Abstract
The measurement of cortisol in hair is becoming important in studying the role of stress in the life history, health and ecology of wild mammals. The hair cortisol concentration (HCC) is generally believed to be a reliable indicator of long-term stress that can reflect frequent or prolonged activation of the hypothalamic-pituitary-adrenal axis over weeks to months through passive diffusion from the blood supply to the follicular cells that produce the hair. Diffusion of cortisol from tissues surrounding the follicle and glandular secretions (sebum and sweat) that coat the growing hair may also affect the HCC, but the extent of these effects is thought to be minimal. In this study, we report on a range of factors that are associated with, and possibly influence, cortisol concentrations in the hair of free-ranging brown bears (Ursus arctos). Through two levels of analyses that differed in sample sizes and availability of predictor variables, we identified the presence or absence of capture, restraint and handling, as well as different methods of capture, as significant factors that appeared to influence HCC in a time frame that was too short (minutes to hours) to be explained by passive diffusion from the blood supply alone. Furthermore, our results suggest that HCC was altered after hair growth had ceased and blood supply to the hair follicle was terminated. However, we also confirmed that HCC was inversely associated with brown bear body condition and was, therefore, responsive to diminished food availability/quality and possibly other long-term stressors that affect body condition. Collectively, our findings emphasize the importance of further elucidating the mechanisms of cortisol accumulation in hair and the influence of long- and short-term stressors on these mechanisms.
Highlights
Stress is increasingly recognized as an influential factor in the life history, health and ecology of wild animals
Even when we constrained the coarse-level analysis to data collected only during the years of the Alberta Grizzly Bear DNA Inventory, 2004– 08, the median hair cortisol concentration (HCC) for bears captured by remote drug delivery from helicopter or by leg-hold snare was 2.5 times greater than that for free-ranging bears sampled by barbed wire, whereas the median HCC for bears captured by culvert trap was seven times greater
Stenhouse, unpublished observations) on the haematology and serum biochemistry of brown bears, in which we have found that two markers of short-term or acute stress, the neutrophil-to-lymphocyte ratio and serum total cortisol, show values in bears captured by culvert trap to be intermediate to the higher values in bears captured by leg-hold snare and to the lower values in bears captured by remote drug delivery from helicopter
Summary
Stress is increasingly recognized as an influential factor in the life history, health and ecology of wild animals. These include studies of oxidative damage (Monaghan et al, 2009; Selman et al, 2012), telomere dynamics (Barrett et al, 2013; Mizutani et al, 2013), fluctuating asymmetry (Allenbach, 2011; SánchezChardi et al, 2013) and changes in body mass or body condition (Hodges et al, 2006; Sheriff et al, 2011b) All these studies, irrespective of whether stress is considered as a response or an effect, require robust indices of stress that are sensitive to changes in stressor frequency and intensity, and that can be interpreted in the face of confounding factors, e.g. age, sex, season. This means that these indices should be fully validated to ensure an acceptable degree of accuracy and precision in their application and interpretation (Sheriff et al, 2011a; Johnstone et al, 2012)
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