Back to the basics of antipredatory vigilance: can nonvigilant animals detest attack?

Citation
Sl. Lima et Pa. Bednekoff, Back to the basics of antipredatory vigilance: can nonvigilant animals detest attack?, ANIM BEHAV, 58, 1999, pp. 537-543
Citations number
49
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Animal Sciences","Neurosciences & Behavoir
Journal title
ANIMAL BEHAVIOUR
ISSN journal
0003-3472 → ACNP
Volume
58
Year of publication
1999
Part
3
Pages
537 - 543
Database
ISI
SICI code
0003-3472(199909)58:<537:BTTBOA>2.0.ZU;2-9
Abstract
Many birds and mammals respond to a heightened risk of predation, especiall y that associated with smaller group sizes, with an increase in vigilance. All interpretations of the way in which vigilance responds to changes in pr edation risk assume that animals feeding with their heads down (i.e. animal s in a nonvigilant state) cannot detect approaching predators. We provide t he first explicit test of this assumption by 'flying' a mounted hawk down a 15-m chute towards actively feeding, free-living, dark-eyed juncos, Junco hyemalis. Juncos were targeted individually for simulated attack when they had either a 'head-down' view up the chute, or a completely unobstructed vi ew; a junco with a head-down view could see up the chute only when it lower ed its head to feed. Juncos with an unobstructed view almost always detecte d the hawk;at the maximum distance of 15 m. Juncos with a head-down view us ually detected the attack at a distance of 10-15 m against a grey backgroun d, but detection distances were shorter when attacks occurred against a cam ouflaged background. The results demonstrate that these birds have a consid erable ability to detect approaching predators even when not overtly vigila nt, although their detection ability is greater when they raise their heads . Vigilance sequences, therefore, probably consist of bouts of low-quality detection (active feeding) interspersed with bouts of higher-quality detect ion (overt vigilance) that can only be accomplished at the expense of feedi ng. This realization has major implications for current interpretations of the vigilance group size effect and antipredator vigilance in general. (C) 1999 The Association for the Study of Animal Behaviour.