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Summary Ten Barn Owls were tested in a sound-room with recordings of various alarm calls and noise. The owls readily responded with head movements to the majority of stimuli and correctly oriented to their source. The seeet alarm call and the ‘warning’ call elicited the least responses, but they were properly localized by all owls which did respond. This suggests that rather than non-localizability accounting for the fewer observed responses to the seeet and ‘warning’ calls, there is either something else in the quality of those sounds, or in the manner in which they are processed by the bird, which does not elicit responses to the degree that transient sounds with broad frequencies do. Selection in these predators for non-responsiveness is suggested as a counter-strategy to minimize futile energy expenditure in attacking, or otherwise responding to an alerted prey. An additional hypothesis, consistent with Darwin's antithesis principle, is proposed whereby intraspecific and interspecific selection, rather than predator selection for non-localizability, has led to the evolution of seeet and mobbing calls. |
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