Abstract
Some predators depend heavily on one or a few prey types, and others have exceptionally broad diets. It is unclear how this diet variation arises. Here, we demonstrate a strong link between diet species richness and Shannon entropy of prey frequencies (a diet diversity spectrum) for a globally distributed group of apex predators-raptors. For many raptors, diet entropy is consistent with random sampling expectations given a lognormal distribution of abundances among prey species. Yet most species-rich diets often approach the maximum possible diet entropy, indicating an unexpected level of diet evenness that is not predicted by theory. Positioning along this diet diversity spectrum is linked to evolutionary history, the types of prey that are acceptable and the role of raptors as food web integrators through cross-habitat sampling. These results suggest that raptors may have a highly stabilizing effect on terrestrial food webs and play an important role in maintaining biodiversity.