THE BREEDING BEHAVIOUR OF THE WHITE BOOBY SULA DACTYLATRA*
Authors: Nelson J. B. 
Published: April 2008

The aim of this paper is to describe the form and interpret the motivation, function and derivation of breeding behaviour in the White Booby. Attention is paid to adaptive aspects and an effort made to correlate behaviour with environment? particularly colony density and associated degree of competitive behaviour. The absence, simplicity or complexity of certain displays can be correlated with the extent to which highly developed social and /or pair interaction are needed.

Throughout I have tried to place White Booby behaviour in the framework of behaviour in the Sulidae as a group and particularly to compare it with Gannet behaviour, since the latter nest more densely than other sulids and show more extreme aggression and greater ritualization of behaviour patterns used in interpair and wider social communications. The White Booby provides an interesting contrast.

After a brief account of morphology and voice the points are made that White Booby colonies are generally smaller and much less dense than those of the Gannet or Peruvian Booby and also that White Boobies breed in a wide variety of habitats. Site establishment, pair formation, later pair relations, social interactions, body maintenance behaviour, incubation and care of young are described and an account of behaviour in the young is given.

The male establishes the site and shows yes /no headshaking as an aggressive, site‐ownership display, often performed after landing. He attracts the female with a sky‐pointing display which is homologous with sky‐pointing in the Gannet, where, however, it subserves a different and, it is argued, phylogenetically older function, signalling that a bird is about to leave the site rather than serving as an advertizing display. In the White Booby it is thus a good example of a motivationally and functionally emancipated display.

When the pair meet, mutual jabbing, a hostile‐looking and relatively undifferentiated meeting ceremony, and bill‐touching occur. Symbolic nest building plays an important part in White Booby pair behaviour, though the nest is structurally negligible. Nest building is associated with copulation, in which the female is not gripped. Bill‐up‐face‐away is a bill‐averting posture used when a booby moves away from its mate. It is probably an appeasement posture and, so far as the situation “I am about to move” is concerned, seems to have taken the place of Gannet sky‐pointing, the latter having become the booby's advertizing. Wing rattle is a movement probably partly functional in preparing feathers for flight, but is also used as signal behaviour prior to take‐off, particularly during the frequent flights around the breeding area that White Boobies show early in the season. Wing flapping, sometimes with rotary headshaking, is mainly feather maintenance behaviour. The forms of headshaking and head flinging are described. Reciprocal allo‐preening occurs; it is suggested that it can do so without disadvantage since White Boobies possess mutual jabbing—an interaction which can accommodate any aggression engendered by the pair pointing bills at each other, as required for reciprocal allo‐preening.

The average incubation spell in the male is 30 hours and in the female 25 hours; all sulid males show this tendency to spend longer on the site. Seasonally, too, there is a marked sex‐difference in site attendance and this is depicted in graphs for different categories of White Boobies.

The young are left unguarded from about four weeks of age and move off the site. They are fed about 1.4 times per day. They respond to adult investigation or attack by beak‐hiding—an effective appeasement posture. Soon, they perform aggressive territorial behaviour and dispel other young and adults. They return to the site to be fed for around 50 to 60 days after they become free‐flying and show all forms of territorial behaviour.

The discussion is mainly concerned with the correlation between nesting density, aggression and associated appeasement behaviour. It is concluded that, overall, the White Booby's ritualized postures and displays are less well differentiated than those of the Gannet, though individual behaviour patterns may be more complex. The pair relationship in the White Booby approximates more closely to that normally found in birds, where the male is not outstandingly aggressive to his mate.