Studies on the behaviour on the South Ausralian fur seal, Arctocephalus forsteri (Lesson) I. Annual cycle, postures and calls, and adult males during breeding season

Abstract

The behaviour of A. forsteri was studied at the South Neptune Is. in 1969-70. This paper elucidates the annual cycle, describes 20 postures and calls (several for the first time), and discusses the behaviour of adult males during the breeding season. Two factors are essential in a breeding colony: water for cooling on hot days and access routes to higher areas for females and pups during heavy seas. The young were all weaned by one year of age and absent from the island during the breeding season. A rapid increase in numbers of females occurred in early November. Births were recorded from 29 November to 22 January but the peak of pupping occurred about 20-30 December. Mating occurred from early November to late January with a peak at about the beginning of January. Numbers of adult males and females in the breeding colonies decreased sharply by mid-January. The overall ratio of adult males to females was 1 : 6-8. In South Australia some adult male A. forsteri were present on the breeding colony all the year round. Large loosely defined territories were defended in mid- October but permanent territories, for the duration of the breeding season, were not established until the latter half of November. No truly aquatic territories were held. Intertidal reefs and areas without pools of water or access to the sea were held only temporarily. Fighting between adult males was highly ritualized and, although encounters were often intense, serious injuries were rare; 30.9% of 2013 recorded disputes in the breeding colonies were resolved with fighting. In only two of these instances did a third male enter the fray. There were more encounters per hr during the period of territory establishment (November) than during the period of pupping and breeding (mid-December to early January). In 367.16 hr of total documentation of the activity of territorial males it was shown that 91 - 14% of the time was spent either lying (72.32 %) or sitting alert (1 8.81 %). This was contrary to statements in the general literature on polygamous land-breeding seals which inferred that males were constantly active. Males exist on stored energy while defending territories, so that conservation of energy (as demonstrated here) lengthens the period a male can stay ashore and maximizes his reproductive potential. Sixteen males defended territories for a range of 21-54 days with a mean of 36.6 & 9.7 days. Territorial males tried to stop females from leaving their territories but could not do so against their will. No aquatic matings were observed. There was little premating behaviour and the mean duration of 30 complete copulations was 6.56+ 2.19 min. Limited data indicated that males became more efficient with experience. Subordinate males defended temporary territories on the dry rock above the dominant males on permanent sites. During heavy seas the dominant males remained with their territories while the females and pups moved up into the temporary territories. Females appeared non-selective when in oestrus and were mated by the subordinate males during periods of high seas. This results in a much wider range of contribution to the population's gene pool than might be expected from the territorial system.