Bursera fruit traits as drivers of fruit removal by flycatchers

Fruit size and shape are key traits that affect the interactions between plants and their seed dispersers within communities. Yet, the co-adaptive morphological links between fruits and bird seed dispersers within highly biodiverse Neotropical dry forests are still poorly understood. In this study, we evaluated the relationship between the morphometric fruit traits of Bursera, a group of dominant trees in tropical dry forests, and the morphometric body traits of flycatcher birds of the Tyrannidae family, their main seed dispersers. We found that the largest bird species primarily consumed large- and medium-sized fruits, while smaller birds targeted plants with small- and medium-sized fruits. Migratory flycatchers were the core species involved in Bursera fruit removal, except in Bursera species fruiting during the rainy season, when these birds are not present. Also, small-sized fruits with an oblong shape tended to be removed more frequently by small-sized birds, while large-oblong fruits tended to be more consumed by larger birds. According to body traits, bill width, tarsus, and wing length had significant effects on fruit removal. Wider-billed Tyrannus, Myiarchus, and Myiodynastes species removed almost half of the fruits. The Myiarchus genus showed the longest tarsus and removed up to 58% of all fruits. The Tyrannus species, which rely on flight to obtain food, showed the greatest wing length. Our findings suggest that morphological traits of Bursera fruits such as shape and size may be fitted to interact with the body traits of their bird dispersers. Studies on seasonally dynamic bird-plant interactions are crucial for a better understanding of the ecological and evolutionary drivers in Neotropical dry forests.