Monitoring starvation risk: adjustments of body reserves in greenfinches (Carduelis Chloris L.) during periods of unpredictable foraging success

Abstract

Foragers can put on fat as an energy reserve to reduce the risk of starvation. Reserves are necessary to survive periods when energy intake is impossible, and additional reserves can serve as a buffer against periods of little success when foraging is unpredictable; however, maintaining the maximum possible body reserves may be detrimental when measured against a cost of carrying fat. Experiments with greenfinches (Carduelis Chloris L) showed that the birds maintained reserves below the level permitted by food availability. Greenfinches reduced body reserves when exposed to lower metabolic requirements and predictable foraging success; reserves were increased when ambient temperature was lowered or foraging success was made more unpredictable. The response to unpredictability was statedependent. Fatter birds increased their reserves less. The adjustments of energy reserves according to requirements and environmental predictability suggest that it is costly to carry fat and that this cost is balanced against the benefits of carrying body reserves as an insurance against starvation.