Non-Invasive Assessment of the Interrelationships of Diet, Pregnancy Rate, Group Composition, and Physiological and Nutritional Stress of Barren-Ground Caribou in Late Winter

Abstract

The winter diet of barren-ground caribou may affect adult survival, timing of parturition, neonatal survival, and postpartum mass. We used microhistological analyses and hormone levels in feces to determine sex-specific late-winter diets, pregnancy rates, group composition, and endocrine-based measures of physiological and nutritional stress. Lichens, which are highly digestible but contain little protein, dominated the diet (> 68%) but were less prevalent in the diets of pregnant females as compared to non-pregnant females and males. The amount of lichens in the diets of pregnant females decreased at higher latitudes and as winter progressed. Pregnancy rates (82.1%, 95% CI = 76.0 – 88.1%) of adult cows were within the expected range for a declining herd, while pregnancy status was not associated with lichen abundance in the diet. Most groups (80%) were of mixed sex. Male: female ratios (62:100) were not skewed enough to affect the decline. Levels of hormones indicating nutritional stress were detected in areas of low habitat quality and at higher latitudes. Levels of hormones indicated that physiological stress was greatest for pregnant cows, which faced the increasing demands of gestation in late winter. These fecal-based measures of diet and stress provided contextual information for the potential mechanisms of the ongoing decline. Non-invasive techniques, such as monitoring diets, pregnancy rates, sex ratios and stress levels from fecal samples, will become increasingly important as monitoring tools as the industrial footprint continues to expand in the Arctic.

Costs and benefits of group living in primates: an energetic perspective

“…Additionally, several studies have examined how thyroid hormone levels vary in response to changes in energetic input. In these studies, low thyroid hormone concentrations have been found in periods of food restriction, food shortage and/or low food quality [157][158][159][160][161].…”

“…B 372: 20160239 can avoid these complications by providing a novel approach to non-invasively assessing energetic stress. Faecal determination of thyroid hormone levels has been used to non-invasively assess energetic balance in several diverse species including killer whales, monk seals, caribou and northern spotted owls [154,158,160,165]. Despite this record of success, this technique has only been validated in a few primate species to date [157,159,161].…”

Non‐invasive physiological markers demonstrate link between habitat quality, adult sex ratio and poor population growth rate in a vulnerable species, the Cape mountain zebra

“…Few studies have assessed physiological measures across more than one subpopulation of a wild animal species. Faecal glucocorticoid concentrations have been linked to food availability across barren‐ground caribou ( Rangifer tarandus ) populations (Joly, Wasser, & Booth, ), and to habitat degradation in collared brown lemur ( Eulemur collaris ; Balestri et al., ). However, no study has assessed the relative impact of both ecological and demographic factors on individual physiology across several subpopulations of a single species.…”

“…populations (Joly, Wasser, & Booth, 2015), and to habitat degradation in collared brown lemur (Eulemur collaris; Balestri et al, 2014).…”

Close encounters of the burned kind: Spatiotemporal effects of fire on habitat selection strategies of woodland caribou (Rangifer tarandus caribou) during winter

“…Cold temperatures and deep, hard snow reduce accessibility to forage and result in high energetic costs of travel on and cratering through snow (Fancy and White 1985;Collins and Smith 1991;Schaefer and Pruitt 1991;Schaefer 1996;Johnson et al 2001). These energetic demands are exacerbated by the increasing gestational demands experienced by pregnant caribou (Parker et al 2005;Joly et al 2015), as the majority of fetal mass is accumulated in the final trimester (Robbins and Robbins 1979), roughly aligning with the late winter season (Hegel and O'Donoghue 2015). The quality of late winter habitat may influence calf condition, recruitment, and the survival of juveniles (White 1983;Gaillard et al 1998;Post and Klein 1999;Adams 2003).…”