Global distribution range of birds is negatively correlated with their level of diet specialization

Aim Understanding the factors determining the size of a species distribution range is crucial to preventing the extinction of vulnerable species, particularly specialist species. Previous research has shown that climate and various traits of a species significantly affect its distribution range size. However, the impact of avian dietary specialization remains relatively unexplored and geographically restricted. Location Worldwide. Taxon Birds. Methods We assessed the worldwide distribution range of 7416 bird species concerning the degree of diet specialization, including body mass size, daily activity and evolutionary distinctiveness (ED) as covariates. The phylogenetic generalized least squares (PGLS) model – including the avian phylogeny – was used to test the potential correlation between the distribution range size of bird species and the explored life history traits. Results We found that, at a global scale, diet specialization negatively correlates with the distribution range size of bird species. Overall, diet specialist species displayed a distribution range of 60% smaller than generalist species. Main Conclusions Our study demonstrates that an avian diet specialization is crucial in predicting its potential distribution range size. This information is essential for those species with narrow distribution ranges often threatened by global concerns.