# Stable Isotope Analysis Reveals Habitat-Driven Dietary Niches of Lepus europaeus

## TL;DR

Stable isotope analysis shows European brown hares in diverse habitats have broader diets than those in uniform farmland, suggesting habitat diversity supports healthier hare populations.

## Contribution

This study uses stable isotope analysis to demonstrate that habitat heterogeneity, not demographic factors, drives dietary flexibility in European brown hares.

## Key findings

- Hares in Lithuania's diverse landscapes had broader diets compared to those in Poland's orchard areas.
- Isotopic analysis revealed no dietary differences between male, female, young, and old hares.
- Promoting mixed cropping and diverse habitats could improve food quality and support hare populations.

## Abstract

The European brown hare (Lepus europaeus) is a common inhabitant of open fields and farmlands. However, its population has declined across Europe due to changes in agriculture. Modern large-scale farming has reduced the variety of plants and habitats on which hares depend for food and shelter. In this study, we examined the diets of hares in Lithuania and Poland by analyzing stable isotopes in their hair. Differences in carbon and nitrogen values can serve as a proxy for hare diets. We found that hares living in Lithuania’s varied landscapes had a broader diet than those in Poland’s orchard areas, which had a more limited range of foods. Male and female hares, as well as young and old ones, had similar diets. Our results indicate that diverse farmland with different crops, grassy areas, and shrubs provides better feeding opportunities for hares. Promoting such landscape diversity can support healthy hare populations and more balanced farmland ecosystems.

Understanding the trophic ecology of the European brown hare (Lepus europaeus) is essential for its conservation in intensifying agricultural landscapes. To explore dietary niches across habitats, sexes, and age groups, we applied stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) in hair samples from 151 hares collected in Lithuania and Poland from 2023 to 2025. δ13C and δ15N values varied significantly by country and habitat, but not by sex or age. Lithuanian hares exhibited lower δ13C values and a wider isotopic niche, reflecting more diverse foraging in heterogeneous habitats. In contrast, Polish hares from uniform orchard landscapes showed higher δ13C enrichment and narrower isotopic ranges, indicating greater dietary specialization on cultivated plants. Temporal variation was minimal, and isotopic overlap among months and years was high. These results suggest that habitat heterogeneity, rather than demographic factors, drives dietary flexibility in L. europaeus. Thus, stable isotope analysis provides a powerful tool for linking agricultural land use with trophic niche breadth in farmland mammals. Promoting mixed cropping systems, permanent vegetation, and structurally diverse habitats could improve food quality and support the recovery of declining hare populations.