Corticosterone in feathers is a long‐term, integrated measure of avian stress physiology

Abstract

Summary 1.Stress has pervasive consequences for the well-being of animals. Currently, understanding how individuals cope with stressors is typically accomplished via short-term quantification of blood glucocorticoids released after activation of the hypothalamic-pituitary-adrenal (HPA) axis. 2. We investigated whether the amount of corticosterone (CORT) deposited in growing feathers provides a long-term, integrated measure of HPA activity in birds using captive red-legged partridges Alectoris rufa as a model species. 3. We examined CORT levels in primary feathers induced to grow at the same time as stress series were performed with a capture and restraint protocol. Plasma CORT titres after stress-induced stimulation, but not baseline values, correlated with feather CORT. Feather levels showed the same pattern as plasma of decline across the breeding season, but more severely. 4. For females, CORT in naturally moulted flank feathers was highly and positively correlated with the number of eggs laid in the previous few months, but not clutch size of the following year. For males, the amount of black on a feather, known to be a social signal, was positively correlated with its CORT level. 5. The analysis of feather CORT is a novel methodology that allows for meaningful interpretations of how individuals respond to environmental perturbations and adjust to life-history stages. 6. The analysis of feather hormones has the unique advantages of allowing for experimentation and sampling at any time of the year with minimal investigator-induced impacts and artefacts, and shows the HPA activity of an individual with a flexible time frame from days to months depending on the length of time taken to grow the feather. As this technique can be applied to living or dead birds, or feathers picked up after moult, it provides the ultimate non-invasive physiological measure of considerable benefit in terms of animal welfare and sampling effort.

Feather corticosterone of a nestling seabird reveals consequences of sex-specific parental investment

“…Greater than 92 per cent of the radioactivity was recoverable in the reconstituted samples. For more information about validation, see supplementary appendix S1 in [32].…”

“…The assay had a detectability limit (80% bound) of 14.20 pg per assay tube, but all samples were well above this value. Data values are expressed as pg CORT per mm of feather, which gives a valid estimate of CORT per unit time of feather growth [32,33] (and see [42] for validation). CORT assays were performed at the University of Saskatchewan, Canada.…”

“…(b) Feather CORT analysis Feather CORT assays followed [32]. Briefly, we extracted CORT from feathers using a methanol-based technique.…”

“…Here, we suggest that nestling CORT responses to parental trade-offs can explain the effects seen in chicks from the 2007 Navarro & González-Solís paper [7], and we use an integrated measure of CORT physiology [32,33] from chick feathers collected during their experiment to explore this possibility. Feather CORT values incorporate the amplitude and duration of all CORT secretion, including response to stressors, during the period of feather growth [32,33] and thus represent a biologically relevant measure of CORT secretion [18].…”

“…Feather CORT values incorporate the amplitude and duration of all CORT secretion, including response to stressors, during the period of feather growth [32,33] and thus represent a biologically relevant measure of CORT secretion [18]. We hypothesize that variation in parental investment was experienced by nestlings as variation in a nutritional stressor to which the nestling HPA axis should be sensitive.…”