The migration-breeding transition: integrating behavior, stress physiology and fitness from a long term data set (#92)
The transition from migration to breeding requires major changes in physiology and behavior. Many long-distance migrants need to be highly flexible during this transition, given the disconnect between conditions on the wintering grounds and at the breeding site. Arrival at the breeding site may be followed by immediate initiation of nesting (in mild years), or an extended wait for nest sites to become available (in more extreme years). The mountain white-crowned sparrow faces highly variable conditions on arrival at the breeding site: nest initiation dates varied by 6 weeks over a 15 year period, due to changes in winter snow pack and spring temperatures. I have studied the arrival biology of the mountain white-crowned sparrow for 15 years, evaluating the role of stress physiology in behavioral transitions from migration into nesting. In this presentation I will discuss data demonstrating that glucocorticoids extend flexibility during this migration/breeding transition: as winter-like conditions persist on the breeding site, glucocorticoids reverse the usual increased focus on the nesting site; higher glucocorticoids are associated with earlier territorial abandonment; and, exogenous glucocorticoids induce movement away from the breeding site down to lower elevation staging areas. Taken together, this glucocorticoid-induced increase in flexibility may enhance survival in years with more inclement weather.