Humpback whale songs: Do they organize males during the breeding season?

Male humpback whales (Megaptera novaeangliae) emit an ever-changing series of sounds during the breeding season known as song. The purpose of this study was to describe the behaviour and interactions of singers and, within this context, hypothesize song function. A sample of 167 singer interactions was collected from 1997-2002 off Maui, Hawaii. Singers typically: (1) were lone adults (80%); (2) sang until joined by non-singing males (89%), at least some of which had been neighbouring singers; (3) engaged in brief interactions (80% < 10 minutes); otherwise the pair stayed together until a subsequent interaction; (4) were involved in non-agonistic interactions (80%); and (5) were involved in series of such interactions across the breeding ground (documented in 25% of sample) which could lead to one or more of the interacting males joining a group that included a female (documented in 13% of sample). A singer-joiner interaction proceeded directly to apparent cooperative behaviour around a female in two cases; this relationship was not ruled out in similar interactions. The two key elements of male behaviour during the breeding season are a song that unites males, but changes collectively and a wide range of male relationships that range from agonistic, to non-agonistic, to cooperative. We hypothesize that the song organizes males by providing, through its characteristics of continuous change and adoption of these changes by all nearby singers, a real time measure of association between individuals, possibly providing a means of reciprocity for mutual assistance in mating.