Emigration Timing of Juvenile Pond-Breeding Amphibians in Western Massachusetts

—Understanding the timing of movement events of pond-breeding amphibians to and from breeding and natal ponds, respectively, is essential to implementing effective conservation and monitoring strategies for this group of vertebrates. In this study, we assessed the emigration timing of newly metamorphosed juveniles of four species of pond-breeding amphibians (Ambystoma maculatum, Ambystoma opacum, Notophthalmus viridescens, and Rana sylvatica) in western Massachusetts from data collected at 14 seasonal ponds during four consecutive years (2000–2003). Results identified emigration ‘‘windows’’ for juveniles of each species during each year and for all years pooled. Additionally, analyses identified considerable intraspecific variation in the timing of emigration among ponds and years for at least three of the four study species. Our results are directly applicable to management strategies (e.g., roadclosures) aimed at minimizing human-related impacts (e.g., road mortality) on populations of pond-breeding amphibians, as well as to mitigation strategies (e.g., maintaining engineered wetlands with an appropriate hydroperiod length) employed in cases of direct habitat loss. The timing of emigration away from natal ponds by newly-metamorphosed pond-breeding amphibians has received surprisingly limited attention in the scientific literature (but see Shoop, 1974; Paton et al., 2000; Paton and Crouch, 2002). The majority of quantitative studies to date have been conducted at limited spatial (single pond) and temporal (single year) scales (e.g., Loredo and Van Vuren, 1996; Paton et al., 2000). Given the often dramatic biophysical differences among ponds, even those in close proximity (e.g., Jackson and Griffin, 1991), and the pronounced annual variability in conditions likely affecting juvenile emigration (e.g., air temperature, precipitation), studies examining the phenology of emigration must be conducted at adequate spatial and temporal scales (i.e., multiple ponds and years) before robust inferences can be made. Understanding the timing of juvenile emigration has important conservation and management implications. For example, the implementation of road closures during nights of mass amphibian movements is gaining popularity as a conservation strategy, especially in response to recent evidence suggesting road mortality can have a significant, negative impact on local population persistence (Gibbs and Shriver, 2005). Currently, however, road closures are typically only employed during adult migration periods (P. W. C. Paton, pers. comm.). Extending road closures to include mass juvenile emigration events requires a better understanding of juvenile emigration. With regard to land management, understanding the timing of juvenile emigration is prerequisite to the design of effective mitigation wetlands. In particular, engineering seasonal ponds with appropriate hydroperiods for larval development to metamorphosis and emergence of target species requires an understanding of juvenile emigration timing at natural wetlands (Rowe and Dunson, 1995; Snodgrass et al., 2000; Paton and Crouch, 2002). A better understanding of emigration timing of juveniles may also help to explain year-to-year variability in larval success, especially when paired with hydrology data (e.g., in years when rainfall levels are low, ponds may dry up relatively early, and species that typically do not complete metamorphosis until later in the year may experience partial or complete reproductive failure; Pechmann et al., 1989). This may be particularly relevant given some climate change models, which predict that weather patterns may exhibit much greater variability than has occurred in recent history (Houghton et al., 2001; Hulme et al., 2002). Our study examines emigration timing of newly metamorphosed individuals of four species of pond-breeding amphibians (Spotted Salamander, Ambystoma maculatum; Marbled Salamander, Ambystoma opacum; Red-Spotted Newt, Notophthalmus viridescens viridescens; and Wood Frog, Rana sylvatica) at 14 seasonal ponds between 2000 and 2003 in western Massachusetts. The objectives of this study were to (1) evaluate the timing of juvenile emigration from natal ponds, and (2) compare the timing of emigration across ponds, years and species. 1 Corresponding Author. E-mail: timm@forwild. umass.edu Journal of Herpetology, Vol. 41, No. 2, pp. 243–250, 2007 Copyright 2007 Society for the Study of Amphibians and Reptiles