbances and predators, while providing an appropriate thermal and hydric environment for incubation of their eggs. Northern Pine Snakes (Pituophis melanoleucus) in the New Jersey Pinelands are the only snake in North America known to spend days digging their nests, exposing themselves to predators and people. Both nest site and the habitat selected are critical to ensuring reproductive success. Our overall objective was to determine the factors involved in nest-site selection by Northern Pine Snakes to determine trade-offs females face, and to determine whether these characteristics appear to have changed over the last 37 yr in response to human activities and habitat degradation. We compared characteristics of nest sites, random points within clearings, and random points in the surrounding forest for 42 Northern Pine Snake nests in 2020, and secondly, compared specific characteristics with those of 22 nests examined in 1983. The data indicate that (1) nest sites in 2020 were usually in soft sand, rather than in hard packed sand or in "sugar sand"; (2) sand penetration (e.g., sand density) of nests exhibited a narrow range, while random points were in sand ranging from sugar sand to hard packed sand; (3) the ground cover of nest sites was more often moss/lichen compared with other vegetation; and (4) nest sites were in more open habitats than random points within clearings or the surrounding forest. Compared to the 1980s, Northern Pine Snake nests examined in 2020 were in similar habitat conditions (intermediate sand type, open habitats, with surrounding forests), but were more often on paleodunes, deeper in forests, with higher rates of off-road-vehicle (ORV) disturbances. Females spend 2-4 d digging their nests, presumably to ensure appropriate conditions for offspring embryogenesis and to protect eggs and hatchlings. Our results indicate that, while digging, they are vulnerable to thermal stress, predation, poaching, and mortality from ORVs. Thus our results highlight the trade-off between the fitness of the nesting female and the fitness of her offspring.