Meeting Abstract
Food supplementation to wild birds occurs across landscapes and over every season. However, natural food abundances may sometimes not be adequate. In winter, especially, natural food availability might be unpredictable whereas the availability of human provided food remains more constant. This variability in resources might then have a negative impact on immune function, as might occur if adequate energy and nutrients for mounting an immune response is not acquired. To test this idea we compared immune function and physiology of captive black-capped chickadees (Poecile atricapillus) with a constant and unpredictable food supply. Control birds received ad libutum food each day of the experiment; birds assigned to the unpredictable treatment received only 80% of their daily energy requirements on random days and ad libitum food on other days. Throughout the course of the study we examined multiple aspects of the immune system (constitutive and induced), body mass, fat and lean mass. Treatment birds maintained higher mass over the course of the study and had significantly higher fat mass compared to control birds. Treatment birds mounted a weaker immune response to lipopolysaccharide; however, they maintained a high level of complement lysis activity compared with control birds. Results from this study demonstrate that during times of variable and uncertain food availability, like extreme weather events or long winters, certain aspects of the immune system might be compromised even if animals maintain more body fat as a hedge against uncertainty.
