Faecal cortisol levels in a wild Iberian red deer population are best explained by prior weather conditions

Abstract

The responsiveness of the hypothalamic–pituitary‐adrenocortical axis to stressors is crucial for wild animals to survive and adapt to environmental changes without compromising individual welfare. We analysed the influence of prior weather conditions, seasonality, the influx of ecotourism, and nutrition on stress levels in a wild population of red deer in a Mediterranean hunting reserve in the Pre‐Pyrenees, Spain. We used faecal cortisol metabolites as a proxy for physiological and psychological stress, and faecal triiodothyronine metabolites as an indicator of nutritional stress. Faecal analyses were chosen because it is a non‐invasive technique that does not alter an individual's behaviour, and it is easy to conduct in a wild population, something which presents added challenges due to the lack of a controlled environment. Our results indicate that prior weather conditions, rather than just seasonality, best explained the variations in these hormones within seasons and among years. On the contrary, the results showed that high levels of the cortisol hormone did not necessarily correspond to low levels of the triiodothyronine hormone. This could be a sign of acute nutritional stress in this population. Finally, we did not find an effect of the ecotourism influx on cortisol levels, suggesting that this deer population tolerates the presence of tourists.

Fecal thyroid hormone metabolites in wild ungulates: a mini-review

“…In general, in examined manuscripts, FTM levels were inversely related to temperature, with higher values in colder periods ( 3 , 7 , 39 ), as physiologically expected. Moreover, FTMs increased in younger subjects and decreased with age for all reviewed cases ( 42 , 47 ).…”

“…Only one study correlated the FTMs to body condition and three to nutritional status. No correlation was found for body condition ( 47 ), while contradictory results were found for nutritional status: one manuscript reported no correlation ( 3 ), one a negative correlation ( 46 ) and another one a positive correlation ( 39 ). Severe conditions such as increased/decreased precipitation or extreme temperature could be responsible for this variability ( 39 ).…”

“…In the reported studies, FTM fluctuations were investigated both in relation to individual and environmental variables. Among the first, age, sex, and nutrition were investigated ( 3 , 7 , 39 , 42 , 46 , 47 ). Regarding the effect of age on FTM concentrations, the results agreed in finding higher levels in juveniles compared to adults ( 42 , 47 ).…”

“…Therefore, as consequence of nutritional deficit, the metabolism tends to slow down, allowing the body to conserve its energy. Given the correlation between THs and body fat, the THs can be considered as an index of body condition ( 38 ), helping to discriminate between nutritional stress and other sources of stress ( 39 ).…”

“…Moreover, FTMs increased in younger subjects and decreased with age for all reviewed cases ( 42 , 47 ). The relationships between FTMs and FCMs ( 3 , 39 , 41 , 46 ), and the characteristics of the intestinal microbiota ( 43 , 44 ) showed contradictory results. Concerning parasites ( 46 ), a negative correlation was found.…”