THE BREEDING BEHAVIOUR OF THE RED‐FOOTED BOOBY SULA SULA
Authors: NELSON J. B. 
Published: April 2008

The breeding behaviour of the Red‐footed Booby on Tower Island, Galapagos, is described. A connection is traced between the arboreal nesting habit and the type and degree of ritualised behaviour; in general territories are large, movement relatively restricted, and territorial and intra ‐pair displays relatively few and undifferentiated when compared, for example, with the North Atlantic Gannet, in which the opposite conditions (dense nesting and maximal inter‐ and intra‐pair contacts) occur.

On Tower Island, 96% of the Red‐footed Boobies are either brown or partly brown forms and 4% are full white forms. The adaptive significance of the polymorphism is discussed, and it is tentatively suggested that the brown form may be more nocturnal than the white.

The average nest density was 0–009 pairs and the maximum density 0'053 pairs per square yard.

Behaviour is considered under the headings: non‐display behaviour (sunning, sleeping, etc.); behaviour with some signal value (Feather Ruffing, Wing Flicking, etc.); behaviour concerned with site establishment (fighting, agonistic displays); pair relationship (mutual displays); incubation and parental care and behaviour of the chick.

Before flying from their territory Red‐foots Wing Flick, a signal action which they have developed to a greater extent than other sulids. Other ritualised wing movements are rarer, possibly because they are associated largely with locomotion preceding flight, which is impracticable for the arboreal Red‐foot.

Sideways Headshaking, a frequent dirt‐dispelling movement in the Gannet, is much reduced in the Red‐foot. Correspondingly, it is much less used in Red‐foot displays, whereas the Gannet incorporates it into many.

Territorial fighting is relatively rare. Territorial behaviour includes Flight Circuiting over the breeding area, Wing Flailing, Jabbing, non‐ritualised Menacing and Forward Head Waving (a ritualised, aggressive, site‐ownership display).

Appeasement displays are poorly developed, being confined in the adult to a fleeting Facing‐away movement. The chick lacks Beak‐hiding and the implication of this for the derivation of allied adult postures is discussed.

Sky‐pointing or Advertising is used by the male to attract a female (occasionally vice versa); it is also a mutual display cementing the pair bond and stimulating co‐operation in coition and nest building. This unusually wide range of functions, compared with other sulids, is perhaps necessitated by this species' lack of a ritualised meeting ceremony. There is little interaction between mates and their aggressiveness to each other remains overt. A noticeable sign of fear on meeting is a marked tremoring of head and neck.

One to three weeks elapsed between starting the nest and laying the egg. Nest‐building movements occur commonly as conflict behaviour during sexual and agonistic encounters. Incubation (tints are lengthy (male average 58‐4, female 60‐7 hours, maximum 199) over the 46‐day incubation period; nest relief is without ceremony.

Feeding of the young, by incomplete regurgitation, averages slightly less than once per day after the young are more than a month old. Young beg distinctively and frenziedly. Parents do not at first discriminate between their own and other young, but do so vigorously when their young can fly. Similarly, young Red‐foots only become hostile to other young when both are well grown and capable of intruding and stealing feeds.

Flight is attained gradually by progressive wing exercising and local sallies. Free‐flying young return regularly (usually daily) to the nest and are fed. Later they congregate in “clubs” and show most of the adult patterns of agonistic behaviour.

The post‐fledging care of the young shown by the Red‐foot (and other boobies) is contrasted with the lack of it in the Gannet, and a hypothesis is suggested for this important divergence within the Sulidae.