Beak shape and nest material use in birds

The evolution of behaviour can both influence, and be influenced by, morphology. Recent advances in methods and data availability have facilitated broad-scale investigations of physical form and behavioural function in many contexts, but the relationship between animal morphology and object manipulation – particularly objects used in construction – remains largely unknown. Here, we employ a new global database of nest materials used by 5,924 species of birds together with phylogenetically-informed random forest models to evaluate the link between beak shape and these nest-building materials. We find that beak morphology, together with species diet and access to materials, can predict nest-material use above chance and with high accuracy (68-97%). Much of this relationship, however, is driven by phylogenetic signal and sampling biases. We therefore conclude that while variation in nest material use is linked with that of beak shape across bird species, much of this relationship is modulated by the ecological context and evolutionary history of these species.