SEASONAL-CHANGES OF THE ADRENOCORTICAL RESPONSES TO STRESS IN REDPOLLS, ACANTHIS-FLAMMEA, IN ALASKA

Male and female redpolls (Acanthis flammea) showed marked increases in circulating corticosterone up to 1 hour after exposure to a common st ress-capture, handling and restraint-indicating that their hypothalamo -pituitary-adrenal axis responded to acute stress in a manner similar to that of other vertebrates. We used this protocol as a measure of re sponsiveness of the adrenocortical cells to acute stress in general an d for comparison with gender and across seasons. In both sexes the adr enocortical response to stress was reduced in January (at Fairbanks, 6 4 degrees N) and maximal when birds were breeding in June at Toolik La ke (69 degrees N). The elevation of circulating corticosterone followi ng capture and handling in breeding males at Barrow (71 degrees N) was significantly less than in breeding males at Toolik Lake. There were also considerable variations among individuals in the intensity of the adrenocortical responses, particularly in the maximum levels of corti costerone attained. This individual variation correlated significantly with fat score and/or body mass in both sexes only in breeding birds at Barrow. This difference may be explained by generally lower, and th us reduced variability in body fat and mass in birds sampled in the wa rmer climate of Toolik Lake. A similar trend was seen in non-breeding birds, but this was not significant. Additionally, in January, baselin e cortisterone levels in males were correlated with body mass, althoug h this relationship did not hold when both sexes were considered. Body mass and fat score in winter were similar to those of redpolls sample d at Barrow in June. These data suggest that redpolls may be able to a djust their responsiveness to acute stresses in relation to fat stores . Those with greater fat depots had reduced responsiveness to stress. (C) 1994 Wiley-Liss, Inc.