Measuring corticosterone in feathers: Strengths, limitations, and suggestions for the future

Abstract

The recently introduced technique of measuring corticosterone in feathers currently provides the longest-term measure of corticosterone in birds. This review examines the strengths, weaknesses, and unresolved technical issues of the feather corticosterone technique. Feather corticosterone's major strengths are that it provides: a retrospective assessment of corticosterone physiology, including information from absent (unseen) or dead (e.g. museum specimens) individuals; a long-term measure of corticosterone exposure over the period of feather growth (days-weeks), integrating both baseline and responses to stressors; and flexible, minimally-invasive, sampling. However, researchers considering this technique should be aware of its limitations. Feather corticosterone only reflects hormone exposure during feather growth and, when sampling during molt, corticosterone titers and ecological conditions may not be representative of the majority of the annual cycle. Synchronization of molt is often unknown for a population, requiring assumptions when making inter-individual comparisons. Additionally, unresolved technical issues include: assessing whether corticosterone is the only hormone measured by assays; determining deposition dynamics to fully understand connections between feather and plasma corticosterone titers; studying the longevity and stability of corticosterone in the feather; establishing the impact of feather size and color on corticosterone deposition; and understanding the causes and implications of corticosterone variation along the length of the feather. Notwithstanding the above limitations and technical challenges, determining corticosterone titers in feathers is proving to be a useful technique for exploring some ecological and physiological correlates in individual birds. Given the unique perspective that feather corticosterone offers, we suggest that this measure complement, not replace, plasma measurements.

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

“…However, it is not clear how differences among individuals in their ability to down-regulate hypothalamic–pituitary–adrenal activity or how the current gaps in our understanding of the exact deposition of CORT into feathers (e.g. plasma levels of CORT are in the nanogram range, whereas levels in feathers are in the picogram range; Romero and Fairhurst, 2016) may complicate the interpretation of CORT in feathers grown during natural moult. For example, Done et al .…”

“…Of these, hormone extraction from feathers is a promising, but currently less understood method (Bortolotti et al ., 2008). In particular, determining the mechanisms of corticosterone (CORT) deposition into feathers, the specificity of assays/antibodies, hormone stability over time, mass dependency, influences of feather colour and type, and variation in CORT along feather length are all necessary in order to understand fully how to interpret feather CORT levels within and across individuals (Lattin et al ., 2011; Jenni-Eiermann et al ., 2015; Berk et al ., 2016; Romero and Fairhurst, 2016). …”

“…It should also be noted that while feather CORT should be consistent across feathers, it is not required to have equal levels in absolute terms, as differences in size, shape, colour, structure and growth rate could result in different levels per unit of length (Jenni-Eiermann et al ., 2015; Patterson et al ., 2015; Romero and Fairhurst, 2016). Lattin et al .…”

Physical condition and stress levels during early development reflect feeding rates and predict pre- and post-fledging survival in a nearshore seabird

“…While corticosterone levels in blood plasma can be elevated by short-term factors, such as stress resulting from capture (Love et al ., 2003; Romero and Reed, 2005), corticosterone in avian feathers provides a more sustained record of stress levels over days or weeks (Bortolotti et al ., 2008; Harms et al ., 2010; Romero and Fairhurst, 2016). Feather corticosterone measurements allow for direct comparison of long-term nestling stress levels between different breeding habitats, where variations in nutrition, contamination, predation and parental attendance may affect chronic chick stress even if no outward physical differences are apparent (Bortolotti et al ., 2009; Harms et al ., 2010).…”

Analysis of cortisol in dog hair - a potential biomarker of chronic stress: a review

“…Assessment of long-term glucocorticoid concentrations in various studies has included different keratinised tissues such as hair (Van Uum et al 2008;Veronesi et al 2015;Yamanashi et al 2016), hoof (Comin et al 2014), claws (Veronesi et al 2015), balleen plates (Hunt et al 2014), turtle claws (Baxter-Gilbert et al 2014) and feathers (Romero and Fairhurst 2016). In feathers, corticosterone is measured; the concentration of corticosterone deposited is correlated with the stresses experienced by the bird during feather growth (Romero and Fairhurst 2016). Mammalian nail contains a keratinised epithelium with a vascularised inner corium, where cortisol passively accumulates from the bloodstream (Mack and Fokidis 2017).…”