Validation of Fecal Glucocorticoid Metabolites as Non-Invasive Markers for Monitoring Stress in Common Buzzards (Buteo buteo)

Abstract

For wild animals, being in captivity in wildlife centers can cause considerable stress. Therefore, it is necessary to establish and validate non-invasive tools to measure chronic stress during rehabilitation. Eight Common Buzzards which lived in permanent husbandry were placed individually into prepared aviaries and their feces were collected before, during and after a stress event for biological validation over a period of seven days. The extracted fecal glucocorticoid metabolites (fGCMs) were analyzed with three different enzyme immune assays (EIA) to find the most suitable one. Additionally, we aimed to investigate the stability of fGCM levels after defecation because further metabolization by bacterial enzymes can lead to changed results. The Cortisone-EIA performed best in males and females and showed that the stress event led to an fGCM increase of 629% (557% in females and 702% in males) in relation to basal values. We found no significant differences between the sexes, but observed significant differences between different times of day. FGCM concentration significantly changed after eight hours at room temperature. Our study successfully validated the non-invasive measurement of fGCM as a stress indicator in Common Buzzards and could therefore lay the foundation for future studies providing new insights for animal welfare research in Buzzards.

Keywords: animal welfare; behavior; bird of prey; corticosterone; fGCM; hormone; rehabilitation; wildlife.

Figure 1

Fecal glucocorticoid metabolite (fGCM) concentrations in ng/g dry weight (DW) of female Buzzards: F1, F2, F3 (n = 3) before and after stress event. Missing data points are due to missing or insufficient fecal samples.

Figure 2

Fecal glucocorticoid metabolite (fGCM) concentrations in ng/g dry weight (DW) of male Buzzards: M1, M2, M3 (n = 3) before and after stress event. Missing data points are due to missing or insufficient fecal samples.

Figure 3

Variation in fecal glucocorticoid metabolite (fGCM) levels after the stress event in relation to the individual baseline (all values before the stress event are set to the average 100%). Male Buzzards: M1, M2, M3 and female Buzzards: F1, F2, F3. Missing data points are due to missing or insufficient fecal samples.

Figure 4

Comparison of fecal glucocorticoid metabolite (fGCM) levels in ng/g dry weight (DW) between the sexes.

Figure 5

Diurnal variation in fecal glucocorticoid metabolite (fGCM) levels in ng/g dry weight (DW). Significant differences between times of day are indicated by different letters.

Figure 6

Post-defecation changes of immunoreactive fecal glucocorticoid metabolite (fGCM) levels in ng/g dry weight (DW) induced by degradation. Significant differences in comparison to the control 0 are indicated by asterisks (Dunnett’s test, *** = highly significant (p ≤ 0.001)).