Timing of large movement events of pond-breeding amphibians in Western Massachusetts, USA

Understanding the factors influencing the timing of large movement events in pond-breeding amphibians has important conservation implications, especially with regard to establishing road closures aimed at minimizing road mortality. We examined the timing of juvenile emigration and adult immigration in four species of pond-breeding amphibians (Ambystoma maculatum, Ambystoma opacum, Notophthalmus viridescens, and Rana sylvatica) at 14 seasonal ponds in western Massachusetts from 1999 to 2003. Regression trees were variously successful in producing an effective and parsimonious description and robust prediction of large movement events based on a suite of temporal and meteorological variables. Julian date, degree-days, temperature, precipitation and droughtiness were all important correlates of movement for one or more species and age class. The amount of rainfall during the previous 24 h period was an important variable in four of the five trees built, and degree-days was an important variable in two of the three trees built describing juvenile emigration. In four of six cases, regression trees identified a few days each year that accounted for a large percentage of the total annual movement, and thus offered a practical means to determine when road-closure events designed to minimize road mortality of pond-breeding amphibians during migratory events would be most effectively employed.