Tracking stress: localisation, deposition and stability of corticosterone in feathers

Abstract

All feathers were prepared by first removing the calamus (i.e. the proximal, vaneless portion of the quill) and the length of the remaining portion, or segments of it, was measured and weighed. None of the samples were washed prior to hormone analysis as natural substances such as preen oils were found not to influence the results (Bortolotti et al., 2008). Feathers were stored in ordinary paper envelopes between collection (various years, see below) and analysis (2004)(2005)(2006)(2007)(2008). Understanding what environmental perturbations are perceived as stressors, and quantifying how they are responded to, how often they occur and the negative consequences of exposure to glucocorticoids, has been problematic and limited to short-term physiological measures. By contrast, the quantification of corticosterone (CORT) in feathers represents a long-term, integrated measure of hypothalamic-pituitary-adrenal activity. In the present study, we show that by understanding how the hormone is deposited in feathers, in combination with specific sampling protocols, one can identify localised patterns of CORT deposition that reveal different temporal patterns of a bird's response to stressors. CORT in feathers appears to be stable over time, is resistant to heat exposure and is useful in determining both the overall exposure of the bird to the hormone over days or weeks, as well as identifying discrete, punctuated, stressful events. Variation in feather CORT can also be examined among individuals of a population at one point in time, as well as over years by using museum specimens. The ability to track stress over time allows for new questions to be asked about the health and ecology of birds and their environment.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

“…Feather hormone concentrations were expressed as pg mm -1 of feather (Bortolotti et al, 2008(Bortolotti et al, , 2009. Two 100 µl aliquots of a pool of feather extracts were included with each RIA to assess inter-and intra-assay variation.…”

“…Compelling reasons for quantifying feather steroid hormone content as a time-dependent unit (mass of hormone per unit length; pg mm -1 ) rather than mass-dependent unit (pg mg -1 ) have been presented elsewhere (Bortolotti et al, 2009;Bortolotti, 2010). The primary rationale for this approach is to avoid artifacts arising from variation in mass between feathers, potentially resulting in mass dilution of the deposited/sequestered steroid.…”

“…Furthermore, there is no evidence that the CORT content of feathers declines with time after collection making possible the analysis of steroid hormone concentrations in feather samples from long-term archives and museum collections (Bortolotti et al, 2009;Kennedy et al, 2013). A significant caveat in the use of feathers as a source of steroid hormone data is that the uptake of CORT by feathers is, as noted above, considered to occur during the growth phase of the feather only, and therefore the period during which CORT is accumulated may be at some remove from the time at which somatic or contaminant data may be collected.…”

Parasites, mate attractiveness and female feather corticosterone levels in a socially monogamous bird

“…Upon recapture, we collected a growing rump feather from each female for corticosterone assays (Bortolotti et al 2009a). We collected rump feathers that were almost fully grown (c. 90 % of a fully grown size), but that were still growing (i.e.…”

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

“…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.…”