Nest Site Selection in the Terrapin Malaclemys terrapin

Abstract

Northern diamondback terrapins nesting in sand dunes on Little Beach Island, Brigantine, New Jersey were studied during June and July 1973 to determine the factors affecting the timing of egg laying and the selection of nest sites. One to three censuses were taken daily over a transect 800 m long and 18 m wide at various times of the day. Turtles were found laying from 10 June through 23 July, between the daylight hours of 0700 h to 1900 h. There was no correlation between the time of day and the number of turtles on the nesting area. There was, however, a high positive correlation between the number of turtles in the census area and the height of the tide. Beaching at high tide decreases the time the turtle is exposed to predation, thermal stress and desiccation, decreases the distance the turtle must walk to reach the nesting area, and increases the turtle's chance of nesting above high tide. The nesting area of diamondback terrapins is an old, vegetated dune near a cove and behind the barrier beach. Within the study area the turtles preferred to nest in the high dune area compared to available low dune and flat sand areas. However, specific nest sites were on low slopes in areas of low vegetation cover. Nesting in a vegetated area provides a stable substrate, while placing the nest away from the vegetation reduces the number of roots encountered while digging. We suggest that the choice of high dune areas functions to promote laying well above the high tide. Nesting on low slopes within the high dune area minimizes the problems of digging on a steep incline and reduces erosion around