Social Sounds: Vocal Learning and Development of Mammal and Bird Calls

First, we hear a rustle in the shrubs, and then a bird whose call sounds like “where are you?” From a short distance away, another bird gives a slightly different call: “oh, where are you?” For simplicity, we will call these WAY calls. In answer, several small gray and white wrens fly toward the first caller, giving WAY calls that sound virtually identical to the first caller’s. At the same time, a small flock flies toward the second caller, giving their own WAY calls. A skirmish follows, with much calling on either side. Careful listening picks up distinct WAY calls throughout and another staccato call, which turns out to be a duet. When the dust settles, the small flocks move off in different directions, territory boundaries apparently stable for the day. The birds are stripe-backed wrens, and this species lives in stable groups composed of a dominant pair and their offspring, who cooperate to care for the pair’s brood (Rabenold 1984). Group mates also cooperate to defend their joint territory. The dominant pair advertises boundaries by singing duets, but when a neighbor intrudes, WAY calls provide a means of identifying group mates. All males in a group share a repertoire of about 12 WAY calls that they use both to maintain contact among the group and to identify themselves in territory disputes. Female group members have their own shared repertoire of WAY calls (Price 1998a).WAY calls indicate group membership—a kind of badge to indicate “I belong to this group.” All stripe-backed wrens live in social groups, so belonging to a group is critical. But, how do group members come to share calls? Most group mates are closely related, so call similarity based on genetic similarity is one possibility. Yet, calls are passed down along sex-specific lines, and a genetic mechanism for this is difficult to envision. Instead, it seems that calls are learned—sons copy their fathers and daughters copy their mothers, and do so with remarkable precision. Like a surname passed on from father to son, or mother to daughter (Price 1998a), calls convey family identity (Price 1999). The patterns observed suggest that call sharing is essential to call function. Although most males in a group are closely related, occasionally