Search Modes of Birds and Lizards: Evidence for Alternative Movement Patterns

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Abstract
Many studies classify predators as either "sit-and-wait foragers" or "active searchers" and contend that these two search strategies correlate with syndromes of behavioral, physiological, and morphological traits (the syndrome hypothesis). I use move-frequency data (moves per minute) for 58 species of forest birds and 22 species of lizards to study whether the move-frequency distributions of these two predator types are bimodal. A statistical test designed to distinguish bimodal from unimodal distributions indicates bimodal distributions of move frequencies for both taxa. Further, observed cumulative distributions of move frequencies are not significant different from predicated, bimodal distributions. Conversely, normal, lognormal and uniform distributions provide inadequate descriptions of move frequencies. The same conclusions are reached when Australian and North American birds are considered separately. Hence, for birds and lizards, the dichotomous view of predator search stategies is realistic; however, there is variation within the two basic movement patterns. I also compare the move frequencies of Australian birds with their North American counterparts and of birds with lizards. The Australian and North American samples have similar proportions of sit-and-wait foragers and active searchers, and the difference between an average sit-and-wait predator and an average active searcher is similar for both taxa. Birds in the Australian sample, however, move more frequently, on the average, than those in the North American sample. Lizards move less frequently than birds, and a larger proportion of the lizards are sit-and-wait foragers. Although several lines of evidence suggest that the search modes of lizards might be more polarized than those of birds, this hypothesis is rejecetd. The syndrome hypothesis treats sitting and waiting and actively searching as species-specific strategies and contends that physiological and morphological traits constrain a predator''s ability to switch between modes. To guide future examinations of this hypothesis, I (1) demonstrate aht move frequency is a good descriptor of search mode, (2) argue that the approach used in this interspecific analysis can be employed intraspecifically to determine whether predators switch search tactics. (3) suggest that the degree to which physiology and morphology limit a predator''s ability to switch modes can be examined by comparing intraspecific move-frequency distributions against the interspecific distributions provided here, and (4) provide two hypotheses for the bimodality observed in the move-frequency distributions of birds and lizards.