The social organization and vocal behaviour of the saddleback, Philesturnus carunculatus rufusater (Aves).

Abstract

The North Island saddleback (Philesturnus carunculatus rufusater. Family Callaeatidae) is a medium sized passerine bird with wings and pectoral muscles reduced to the point where they cannot support level flight for more than a few metres. Its habitat is dense evergreen forest on a few small islands near Auckland. Formerly abundant this sub-species became extinct about 1900 except for a population which survived on Hen Island. Since 1964 Wildlife Service has successfully recolonised four other islands, including Cuvier Island, where the bulk of this study was carried out. The birds were trapped and colour-banded for individual recognition and field observations were made on their subsequent survival, general biology, social organisation and vocal behaviour. Survival of adult territorial birds is high, reproductive rate is low and it is likely that pairs do not breed in their first year. Survival of fledglings to breeding age is low. The pair-bond normally lasts for life and is fully maintained throughout the year, but the members of each pair separate every evening to roost singly in holes. The pairs also hold permanent territories which are maintained throughout the year by a form of sequestrative behaviour in which mutual avoidance plays an important part. Avoidance behaviour is mediated by loud songs and there is a marked lack of physical aggression. Directed, and undirected song, in the form of counter-singing occurs throughout the year and matched song counter-singing is common. Each male as well as singing the undifferentiated Chatter Songs, also sings from 1 to 4- Male Rhythmical Songs and micro-dialects of these developed around the few birds that founded the Cuvier population. Songs in a dialect were uniform but markedly different between dialects. Recruitment of young birds to the dialects was studied by tracing the song behaviour of colour-banded sons of colour banded fathers whose songs were already known. The songs (M.R.S.) of newly settled birds are derived exclusively by cultural transmission from their neighbours, a process monitored by direct observation in the field. When adult males shifted their songs became modified to match their new song environment. When a new bird developed a variant song sometimes old residents modified their songs to match, but more usually the spread of a variant form occurred through imitation by further young settlers. The origin and development of new dialects have been traced by observing characteristic errors of song learning. A partly hypothetical and partly substantiated scheme of derivation of the M.R.S, patterns and the pathways of their cultural evolution are discussed.