Experimental relationships between levels of corticosterone in plasma and feathers in a free-living bird

Abstract

SUMMARYIntegrated measures of corticosterone (CORT), such as from feathers (CORT f ), have intuitive appeal because they incorporate both the duration and amplitude of glucocorticoid secretion. An association between CORT f and plasma CORT has never been shown in wild birds, and it is unclear as to when and whether these measures should be correlated, given that they are fundamentally different yet related measures of physiology. We hypothesized that CORT f should correlate with instantaneous measurements of plasma CORT when the latter reflect sustained changes in the activity of the hypothalamic-pituitary-adrenal (HPA) axis. To test this, we experimentally manipulated levels of plasma CORT in wild nestling tree swallows (Tachycineta bicolor) using 5day time-release CORT pellets, and measured plasma CORT and growth parameters before, during and at the end of hormone manipulation (days 7, 9 and 11 post-hatch, respectively). CORT f and plasma CORT were significantly positively related only when the latter was at its highest and most variable among individuals (day 9). A similar relationship was expected at day 11, but plasma CORT had returned to near-original levels. Nestlings with higher CORT f were smaller, lighter and less likely to fledge, but we did not detect seasonal effects on CORT f . Our results clearly demonstrate that CORT f from free-living birds can reflect plasma CORT, but correlations may not always be expected, especially if elevations in plasma CORT are relatively modest and of short duration. Our work suggests that CORT f is best used to study the activity of the HPA axis over relatively long time frames and can be used effectively to advance avian ecology. Supplementary material available online at

Evaluating the Stress Response as a Bioindicator of Sub-Lethal Effects of Crude Oil Exposure in Wild House Sparrows (Passer domesticus)

“…It takes several weeks to complete feather growth. During most of this period, plasma CORT will be at normal baseline concentrations, with only occasional elevations due to stressor exposure [51]. We saw no difference in baseline CORT titers between birds on an oiled diet compared to controls, so feather CORT may reflect baseline CORT more than stress-induced CORT.…”

Feather corticosterone reveals developmental stress in seabirds

“…Previous studies have also found baseline plasma CORT to be a non-significant correlate with feather CORT, which was instead significantly positively correlated with stress-induced CORT (Bortolotti et al, 2008;Patterson et al, 2014). Feather CORT may, therefore, be a more robust method of detecting exposure to environmental stressors that vary in duration and intensity (see also Fairhurst et al, 2013). Like measuring the stress-induced CORT response (Kitaysky et al, 2007;Kitaysky et al, 2010), feather CORT might provide a more long-term continuous measure of an individual's exposure to elevated corticosterone, but would do so in a fraction of the handling time, under less duress to individuals and would not have the ability to 'reset' when conditions improved.…”

“…Recently, several studies have employed a technique that measures the amount of CORT contained in feather tissues, which are grown over a period of days or weeks. Several of these studies indicate that the relatively non-invasive sampling of whole feathers may provide an integrated measure of stress incurred throughout the growth of that feather (Fairhurst et al, 2013), and that feathers can be sectioned to obtain a rough profile of stress experienced during feather growth (Bortolotti et al, 2008;Bortolotti et al, 2009;Lattin et al, 2011). The current 'passive deposition' hypothesis predicts that elevated CORT in blood plasma will correspond to higher levels of CORT in feather tissue because the CORT circulating in the blood is incorporated into the feather tissues as they are being formed (although the mechanisms are still unknown) (Bortolotti et al, 2008).…”

“…There is a need to experimentally validate how feather growth rates and feather CORT respond to natural environmental stressors; otherwise, use of this technique may lead to equivocal interpretations of feather CORT results. To date, only a few studies have assessed the technique of measuring CORT in feather tissues of chicks that have experienced experimentally induced stressful conditions during development (Fairhurst et al, 2012b;Fairhurst et al, 2013). …”

Temporal overlap and repeatability of feather corticosterone levels: practical considerations for use as a biomarker

“…To date, multiple studies have shown that feather CORT most often relates to measurements of circulating CORT levels after a standardized stressor rather than those measured at baseline circulating levels (Bortolotti et al ., 2008; Lattin et al ., 2011; Fairhurst et al ., 2013; Jenni-Eiermann et al ., 2015). Although this apparent deposition bias towards stress-induced levels may be attributable to the difference in magnitude between baseline and acute levels (Fairhurst et al ., 2013), it nevertheless calls into question the interpretation of feather CORT as an average of circulating levels during feather growth.…”