Abstract
Most birds of prey (raptors), rely heavily on their talons for capturing prey. However, the relationship between talon shape and the ability to take prey is poorly understood. In this study we investigate whether raptor talons have evolved primarily in response to adaptive pressures exerted by different dietary demands, or if talon morphology is largely constrained by allometric or phylogenetic factors. We focus on the hallux talon and include 21 species in total varying greatly in body mass and feeding ecology, ranging from active predation on relatively large prey to obligate scavenging. To quantify the variation in talon shape and biomechanical performance within a phylogenetic framework, we combined three dimensional (3D) geometric morphometrics, finite element modelling and phylogenetic comparative methods. Our results indicate that relative prey size plays a key role in shaping the raptorial talon. Species that hunt larger prey are characterised by both distinct talon shape and mechanical performance when compared to species that predate smaller prey, even when accounting for phylogeny. In contrast to previous results of skull-based analysis, allometry had no significant effect. In conclusion, we found that raptor talon evolution has been strongly influenced by relative prey size, but not allometry and, that talon shape and mechanical performance are good indicators of feeding ecology.
Highlights
Identifying the factors that drive morphological evolution is a central topic in evolutionary biology[1,2]
The species included in this study have been classified into the following three broad categories according to the ratio between their average body mass and maximum prey body mass: relatively small to medium sized prey (SM), assigned to species that are able to capture prey that weighs up to half of their body mass; medium to large sized prey (ML), assigned to species that are able to capture prey weighing from half to more than half of their body mass; non-predatory (NP), assigned to species that don’t use their feet for prey capture
Principal Component Analysis (PCA) plots show a clear separation between the three considered dietary categories, i.e., non-predators (NP), and predators on relatively small prey or large prey (SM and ML, respectively) (Fig. 1 and Supplementary Fig. S1)
Summary
Identifying the factors that drive morphological evolution is a central topic in evolutionary biology[1,2]. We combined 3D geometric morphometrics (GMM), Finite Elements Analysis (FEA) and Phylogenetic Comparative Methods (PCM) to provide a deeper understanding of raptor talon evolution These methods can be integrated within the framework of evolutionary biology and their combined application has yielded significant advancements in the understanding of evolutionary dynamics among different clades[15,16,17]. We sampled representatives of each raptorial clade (Accipitridae, Falconidae, Strigiformes and Pandionidae), as well as non-raptorial species (Passeriform, Psittaciform) to determine whether, in a phylogenetic context, the evolution of raptor talon shape and biomechanical performance has been driven by feeding ecology, or whether, as with the avian skull, it has been heavily constrained by allometric factors
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