Sex differences in the long-term repeatability of the acute stress response in long-lived, free-living Florida scrub-jays (Aphelocoma coerulescens)
There is increasing evidence that individual differences in the physiological stress response are persistent traits in many animals. To test the hypothesis that the stress-induced CORT (SI-CORT) response is repeatable over the adult life span of Florida scrub-jays (Aphelocoma coerulescens), we sampled 32 male and 25 female free-living scrub-jays (aged 2–13 years) during a 9-year period (2004–2012). Each individual was sampled two to five times and samples were collected one or more years apart during the pre-breeding season (Jan–March). In addition, individuals sampled over the greatest time period (6–8 years) were analyzed separately to more closely assess long-term repeatability. SI-CORT was repeatable in females, but not males, when values were not corrected for confounding variables (agreement repeatability). However, when the year and time of day of sample collection were controlled (adjusted repeatability), SI-CORT was repeatable in both sexes. SI-CORT was also repeatable in the males and females sampled 6–8 years apart. Finally, baseline CORT levels of males, but not females, exhibited low but significant repeatability when adjusted for year. The results of this study demonstrate that differences in SI-CORT levels were repeatable within adult scrub-jays sampled up to 8 years apart. Further, the female SI-CORT response was more consistent between pre-breeding seasons than males, which may have resulted from males having higher SI-CORT plasticity in response to environmental conditions. These data support the hypothesis that the SI-CORT response of Florida scrub-jays develops before adulthood and persists throughout much, if not all, of their natural adult life span.