LYNN, S.E.; HUNT, K.E.; WINGFIELD, J.C.; Colby College; University of Washington; University of Washington: The adrenocortical response to stress in grassland birds: reexamining ecological influences on the stress response during breeding

Environmental perturbations lead to a rise in circulating corticosterone (CORT) in breeding birds, which affects behavior patterns that can maximize survival. However, an individual�s response to acute stress is associated with a trade-off between current and future reproduction: an individual can either increase CORT, thereby activating behavior associated with abandoning the current reproductive effort, or suppress CORT secretion and potentially risk death by attempting to continue the current reproductive effort. Which pattern an individual exhibits appears to relate to certain ecological variables. For example, three commonly cited hypotheses suggest that during breeding, a suppressed CORT response to a stressor may be advantageous for 1) the sex that is most important for parental care, 2) individuals in good body condition, and 3) species with a short breeding season and limited renesting opportunities. We evaluated CORT secretion during 1-h of handling in Chestnut-collared and McCown�s longspurs (Calcarius ornatus, C. mccownii), species that breed at mid-latitudes, and have congeners that are exclusively arctic breeders. We use our data to address these hypotheses both within a phylogenetic framework and across environmental variables. In both mid-latitude species, CORT secretion in response to handling was similar between the sexes, and was unrelated to body condition. Additionally, although more renesting opportunities exist at mid-latitudes than in the Arctic, CORT secretion was similar among congeners. We suggest that an attenuated stress response may relate to the severity of the breeding environment and a low likelihood of successful renesting, as these variables are common to both Arctic and grassland habitats.