Fig. 2.

Urinary cortisol (uCortisol) variation by age, sex, and reproductive effort. uCortisol concentrations are the residual from time of day, after correction for urine specific gravity and log transformation. (A) While each sex produces more cortisol as they age and males (blue dashed line, n = 8,029 samples, 20 individuals) produce significantly higher levels than females (red solid line, n = 7,888, 39 individuals), the age effect was statistically similar between males and females. (B) Males produce more cortisol on days when they are in association with at least one parous, swollen female (dashed line) than on days when they are not (solid line), but the effect of age is reduced when parous, swollen females are present. (C) Females exhibit higher overall cortisol production and a steeper increase with age when they are cycling (green dotted line: cycling with maximal swelling; red solid line: cycling without maximal swelling) than when in early lactation (aqua dot-dashed line: first 2 y after parturition) or late lactational amenorrhea (purple dashed line). Shaded bands indicate 95% CIs.