Environmental factors influencing calling in sympatric anurans.

Anuran reproduction is influenced by various biotic and abiotic factors, of which temperature and rainfall are the best studied. Here we examine the relationship between multiple abiotic environmental variables - specifically, air and water temperature, rainfall, barometric pressure, relative humidity and wind velocity - and the calling activity of five species (Rana sylvatica, Pseudacris crucifer, Bufo americanus, Rana clamitans, and Rana catesbeiana) in an anuran community in New Brunswick, Canada. Acoustical and environmental data were sampled hourly for 4 months during the breeding season in 1997. Logistic regression analyses indicated that each species responded to a unique combination of meteorological variables, even when calling concurrently. Calling in the spring breeding species, R. sylvatica, P. crucifer, and B. americanus, was most associated with the time of day (i.e., they called primarily at night), while calling in the summer breeding species, R. clamitans and R. catesbeiana, was associated primarily with high water temperature. Species with short breeding periods (i.e., explosive breeders; R. sylvatica, B. americanus) responded to fewer environmental variables than did species with prolonged breeding periods (P. crucifer, R. clamitans, R. catesbeiana). Prolonged breeding species responded differently to climatic variables throughout the breeding season: during the latter half of their calling periods, the time of day and a variable that predicts rain, i.e., barometric pressure, became more important, and water temperature became less important.