Intra‐annual variation of fecal nitrogen of red deer in Mediterranean habitats and its relationship with NDVI and bioclimatic indices

Abstract Understanding diet quality is essential for wildlife ecology and management, especially in Mediterranean ecosystems where forage quality varies markedly throughout the year. Fecal nitrogen is a widely used non‐invasive indicator of ungulate diet quality, though its collection and analysis can be resource‐intensive. To address this, environmental proxies like the normalized difference vegetation index (NDVI) and bioclimatic indices (e.g., real bioclimatic intensity [RBI], standardized precipitation‐evapotranspiration index [SPEI]) have been proposed as scalable alternatives. This study evaluated the spatial and intra‐annual variation of fecal nitrogen in a fenced Mediterranean estate in central Spain and its relationship with NDVI at different scales and bioclimatic indices. Fecal nitrogen showed significant intra‐annual variability aligned with seasonal changes in forage quality but no spatial differences across local habitats. The NDVI derived from herbaceous vegetation, open forests, and whole‐estate scales explained monthly fecal nitrogen variation, whereas NDVI from Mediterranean woodlands did not. We did not find evidence of relationships between fecal nitrogen and RBI or SPEI. These findings highlight that the fecal nitrogen–NDVI relationship is scale‐dependent and that herbaceous NDVI is a reliable proxy for tracking diet quality in Mediterranean red deer populations.