Calling Activity of a Stream-Breeding Frog from the Austral Neotropics: Temporal Patterns of Activity and the Role of Environmental Factors

Animal activity patterns can be influenced by selection pressures from local environmental conditions that might fluctuate at different temporal scales. Although studies with frog species and local populations can suggest how variation of environmental factors affects activity patterns, this topic has received little coverage for Neotropical diurnal frogs that inhabit streams, particularly for subtropical species. We described the temporal patterns of calling activity of Schmidt's Spinythumb Frogs (Crossodactylus schmidti) in southern Brazil and investigated the role of environmental factors on this activity. We recorded local environmental variables and monitored calling activity from October 2011 to September 2012, by counting the number of calling males and the number of emitted calls at hourly intervals throughout the day. Male frogs engaged in calling activity year-round, despite the local climatic seasonality. There was no seasonality in the number of calling males or in the number of calls; moreover, variation in photoperiod did not affect the duration of the calling activity throughout the year. Crossodactylus schmidti showed a predominantly diurnal calling activity, with a spike in the early morning followed by a gradual increase in activity during daytime hours, and a subsequent decrease in activity at dusk. Environmental factors had varying effects on calling activity: (1) monthly activity was positively associated with accumulated rainfall and air temperature; (2) early morning activity was greater when air temperatures were higher; and, (3) daytime calling activity was positively associated with light intensity. Whereas our results do not preclude the effect of other environmental factors in the calling behavior of male C. schmidti, accumulated rainfall, air temperature, and light intensity appear to be abiotic regulators of this activity at the analyzed temporal scales. We discuss the biological implications of these environmental factors in the calling activity and reproduction of C. schmidti, and compare the observed patterns with those of other taxa of diurnal stream-breeding frogs.