• DOI:10.1016/S0003-3472(05)80566-4
• Corpus ID: 53170079

The social structure of Arabian babbler, Turdoides squamiceps, roosts

@article{Bishop1991TheSS,
  title={The social structure of Arabian babbler, Turdoides squamiceps, roosts},
  author={R. P. Bishop and A. Groves},
  journal={Animal Behaviour},
  year={1991},
  volume={42},
  pages={323-325}
}

• R. P. Bishop, A. Groves
• Published 1 August 1991
• Biology
• Animal Behaviour

Arabian babblers are cooperatively breeding birds living in groups, whose members defend group territories (Zahavi 1974). Babblers in a particular group typically roost huddled together in a linear array along the branch of a tree, usually Acacia tortillis or Zizyphus spinoeristae. Previous observations had determined that older male birds tend to occur on the outside of roosts (Zahavi 1990). In the present study, we investigated this phenomenon in more detail. The study was carried out between January and April 1984 at Hazeva in the Rift Valley (Arava) Israel, an area in which, since 1971, a colour-ringed population of Arabian babblers has been continuously studied by A. Zahavi. The age and sex of end-roosting birds was determined for the linear roosts of nine colour-ringed groups of babblers by reading the colour rings after dark with the aid of a spotlight. The data are presented in Table I. In all 90 observations the oldest male was observed on one end of the roost. In groups 1-7 the end of the roost not occupied by the oldest male was occupied by either the second, third or, on one occasion, the fourth oldest male, with the second oldest male occupying this position most frequently. Females were not found on the ends of roosting arrays except in groups 8 and 9 in which the oldest female occupied the opposite end to the oldest male. Groups 8 and 9 differed from the others in that group 8 contained only one male (and therefore a female was necessarily on one end of the roost) while group 9 contained only offspring of the oldest male and female, the three male offspring all being at least 7 years younger than the oldest female. These data demonstrate that among Arabian babblers the oldest male birds tend to occupy the outside positions in night roosts in contrast to the situation observed in the night roosts of rooks, Corvus J?ugilegus (Swingland 1977), red-winged blackbirds, Agelaius phoeniceus (Weatherhead & Hoysak 1984) and starlings, Sturnus vulgaris (Summers et al. 1987) in which older male and, in the case of starlings, heavier birds occupy internal sites in communal roosts while younger and female birds are found on the outside. A similar situation in which older birds roost on the sides and younger birds in the middle was also observed in the Indian jungle babbler, Turdoides striatus, by Gaston (1977). Summers et al. suggested that in starling roosts external positions are more costly in terms of thermoregulation and/or risk of predation and that dominant birds outcompete subordinates for the more favoured internal positions. At the Hazeva study site, end-roosting babblers (one an alpha and one a beta individual) were twice seen to be killed and regurgitated by snakes (Zahavi, personal communication) suggesting that outside roost positions may be susceptible to predation. One possible advantage of roosting in end positions is that this would facilitate more rapid take-off in the event of a predator attack. However, this is not applicable to the Hazeva babblers since all roosts studied were situated in dense thorn trees which precluded rapid take-off from any position. Since older babblers are dominant to younger ones (Zahavi 1988, 1990) it is therefore of interest that the oldest male birds were found to occupy end roost positions. A possible explanation for the tendency for older male birds to be on the end of roost arrays in babblers is that kin selection (Hamilton 1964) is involved and that older male birds are, on average, more highly related to other group members than to other birds. Alternatively, end roosting may be related to social status either because it may reliably 'advertise' individual quality and therefore be involved in the determination of social status (Zahavi 1975, 1977) or because birds of higher social status are better able to bear the costs of end roosting. These explanations are not mutually exclusive and the two effects may be confounded. To examine the possible involvement of kin selection, indices of average relatedness of the three oldest males and the oldest female to other group