Vocal behaviour of the frog Eleutherodactylus antillensison the British Virgin Islands

The vocal repertoire of male Eleutherodactylus and the communicative significance of two calls (trill and courtship call) were investigated under natural conditions on the British Virgin Islands. Interspersed with two-note advertisement calls, males uttered trill calls, which typically consisted of an introductory note followed by five to 13 rapidly repeated notes. The introductory note and the repeated notes were within the range of the dominant frequencies of the first and second note of the advertisement call, respectively, but their mean frequencies were 5-8% higher. The temporal and spectral characteristics of the trill and advertisement calls were similar on three islands (Tortola, Virgin Gorda, Guana), except that the number of repeated notes in the trill was higher on Guana. Body size and air temperature had no detectable effects on the call characteristics. In response to experimental playback of trill calls (either synthesized or constructed from actual calls), males produced more trills in the period following the stimulus than during the baseline. During the playback itself, five or 22 males produced an unusually high number of trills that alternated with the stimulus trills. These responses suggest that the trill is an aggressive call used in the defence of a calling territory. In response to the playback of courtship calls (multi-note calls that males uttered only in the presence of a female and that differed from the trill call mainly in the dominant frequency of the repeated notes), 11 of 28 males left their perch sites and nine approached the speaker. In contrast, males never left their perches during the baseline or the trill stimulus. These responses suggest that males may exploit the courtship calls of rivals to obtain mates through interference.