The Seasonal Diet Selection and Nutritional Niche of Mule Deer in a Chihuahuan Semi-Desert

Ruminant herbivores interact dynamically with their food resources, especially in deserts, where plant availability fluctuates sharply across seasons. We evaluated how seasonal food availability and the nutritional traits of preferred plants shape the diet and macronutrient niche of a desert mule deer (Odocoileus hemionus) population in the buffer zone of the Médanos de Samalayuca protected area, northern Mexico. From 2021 to 2022 we quantified seasonal food plant availability and characterized mule deer diet using microhistological fecal analysis and the nutrient content by right-angled mixture triangles. Mule deer diets were consistently low in diversity and dominated by grass, but preferred species shifted seasonally among shrubs, succulents, and grasses. Deer strongly selected some plant species that were scarce in the landscape, particularly during the cold-dry season. Preferred plants generally had high carbohydrate and variable protein contents, with the highest protein proportions in the temperate-dry season. Mixture triangles showed a narrow, carbohydrate-biased macronutrient niche, with the broadest range of nutrient mixtures in the temperate-dry season. Overall, our results support an opportunistic foraging strategy in which mule deer consume what is seasonally available while selectively using key plant species to maintain a relatively constant nutritional balance under limited and variable food resources.