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


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


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.