Daily foraging patterns in free-living birds: exploring the predation-starvation trade-off - PubMed (original) (raw)

Daily foraging patterns in free-living birds: exploring the predation-starvation trade-off

David N Bonter et al. Proc Biol Sci. 2013.

Abstract

Daily patterns in the foraging behaviour of birds are assumed to balance the counteracting risks of predation and starvation. Predation risks are a function of the influence of weight on flight performance and foraging behaviours that may expose individuals to predators. Although recent research sheds light on daily patterns in weight gain, little data exist on daily foraging routines in free-living birds. In order to test the predictions of various hypotheses about daily patterns of foraging, we quantified the activity of four species of passerines in winter using radio-frequency identification receivers built into supplemental feeding stations. From records of 472,368 feeder visits by tagged birds, we found that birds generally started to feed before sunrise and continued to forage at a steady to increasing rate throughout the day. Foraging in most species terminated well before sunset, suggesting their required level of energy reserves was being reached before the end of the day. These results support the risk-spreading theorem over a long-standing hypothesis predicting bimodality in foraging behaviour purportedly driven by a trade-off between the risks of starvation and predation. Given the increased energetic demands experienced by birds during colder weather, our results suggest that birds' perceptions of risk are biased towards starvation avoidance in winter.

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Figures

Figure 1.

Figure 1.

Theoretical depiction of the bimodal relationship between foraging intensity and time of day.

Figure 2.

Figure 2.

Predicted mean hourly feeder visitation rates per individual based on a generalized linear mixed model (GLMM). Feeding activity generally increased throughout the day, with a sharp decline in activity as sunset approached for three of four species. Results for (a) black-capped chickadee, (b) tufted titmouse, (c) white-breasted nuthatch and (d) house finch.

Figure 3.

Figure 3.

Predicted mean daily feeder visitation rates per individual as a function of average daily temperature (°C) based on the GAMM models. Three of four species visited feeders more often on colder days. Model results for (a) black-capped chickadee, (b) tufted titmouse, (c) white-breasted nuthatch and (d) house finch. The shaded regions represent 95% CIs.

References

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