Female begging in European robins: Do neighbors eavesdrop for extrapair copulations?

Female European robins beg for food from their mates throughout the breeding season using far-carrying "seep" calls which resemble the begging calls of fledglings. We investigated the possibility that these calls are eavesdropped by neighboring males and used as cues to target intrusions during the fertile period. Female seep calling and male courtship feeding peaked in the fertile period, and males appeared to modify provisioning rate in relation to seep calling rate. Further, there was a positive correlation between rate of courtship feeding and clutch size, both of which tended to be inversely related to seep calling rates. These observations imply that the seep call is a hunger signal directed at pair males. As the signal is loud and given most frequently during the fertile period, it must also contain information about fertility and location. Playback experiments suggested that this information is eavesdropped by neighboring males, who responded to rapid rates of seep calling more readily than slow rates and to calls broadcast at the edge of territories rather than their center, presumably in search of extrapair copulations. Pair males can reduce the intensity of the female's signal by courtship feeding, and thus male provisioning may protect paternity.