The evolution of morphological traits is often strongly influenced by functional and biomechanical demands. Perhaps the best example of this is the avian bill, a multifunctional appendage consisting of an inner bony core and an outer keratinous rhamphotheca, which presents a unique opportunity to study form-function relationships. Among the varied functions of the bill, certain groups of birds use their bills to excavate tree hollows for nesting, roosting, and feeding. The physical stresses experienced during this mechanically demanding task may be linked to bill shape and material properties, and also to broader factors like environmental conditions which influence the availability and mechanical properties of the substrate. Here, we examine these relationships in the frugivorous Asian and African barbets, which occupy diverse climatic regimes and excavate nest hollows in trees. Using micro-CT scans of museum specimens coupled with landmark-based geometric morphometrics, we find that bill shape diversity has accumulated gradually over time in both clades under allometric constraints, and exhibits a significant relationship with climatic variables. Secondly, using finite element analysis and beam theoretic approaches, we find that maxillary geometry trades off with excavation performance under different loading regimes. Our study thus aims for an integrative, interdisciplinary understanding of the evolution of morphological traits in birds.

Schools of fish and flocks of birds display an impressive variety of collective movement patterns that emerge from local interactions among group members. These collective phenomena raise a variety of questions about the interactions rules that govern the coordination of individuals’ motions and the emergence of large-scale patterns. While numerous models have been proposed, there is still a strong need for detailed experimental studies to foster the biological understanding of such collective motion phenomena. I will first describe the methods that we developed in the recent years to characterize social interactions between individuals involved in the coordination of swimming in groups of Rummy-nose tetra (Hemigrammus rhodostomus) from data gathered at the individual scale. This species of tropical fish performs burst-and-coast swimming behavior that consists of sudden heading changes combined with brief accelerations followed by quasi-passive, straight decelerations. Our results show that both attraction and alignment behaviors control the reaction of fish to a neighbor. Then I will present how these results can be used to build a model of spontaneous burst-and-coast swimming and social interactions of fish, with all parameters being estimated or directly measured from experiments. This model shows that the simple addition of the pairwise interactions with two neighbors quantitatively reproduces the collective behavior observed in groups of fish. Increasing the number of interacting neighbors does not significantly improve the simulation results. Remarkably, and even without confinement, we find that groups remain cohesive and polarized when each fish interacts with only one of its neighbors: the one that has the strongest contribution to the heading variation of the focal fish, dubbed as the “most influential neighbor". Overall, our results suggest that fish avoid information overload when they move in large groups since individuals only have to acquire a minimal amount of information about the behavior of their neighbors for coordinating their movements.