Can starlings use a reliable cue of future food deprivation to adaptively modify foraging and fat reserves?

Abstract

Regulation of mass in small birds is based on simultaneously minimizing starvation and predation risk, but the mechanisms birds use to assess starvation risk are still debated. While we know that birds anticipate periods of unpredictable food availability/energy expenditure (e.g. the winter and night) by increasing their fat reserves, we do not know whether this anticipation involves learning. This study investigated whether birds could learn to use a light cue that predicted a period of food unavailability, to adaptively regulate their foraging and/or body weight. Sixteen captive starlings, Sturnus vulgaris, were subjected to 42 days of an irregular schedule of food deprivation that involved depriving them of food for 5 h on 20 pseudorandomly chosen days. Birds were randomly allocated to two treatment groups for which a 30 min period of reduced ambient light either provided perfect information (Predictable) or no information (Unpredictable) about upcoming food deprivation. Both groups of birds increased their dawn body mass over the period of the experiment, consistent with a response to unpredictable food deprivation. However, no differences in either foraging behaviour or dawn body mass emerged between the groups, suggesting that the Predictable birds were unable to learn to use the light cue to initiate anticipatory foraging ahead of food deprivation. Furthermore, both groups immediately decreased their foraging behaviour in response to the onset of the light cue, suggesting that starlings do not have an evolved anticipatory foraging response to low light levels. Further work is needed to test alternative cues and designs before any general conclusions can be drawn regarding the flexibility of anticipatory foraging.