Use of hair cortisol analysis for comparing population status in wild red deer (Cervus elaphus) living in areas with different characteristics

We tested a method to measure Hair Cortisol Concentration (HCC) in 174 red deer (Cervus elaphus) culled in the hunting season 2011/12 in four areas of Central Italian Alps, with different population densities (SPN, 11.8 deer/km2; HD-AV, 3.6 deer/km2; HD-SO, 2.1 deer/km2; HD-MO, 2.0 deer/km2) and environmental conditions. Our hypothesis was that higher population densities, associated with more difficult environmental conditions, may result in higher allostatic load for these wild ungulates. No significant differences in HCC were detected between sexes (males, 4.77 ± 0.69 pg/mg; females, 5.75 ± 0.63 pg/mg) nor among age classes (calves, 6.17 ± 0.66 pg/mg; yearlings, 4.47 ± 0.83 pg/mg; adults, 5.15 ± 0.74 pg/mg; least square mean ± SE), but HCC difference between calves and yearlings was close to statistical significance (P = 0.059). HCC showed high individual variation, but on average it was higher in areas with higher deer density (SNP, 7.45 ± 1.01 pg/mg; HD-AV, 6.07 ± 0.89 pg/mg; HD-SO, 4.67 ± 1.14 pg/mg; HD-MO, 2.87 ± 1.56 pg/mg), with significant differences between HD-AV and HD-MO (P = 0.01). Carcass weight was significantly lower in SNP (46.74 ± 1.49 kg) than in HD-MO (62.71 ± 4.01 kg), HD-SO (61.73 ± 2.9 kg) and HD-AV (62.07 ± 2.04 kg) (P < 0.001). These results seem to confirm our hypothesis that allostatic load is higher in areas with higher density and harder environmental conditions. We suggest that the methodology used in this study to measure HCC provides good information on long-term HPA axis activity and allostatic load and constitutes a highly promising, reliable and non-invasive method in wildlife management for assessing HPA axis activity over extended time periods.