Helpers Have Little to Laugh About: Group Structure and Vocalization in the Laughing Kookaburra Dacelo novaeguineae

Abstract

Laughing Kookaburras Dacelo novaeguineae combine a conspicuous group vocalisation with a social structure in which subordinate helpers assist a dominant breeding pair in raising young. The structural and temporal characteristics of the laugh song in captivity and in the field were related to spatial distribution of group members, to social interactions within and between groups and to group size and territory size. Under all conditions, group songs lasted longer than pair songs and contained a higher proportion of the loudest element, the actual laugh part. Other parameters of song structure did not differ either with group composition or context. Joint songs fell into two categories: those during the day, (usually involving the breeding pair only); and those at the roost during dusk and dawn, usually involving all group members, i.e. the pair plus one to three helpers. Songs without the breeding pair or with only one member of it were rare. The spatial distribution of group members during singing was almost identical to that when not singing, but differed from a random distribution. Songs at the roost amounted to about 60% of all songs produced and shifted with the times of sunrise and sunset. At dusk, song frequency was mainly determined by group size and at dawn mainly by the total number of neighbours. During daytime, singing was usually connected with inter- and intra-group disputes. We conclude that the Kookaburras's laugh song signals aggression and aids in (a) defending a temtory, (b) guarding the mate and (c) establishing and maintaining a dominance hierarchy between breeders and helpers. In this last context (c) helper singing, especially during daytime, indicates a challenge to a breeder's status.