Morphometric insights into fly-and-forage evolution and systematics of Asio (Strigiformes: Strigidae)

Abstract Although Asio species exhibit marked variation in fly-and-forage strategies, no studies have examined the evolutionary morphological adaptations of these behaviors, and their taxonomic implications. Thus, we performed morphometric analyses of 12 postcranial skeletal elements across five Asio species to address the evolution of fly-and-forage behavior and taxonomy. Principal Component Analysis explained 94% of the variance, while Cluster Analysis produced a high correlation coefficient (0.8497), consistently grouping species into two clusters: A. flammeus/A. capensis/A. otus and A. clamator/A. stygius . This arrangement corroborates molecular and morphological phylogenetic hypotheses, except for A. otus . Clustering of A. capensis/A. flammeus , and A. otus is plausibly explained as the independent acquisition (convergent evolution) of postcranial skeletal morphology associated with long-distance migration, gliding flight mechanics, and similar trophic specializations. Conversely, A. stygius and A. clamator exhibit strong morphological similarity, consistent with their shared ecology as non-migratory owls inhabiting analogous Neotropical environments and displaying comparable foraging behaviors. Ancestral state reconstruction indicates gliding flight and migratory behavior represent derived traits evolving secondarily within Asio , rather than ancestral conditions. Additionally, South American Asio flammeus suinda clusters more closely with A. clamator and A. stygius than with Old World populations of A. flammeus or with A. capensis . This pattern highlights pronounced intraspecific variation in skeletal morphology within A. flammeus and underscores the need for renewed taxonomic scrutiny of both A. flammeus and A. clamator complexes. These owls are widely distributed, with disjunct ranges and numerous described subspecies adapted to diverse ecological conditions, raising the possibility that each may comprise multiple species.