Rapid effects of corticosterone on cache recovery in mountain chickadees (Parus gambeli).

Environmental perturbations increase adrenal activity in several vertebrates. Increases in corticosterone may serve as a proximate trigger whereby organisms can rapidly adapt their behavior to survive environmental fluctuations. In food-caching songbirds, inclement weather may present the need to alter caching and/or retrieval behaviors to ensure food supplies. We hypothesized that corticosterone may increase the rate of caching and/or retrieval behaviors in the mountain chickadee, a food-storing songbird, and tested if these potential effects were mediated by alterations in appetite, activity, or memory for cache sites. Corticosterone or vehicle was administered to subjects 5 min prior to either caching or recovery in a naturalistic laboratory paradigm during which we recorded the number of caching events, sites visited, and seeds eaten (caching) or caches recovered, total sites visited, cache-related visits, and non-cache-related visits (recovery). Data were analyzed using nested ANOVA for treatment within sequential trial. There was no effect on any caching behaviors following treatment. However, birds treated with corticosterone during retrieval recovered more seeds and tended to visit more cache-related sites than did controls. Since groups did not differ in the number of seeds eaten or the total number of sites visited, it seems unlikely that corticosterone affected appetite or activity. Rapid surges in corticosterone may increase the efficacy of an underlying memory process for cache sites which is reflected in higher cache recovery in corticosterone-treated birds than in controls. Thus, rapid alterations in plasma corticosterone following environmental change may alter memory-reliant behaviors which promote survival in the food-caching mountain chickadee.