Courtship calls and behavior in two species of chorus frogs, genus Pseudacris (Anura: Hylidae)

We studied the courtship behavior of two species of chorus frogs, Pseudacris illinoensis and P. triseriata, in western Illinois. We report observations of courtship behavior and describe courtship calls for each species. These calls were given in response to both male and female conspecifics entering the calling spaces of resident males. Courtship calls given in response to an intruder were never followed by aggressive behaviors from the resident or the intruder, and courtship calls were never given in response to playbacks of conspecific advertisement calls. Thus, these calls do not appear to be used in an aggressive context. Courtship calls of P. illinoensis are longer in duration than advertisement calls. Courtship calls in P. triseriata consist of multiple notes compared to single note advertisement calls. These courtship calls have higher pulse rates and lower dominant frequencies, and they are given at faster calling rates than advertisement calls. Courtship calls of both species are more variable in structure within males than advertisement calls. Like two other species of chorus frogs for which courtship calls have been reported, courtship calls in P. iffinoensis and P. triseriata are modifications of the advertisement call. Courtship calls in the genus that have been described so far do not appear to share a common structure. The recognition of courtship calls in a chorus may play a useful role in long-term monitoring of anuran breeding activity, especially in remotely determining the presence of gravid females.