Seasonal glucocorticoid responses to capture in wild free-living mammals

Abstract

We determined baseline and capture-induced glucocorticoid concentrations during two different seasons in three species of wild free-living rodents: brown lemmings (Lemmus trimucronatus), golden-mantled ground squirrels (Spermophilus saturatus), and yellow-pine chipmunks (Tamias amoenus). Initial blood samples were obtained within 3 min of capture, so that initial glucocorticoid levels reflect baseline titers of undisturbed animals. Animals were held for an additional 30 min, when a second blood sample was taken to measure stress-induced glucocorticoid titers. The primary glucocorticoid differed in each species. Lemmings secreted extremely large amounts of corticosterone (as high as 8,000 ng/ml). These high concentrations were accompanied by high corticosterone-binding globulin capacity and resistance to negative feedback. Squirrels and chipmunks secreted a mixture of cortisol and corticosterone (10-400 ng/ml). In males of all three species and female squirrels and chipmunks, glucocorticoid levels were significantly elevated 30 min after capture. Baseline and 30-min glucocorticoid levels differed seasonally in each species. Levels were higher during summer (with no snow cover) than in spring (with approximately 60% snow cover) in female lemmings, higher during breeding than before hibernation in squirrels, and higher postreproductively than during breeding in chipmunks. Together, these data indicate that glucocorticoid responses to stress in these free-living species are similar to those in laboratory species, but the magnitude of the response appears to depend on life-history features specific to each species.

Measuring stress in wildlife: techniques for quantifying glucocorticoids

“…Both, commercial or in-house immunoassays (RIAs or EIAs) may all have different detection limits. GC levels in wildlife species can range from a few nanograms/millilitre (e.g., many bird species) to thousands/millilitre (e.g., lemmings) (e.g., Romero et al 2008). High concentrations can be diluted, but options for species with low GC concentrations may be more limited.…”

“…Thus the control-a benchmark of what constitutes the 'normal' unstressed condition-may not be readily available. There are now numerous wildlife studies showing that plasma GC levels increase significantly after 2-5 min from capture (e.g., Boonstra and Singleton 1993;Cash et al 1997;Place and Kenagy 2000;Boonstra et al 2001;Romero and Reed 2005;Mueller et al 2006;Wada et al 2007;Romero et al 2008). It is often impractical or impossible to obtain blood samples from wildlife this quickly under field conditions.…”

Endocrine and immunological responses to adrenocorticotrophic hormone (ACTH) administration in juvenile harbor seals ( Phoca vitulina ) during winter and summer

“…Capture and handling methods routinely used during blood collection in wild mammals have been shown to result in elevated cortisol concentrations (Engelhard et al, 2002;Romero et al, 2008;Di Poi et al, 2015) and alter hematological parameters (Castellini et al, 1996;Cattet et al, 2003). However, many studies focused on free-ranging marine mammals have not addressed the potential effect of capture and handling methods on the parameters of interest.…”

No energetic cost of anthropogenic disturbance in a songbird

“…For example, low survival rates were correlated with the increased energy expenditure as a result of increased reproductive effort in European kestrels (Falco tinnunculus; Daan et al 1996). Thus, selection will strongly favour cost-effective strategies that enable organisms to cope with environmental stressors while performing vital reproductive duties (Wikelski & Ricklefs 2001;Wingfield & Sapolsky 2003;Love et al 2004;Berger et al 2007;Romero et al 2008). For example, Wingfield et al (1998) proposed that birds adopt an 'emergency' life-history stage, and abandon reproductive activities, when faced with perturbations in their environment as a means to redirect energy towards survival.…”