Good foragers can also be good at detecting predators

Abstract

The degree to which foraging and vigilance are mutually exclusive is crucial to understanding the management of the predation and starvation risk trade-off in animals. We tested whether wild-caught captive chaffinches that feed at a higher rate do so at the expense of their speed in responding to a model sparrowhawk flying nearby, and whether consistently good foragers will therefore tend to respond more slowly on average. First, we confirmed that the time taken to respond to the approaching predator depended on the rate of scanning: as head-up rate increased so chaffinches responded more quickly. However, against predictions, as peck rate increased so head-up rate increased and mean length of head-up and head-down periods decreased. Head-up rate was probably dependent on peck rate because almost every time a seed was found, a bird raised its head to handle it. Therefore chaffinches with higher peck rates responded more quickly. Individual chaffinches showed consistent durations of both their head-down and head-up periods and, therefore, individuals that were good foragers were also good detectors of predators. In relation to the broad range of species that have a similar foraging mode to chaffinches, our results have two major implications for predation/starvation risk trade-offs: (i) feeding rate can determine vigilance scanning patterns; and (ii) the best foragers can also be the best at detecting predators. We discuss how our results can be explained in mechanistic terms relating to fundamental differences in how the probabilities of detecting food rather than a predator are affected by time. In addition, our results offer a plausible explanation for the widely observed effect that vigilance continues to decline with group size even when there is no further benefit to reducing vigilance.

Predator detection and avoidance by starlings under differing scenarios of predation risk

“…Many social foraging models assume that vigilance and foraging are mutually exclusive behaviors (Pulliam et al, 1982;Scannell et al, 2001;Ward, 1985). This study adds to growing evidence that they are not so (Cresswell et al, 2003;Guillemain et al, 2001;Lima and Bednekoff, 1999). Under our experimental conditions, we hypothesized that short swards would be better than long swards for foraging starlings, firstly because prey would be more readily available and/or secondly because vigilance could occur while feeding (Devereux et al, 2004;Fernández-Juricic et al, 2005).…”

“…This allowed us to measure relative differences in behavior within individuals that we can attribute to changes in risk across our conditions. Seminatural experiments with enclosures are an accepted method in behavioral ecology to assess the foraging and vigilance responses of test subjects to manipulations (Butler et al, 2005;Cresswell et al, 2003;Powell, 1974;Tinbergen, 1981) because the behavior of animals is generally similar to that exhibited in natural situations (Fernández-Juricic et al, 2005;Olsson et al, 2002;Whitehead et al, 1995).…”

Visual perception and social foraging in birds

“…Some granivorous birds, for instance, appear not to monitor the level of vigilance of flock mates [25][26][27]. These species might benefit only from dilution effects or might not need to monitor the vigilant behaviour of conspecifics because of the large extent of their own visual fields to detect predators through personal detection [28] or through the escape behaviour of conspecifics [25,29,30]. Other birds do show conspicuous conspecific scanning in specific foraging situations [31,32].…”

Are fast explorers slow reactors? Linking personality type and anti-predator behaviour

“…via more frequent and/or longer vigilance bouts) being faster to detect an approaching predator (Cresswell et al 2003). Individuals can vary their vigilance level by allocating their brain's 'attention' between searching for and handling food items and searching for predators (Godin & Smith 1988;Clark & Dukas 2003;Fernandez-Juricic et al 2004).…”