A Model of Search Behaviour for the Northern Wheatear Oenanthe oenanthe (Aves, Turdidae) and Other Pause-travel Predators

Authors


British Ornithologists' Union and Edward Grey Institute of Field Ornithology, Dept. of Zoology, South Parks Road, Oxford OX1 3PS, England

Abstract

Many animals hunt by pausing to scan a particular locality then moving rapidly to the next pausing position. Prey are spotted from pausing positions. I develop a descriptive and analytical model which relates the distance moved between pauses (move-length) to the area scanned at each pause, and which relates search rate to these two variables, and to pause time and running speed. The northern wheatear uses pause-travel to hunt invertebrates on short grassland. Wheatears used a search pattern which reduced the distance moved to the minimum consistent with avoiding previously-searched ground. The chosen move-length maximized search rate at any given pause duration and running speed. When movement accounted for a small proportion of search time, search rate was little affected by variations in running speed. Incubating females searched faster, with shorter pauses, than males and non-incubating females, but captured prey at a faster rate which implied reduced selectivity. The model showed that wheatears do not exhibit area-restricted search by searching an area more than once, while plovers (Charadriidae) sometimes do, although previous assumptions about the search patterns which lead to area-restricted search need to be modified. Examples from plovers, chats and thrushes (Turdidae) and tyrant-flycatchers (Tyrannidae) show that pause duration is affected by prey visibility and density, and that search radius is affected by prey visibility.

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