Abstract
Flying animals need to accurately detect, identify and track fast-moving objects and these behavioral requirements are likely to strongly select for abilities to resolve visual detail in time. However, evidence of highly elevated temporal acuity relative to non-flying animals has so far been confined to insects while it has been missing in birds. With behavioral experiments on three wild passerine species, blue tits, collared and pied flycatchers, we demonstrate temporal acuities of vision far exceeding predictions based on the sizes and metabolic rates of these birds. This implies a history of strong natural selection on temporal resolution. These birds can resolve alternating light-dark cycles at up to 145 Hz (average: 129, 127 and 137, respectively), which is ca. 50 Hz over the highest frequency shown in any other vertebrate. We argue that rapid vision should confer a selective advantage in many bird species that are ecologically similar to the three species examined in our study. Thus, rapid vision may be a more typical avian trait than the famously sharp vision found in birds of prey.
Highlights
High critical flicker fusion frequency (CFF) has been shown to correlate with high metabolic rate and small body size, predicting that vertebrates with the size and metabolic rate of small passerines should perceive visu
The average CFFs of these species, 130.3 ± 0.94 Hz (±SD) in three blue tits, 128.1 ± 9.8 Hz in seven collared flycatchers and 138.2 ± 6.5 Hz in eight pied flycatchers, are clearly higher than those of humans and around 40 Hz higher than for any other vertebrate tested to date [2, 3]
High CFF has been shown to correlate with high metabolic rate and small body size, predicting that vertebrates with the size and metabolic rate of small passerines should perceive visual
Summary
High CFF has been shown to correlate with high metabolic rate and small body size, predicting that vertebrates with the size and metabolic rate of small passerines should perceive visu. We have performed behavioral experiments to estimate temporal resolution of the complete visual pathway in three species of small passerine birds: blue tit (Cyanistes caeruleus), collared flycatcher (Ficedula albicollis) and pied flycatcher (F. hypoleuca). We used an operant conditioning approach in which the birds were trained and tested for the task of distinguishing flickering from constant stimuli produced by LED-arrays simulating daylight.
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