Who is Calling? Intraspecific Call Variation in the Aromobatid Frog Allobates femoralis

Many territorial species respond less aggressively to familiar neighbours than to unfamiliar floating strangers based on individual differences in acoustic signals. This form of social recognition, termed neighbour-stranger discrimination (NSD) or dear-enemy phenomenon has been reported so far from three anuran species. To investigate the potential of auditory signal features to convey information on sender's identity, we determined patterns of within-male and between-male variability in the advertisement call of the aromobatid frog Allobates femoralis. We examined 285 calls from 19 males to assess those call properties showing sufficient and reliable inter-individual differences to function as possible recognition cues. Beside calls per call bout and call rate, all other examined call properties were more variable among males than within males. Generally, temporal call features showed higher between- and within-male variability ratios than spectral properties and contributed mostly to distinguish individual males in the discriminant-function analysis. Mean classification success of 64.9% correctly assigned calls to individual males is mainly attributable to three temporal call properties (duration of note 1 and 4, note repetition rate). Altogether, our results suggest that there is sufficient variation in the advertisement call to discriminate statistically among individual males. However, assessed call differences between A. femoralis males were rather small, suggesting that potential NSD might be based either on a combination of call features or even on the whole pattern of individual call variation instead on single call properties. Habituation-discrimination experiments in the field using modified playback signals to test for differential behavioural responses are required to confirm this hypothesis.