A Long-Term Study of Food-Niche Dynamics in the Common Barn-Owl: Comparisons within and Between Populations

Food niches of Common Barn-Owl (Tyto alba) populations were studied for 8 years in Utah and Idaho. Small mammals dominated the diet as they do in most parts of the barn-owl's range. Mean prey weight was nearly identical between the two owl populations. Food-niche breadth, though, was significantly broader in Idaho than in Utah. Food-niche breadth was also more variable in Idaho than in Utah both within and between years. Voles (Microtus spp.) were predominant prey for both owl populations and were the only prey whose numeric variation in the diet significantly affected mean prey weight and food-niche breadth. Vegetative composition was less varied and more uniformly favorable to voles in Utah. The Idaho area contained a smaller poportion of good vole habitat but had a greater diversity of vegetation including deserts suitable for small mammal species not found in the Utah study area. These vegetative differences and their effects on small mammal species diversity and density were the most apparent causes of food-niche differences between the two owl populations.