Effects of Stochastic Flood Disturbance on Adult Wood Turtles, Glyptemys insculpta, in Massachusetts

Résumé

The homing ability of non-marine turtles has been studied in a variety of taxa, and many species appear to be capable of short-range homing on the scale of several hundred meters or a few kilometers following experimental displacement. However, the behavioral response of turtles following a naturally caused displacement has seldom been reported. In this paper, we describe the effect of displacement ranging from 1.4 to 16.8 km (average = 4.8 km) by severe floods in a stream system in Massachusetts. We radio-tracked 38 adult Wood Turtles (Glyptemys insculpta) at five separate sites in Franklin County, Massachusetts, for periods ranging from one to four activity seasons and documented the displacement of a total of 12 Wood Turtles during seven floods between 2004 and 2008. Based on the average rate of displacement per flood and annual flood frequency, we estimate that, during our study, floods displaced over 40% of this Wood Turtle subpopulation annually. We present evidence that displacement results in elevated mortality rates and that displaced Wood Turtles mate and nest in the year following displacement at rates well below average; on a longer time scale, however, displacement by flooding may be an important mechanism of population connectivity in some areas. We also present evidence that most Wood Turtles avoid stream segments with stream gradient steeper than 1%; this may in part reflect an adaptation to avoid severe floods. Regional models and empirical data from stream gages suggest that flood intensity may currently be on an increasing trend. Conversion of upland from forest and fields to impervious surfaces and hardening of upstream riverbanks may have exacerbated recent flooding and decreased the resiliency of the riparian system to increased precipitation.