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European Roe Deer Faecal Hormone Metabolites Varied With Season and Local Environment

Male European roe deer resting in woodland in De Veluwezoom National Park
Research · Physiology

A study of European roe deer (Capreolus capreolus) in northern Iran found that hormone metabolites in faeces varied with season and local environmental conditions. Researchers collected 50 fresh faecal samples during 2023–2024 in Kiasar National Park and the Dodangeh-Chahardangeh Wildlife Refuge in Mazandaran Province.

Hormone metabolites are breakdown products produced as the body processes hormones and then excretes them. Measuring them in faeces allows hormone activity to be studied without capturing or taking blood from the animal, but the samples in this study were not assigned to individually known deer. Sex was estimated from pellet shape together with testosterone and progesterone metabolite patterns rather than confirmed genetically, so sex-specific results refer to samples classified by this method.

Cortisol metabolites were lowest in summer

Faecal cortisol metabolites — breakdown products of a glucocorticoid involved in the body’s physiological response to energetic and environmental demands — were lowest in summer. Samples classified as male had higher concentrations than female-classified samples, and concentrations increased with NDVI.

NDVI is a satellite-derived measure of vegetation greenness: higher values indicate more photosynthetically active green vegetation, but do not by themselves mean that habitat is better for roe deer. Cortisol-metabolite concentrations showed no supported relationship with elevation, monthly temperature or precipitation in the final model.

Reproductive-hormone metabolites also varied

Testosterone metabolites in male-classified samples varied seasonally and declined as elevation and NDVI increased. Progesterone metabolites in female-classified samples peaked in summer and showed no supported relationship with elevation or vegetation greenness in the final model.

The researchers also found no clear correlation between cortisol and testosterone metabolites in male-classified samples or between cortisol and progesterone metabolites in female-classified samples. In this dataset, higher glucocorticoid-metabolite concentrations therefore did not systematically coincide with higher or lower reproductive-hormone metabolite concentrations.

The study has important limits. Only 50 samples were collected across the year, sex was estimated rather than genetically verified, and the commercial enzyme immunoassay used for cortisol metabolites was not biologically validated in roe deer by testing whether it detects a known increase in adrenal activity. The authors therefore caution that faecal glucocorticoid metabolites should not be treated as a direct measure of “stress” on their own. Larger seasonal samples and species-specific validation are needed before the method can be used as a precise physiological stress indicator.

Sources and image credit

  1. Amininasab, S. M., Ansari Pirsaraei, Z., & Yousefpour Bisheh, A. (2026). The relationships of season, climate, habitat, and sex variables with fecal cortisol, progesterone, and testosterone metabolite concentrations in roe deer. Ecology and Evolution, 16(6), e73712. https://doi.org/10.1002/ece3.73712Primary peer-reviewed open-access article first published 31 May 2026 under CC BY 4.0. Researchers analysed 50 fresh faecal samples collected during 2023–2024 from European roe deer in Kiasar National Park and the Dodangeh-Chahardangeh Wildlife Refuge in northern Iran.

Image: Bouke ten Cate / Wikimedia Commons — male European Roe Deer photographed in De Veluwezoom National Park, the Netherlands, 18 May 2021; representative species image, not from the Iranian study · CC BY 4.0 · Source

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