Diversity in owls’ (Strigiformes) hindlimbs: evolutionary and ecological influences on hindlimb bone proportions and their relation to prey preferences

Abstract In Strigiformes, which comprise the Tytonidae and Strigidae families, hindlimbs play a crucial role in prey capture. Yet, their bone proportions remain understudied despite the established link between avian hindlimb skeletal morphology and ecological traits. We examined the proportions of the femur, tibiotarsus, and tarsometatarsus in 18 owl species, investigating their associations with prey preferences, body mass, and phylogenetic signals. Our results indicate that owls generally have a short femur and tarsometatarsus, and a relatively long tibiotarsus, all exhibiting isometric scaling relative to body mass. Although evolutionary inheritance influences bone proportions, ecological influences become apparent when the three bones are considered together, highlighting adaptations associated with dietary demands. For instance, the long tarsometatarsus in barn owls facilitates swift movement in dense environments, aiding in the capture of small rodents; whereas in burrowing owls, it enhances terrestrial locomotion. The remaining species exhibited a relatively short tarsometatarsus, which enhances strength and responds to various biological demands, enabling the capture of different prey types and sizes, or improving stability during perching. Our findings suggest that Tytonidae and Strigidae diverged in dietary preferences early in their evolution, with Tytonidae specializing on small rodents and Strigidae evolving from insectivory to more generalized or mammals-based diets.