Vocalizations and Reproductive Behavior of Male Pickerel Frogs, Rana palustris

Abstract

I performed playback trials with and recorded vocalizations of male Pickerel Frogs, Rana palustris, in 1992–1993 and 1998–2000 at sites in Delaware and Pennsylvania. I also conducted a mark-recapture study of one population throughout its 1998 breeding season at the Ashland Nature Center, Delaware. Rana palustris had a prolonged breeding season with chorusing occurring over more than one month on nights that the air temperature was at least 8°C. Individual males during the breeding season participated in most choruses, were faithful to specific calling sites, and lost body mass. In the playback trials, I recorded male vocalizations during control conditions and after the playback of one conspecific advertisement call. Males had a complex vocal repertoire consisting of at least three call types: an advertisement call and two additional calls (“snicker” and “growl”) that were elicited by the playback stimulus or exchanged during natural male-male interactions. The three call types had distinct combinations of duration and pulse rate, and the snicker and growl had similar dominant frequencies that were significantly lower than those of the advertisement call. All males in the playback trials eventually returned to advertisement calling; however, these calls differed from the calls emitted during the control period in that they had shorter durations, longer rise times, and a shift of energy toward lower frequencies. Several males responded to the stimulus by emitting a series of underwater calls before returning to the water's surface and calling into the air. Overall, R. palustris has a complex communication system in terms of number of call types, the ability to alter call properties, and the ability to vocalize in both air and underwater.