Group mobbing behaviour and nest defence in a cooperatively breeding Australian bird

Ke. Arnold, Group mobbing behaviour and nest defence in a cooperatively breeding Australian bird, ETHOLOGY, 106(5), 2000, pp. 385-393
Citations number
Categorie Soggetti
Animal Sciences","Neurosciences & Behavoir
Journal title
ISSN journal
0179-1613 → ACNP
Year of publication
385 - 393
SICI code
Cooperatively breeding noisy miners (Manor ina melanocephala) are well know n in Australia for their persistent and very vocal group mobbing of heteros pecifics. Here I investigated the nature of this extraordinary behaviour, i n particular its role in nest defence, in a colour banded population of noi sy miners in south-east Queensland, Australia. I focused on two questions. First, did the intensity of mobbing vary according to factors such as the t hreat to the nest, or the 'value' of a clutch? Secondly, what role did grou p mobbing play in the success of a nest? To answer these questions, I exper imentally manipulated the nest defence behaviour by placing one of three st uffed models near active noisy miner nests. The response of noisy miners to intruders was not indiscriminate. However, I found that the number of bird s that mobbed a model did not simply reflect the potential threat posed. Th e response of noisy miners to raptors and other potential nest predators ma y have reflected their rarity as well as the threat posed. The number of mo bbers did not vary with the age or size of a brood. In this study, the fate of nests was independent of the number of mobbers or visitors at nests. Fi nally, up to 80% of mobbers were never seen to make any other type of contr ibution to a nest, and many could not be related to the brood that they wer e 'defending'. Hence, for some noisy miner 'helpers' the benefits that they accrued were probably not wholly dependent on the survival of the broods. I suggest that, in this gregarious species, mobbing behaviour at the nest m ay be a display of social status or individual quality. This hypothesis war rants further investigation.