Nest Site Fidelity of Northern Map Turtles, Graptemys geographica

Abstract

Northern map turtles (Graptemys geographica) are a species of conservation concern with a limited distribution in Pennsylvania. We examined nest site fidelity of G. geographica along the Juniata River at Mount Union, the largest reported nesting area in the commonwealth. Nesting habitat included a mitigation area bordering a highway, partitioned by a turtle exclusion fence, and an adjacent pile of coal tailings. A linear grid along the turtle fence allowed us to determine distances between nests of individual females. Our results indicate that female G. geographica at Mount Union exhibit nest site fidelity, as the frequency distribution of distances between nests of individual females was positively skewed, and distances between nests (both within and among seasons) were smaller than distances between randomly selected pairs of nests from different individuals. Females placed different clutches of eggs as close together as 0.30 m. Within-season (first and second clutch) internest distances were significantly smaller than internest distances among years, which increased over time. We also attached radio transmitters to a sample of adult females following nesting to determine the extent of riverine migrations, as long-distance nesting migrations are associated with fidelity to particular nesting sites. Following nesting, 2 females remained in the river near the Mount Union nesting habitat and 3 females moved downstream 4.3–5.6 km, yet all of the turtles returned to their previous nesting areas the following summer. Nest site fidelity can benefit map turtles if the habitat remains stable, results in high nest survivorship, and produces high-quality hatchlings, yet the behavior may be detrimental if it exposes turtles to significant risks such as road mortality or environmental contaminants. Our results indicate that maintaining long-term nesting habitat and ensuring suitable river quality at Mount Union may be essential for the conservation of G. geographica in central Pennsylvania.