Natal Philopatry in a Long-Lived Species: The Return of Reproductive River Turtles Marked and Released as Hatchlings

Abstract

Natal philopatry—the return of an animal to its place of birth to reproduce—can shape population genetics and link essential habitats across generations, yet examples from long-term mark-recapture studies are rare. In this study, we observed 136 nests of Northern Map Turtles at Mount Union, Pennsylvania, between 2000 and 2008 and then individually marked and released 691 hatchling turtles into the Juniata River. During a recent six-year period (from 2017 to 2022), 46 of the hatchling-marked turtles (6.7%) returned to Mount Union as adult females to nest. The ages of these turtles ranged from 11–22 years at first recapture, and their mean age was 17 years. Forty-one hatchling-marked females came from observed nests with known mothers, and remarkably, just four (of 52) mothers produced over half of the returning females. The minimum ages of the oldest female turtles were estimated at 39 years, with reproductive lifetimes of at least 23 years. Our results indicate that a few long-lived Super Moms have made extraordinary contributions to hatchling recruitment and population viability of Northern Map Turtles of the Juniata River. The timing of release also had a significant influence on the probability of a turtle returning, with hatchlings released in May returning at a higher rate than those released earlier in the spring. In addition, morphological characteristics of hatchling-marked females suggest that factors causing shell shape abnormalities in adult turtles have not abated over the past two decades as previously theorized and likely involve exposure of juveniles to contaminants in the Juniata River rather than any maternal influence.