Beak height and nest structure shape avian bite force.

Bite force is a key performance trait in vertebrates, affecting prey capture, defense, resource competition, and other ecologically important behaviors. Despite broad functional relevance, systematic studies on avian bite force remain limited across species, and the morphological indicators used to infer bite performance are often inconsistent. The evolutionary mechanisms proposed to shape bite force, including diet, combat, and nest-complexity hypotheses, also remain insufficiently tested at broad comparative scales. Here, bite force and associated morphological traits were measured across 175 bird species to evaluate anatomical predictors of bite performance. Comparative analyses revealed that beak morphology, particularly beak depth, was more strongly correlated with bite force than cranial shape excluding the beak. To examine macroevolutionary patterns, newly generated measurements were integrated with published data, yielding a dataset of bite force values for 223 species. Phylogenetic generalized least-squares models were then used to assess proposed ecological and behavioral drivers of bite force, including body mass, diet, competition intensity, and nest structure. In addition to the allometric effect of body mass, nest-structure complexity emerged as a significant predictor of bite force, with species that construct more elaborate nests exhibiting stronger bite performance. These findings are consistent with the nest-complexity hypothesis and indicate that nest-building behavior has likely contributed to evolutionary diversification of bite force in birds. This broad comparative analysis clarifies the anatomical basis of avian bite performance and identifies key behavioral factors associated with the evolution of bite force.