Both Eltonian variables, such as behavior and diet, and Grinnellian axes, such as environmental conditions, are required to describe the structure of species’ ecological niches and address unresolved questions about species distributions and coexistence dynamics. We observed two closely related and morphologically similar East African hornbills, Tockus deckeni and T. erythrorhynchus, at multiple sites within their sympatric distribution. We combine high-resolution remotely sensed imagery and detailed observations of behavior, diet, and movement patterns, to evaluate a priori expectations about niche volume and overlap for these two species.
Tockus hornbills exhibited significant differences along several measured niche axes. Tockus erythrorhynchus spent more time on food-related activities, and perched and foraged closer to the ground. In contrast, T. deckeni foraged at a wider range of vertical heights, and consumed a more varied diet. The magnitude of interspecific variation differed by range position (i.e. study site). Such partitioning along multiple niche axes likely reduces interspecific competition, consistent with the principle of limiting similarity. East Africa harbors a large number of bird species; explanations for interspecific coexistence in this region likely include niche volume and partitioning dynamics.