Evidence for multicontest eavesdropping in chickadees

Abstract

Animals eavesdrop on dyadic interactions between other individuals to gather information for future mate choice and territory defense decisions. The capacity for eavesdroppers to combine information gathered from overhearing multiple two-way interactions is poorly studied. We tested whether inexperienced (second year) and older (after second year) male black-capped chickadees (Poecile atricapillus) eavesdrop on rivals' song contests to evaluate the relative threat levels of multiple unfamiliar territorial intruders. We used a multiple speaker playback experiment to simulate 3 male territorial intruders (A, B, and C) engaging in 2 successive dyadic song contests, presenting focal males with the information that A was more threatening than B, and B was more threatening than C. We then assayed the response of focal males when presented with simulated intruders A and C without relative information. We predicted that males would defend against the intruder perceived to be the greater threat. Focal males initially responded toward the more threatening intruder (A) significantly more than the less threatening intruder (C), consistent with our predictions. Older birds approached the more threatening intruder (A) significantly more than the less threatening intruder (C), whereas young males showed more variable responses. Our results suggest that male chickadees were able to acquire relative threat information from separate song contests that influenced their responses toward rivals paired in novel contests. These findings indicate that territorial songbirds in communication networks may be capable of integrating information gathered through eavesdropping on multiple interactions.