Little evidence for visual monitoring of vigilance in zebra finches

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Abstract
Several models of vigilance assume that it can be adjusted in response to levels maintained by companions. However, the assumption of visual monitoring of vigilance has received little empirical scrutiny. Various treatments in a laboratory study manipulated the ability of zebra finches (Taenopygia guttata) foraging in pairs to monitor visually the vigilance of companions. In one treatment, the insertion of an uncovered partition allowed members of a pair to monitor, if needed, the vigilance of their companion. The addition of a partial cover to the partition in a further treatment eliminated any visual monitoring of vigilance by companions on either side of the partition while leaving the view from the rest of the cage unaltered. The final treatment, without a partition, allowed the feeding behaviour of unrestricted birds to be examined. As birds spent most of their time feeding or vigilant, feeding rate was considered a proxy for vigilance. After an initial difference in feeding rate across treatments, related perhaps to the novelty associated with the insertion of a partition, birds obtained food at a similar rate whether visual monitoring of vigilance was possible or not and whether individuals were physically separated or not. In agreement with recent empirical and theoretical findings, the study provides little evidence for visual monitoring of vigilance in birds.