Covariation among glucocorticoid regulatory elements varies seasonally in house sparrows

► We studied variation and covariation in the hypothalamic-pituitary-adrenal axis in a wild bird. ► Hormone levels and receptor density were examined during breeding and molt. ► CORT (baseline, after a stressor, after negative-feedback) was lowest during molt. ► CORT release was positively correlated with negative-feedback and mineralocorticoid expression.