The relationship between fitness and baseline glucocorticoids in a passerine bird

摘要: Glucocorticoid (cort) hormones are increasingly applied in studies of free-ranging animals, with elevated baseline cort levels generally assumed to indicate individuals or populations worse condition and lower fitness (the Cort-Fitness Hypothesis). The relationship between is rarely validated investigating the cort-fitness often find results inconsistent Hypothesis. inconsistency these may result part from variation across life history stages. Here we address following questions a two-year study tree swallows (Tachycineta bicolor): (1) Do correlate within stage? (2) Does vary different stages? (3) stages an individual? (4) reproductive effort influence levels, do effort? We measured components female birds known breeding correlations some stages, but shifts negative during early positive late breeding, even same individuals. A nestling period suggests that investment elicit higher feedback reallocate more reproduction critical periods provisioning. Our findings provide reason question Hypothesis, have implications for application measures monitoring conservation concern.