Cedric Zimmer, Conor C. Taff, Daniel R. Ardia, Thomas A. Ryan, David W. Winkler, Maren N. Vitousek
Individuals in all species show important variation in the way they deal with stressors. The main way to measure response to stress at physiological level is by measuring circulating stress hormones. Stress hormones increase quickly when facing a stressor and then return to baseline level when the threat disappears. Many studies have aimed at testing the relationship between individual variation in stress hormones level and how individuals cope with stressors. Most of these studies looked at individual differences in stress-induced level (increased level of stress hormones after exposure to a stressor), as prolonged exposure to stress hormones is costly, and did not find consistent results. A part of the stress response that could be important but that has been largely neglected is the decrease of stress hormones after reaching peak level. This decrease is controlled by stress hormones themselves by negatively regulating the stress axis (brain areas regulating the stress response) to shut it down and return to baseline. Effectively terminating the stress response may be important to cope with stressors as it would allow faster recovery and limit the damage associated with exposure to stress hormones.
We sought to determine if individual variation in the different parts of the stress response is associated with how individuals cope with experimental stressors in free-living tree swallows. During incubation, we exposed female tree swallows to two different experimental stressors: a reduction of flight efficiency by temporarily (5 days) attaching together some wings’ feathers in order to increase the cost of foraging, and an increase in perceived predation risk by exposing incubating females to a stuffed mink for 10 seconds every day for 5 days.
We found that females that showed a strong increase in stress hormones within 30 minutes after we caught them in their nest followed by a faster decrease in stress hormones were less likely to abandon their nest in response to our experimental stressors. This suggests that females that exhibited both a strong stress response and an effective termination of this response cope better with stressors. Therefore, the ability to turn on and then off the stress axis efficiently may be important for fitness.