CAREER: Hummingbird bill performance while feeding on and fighting for flowers

About This Grant

To survive, animals must access food efficiently and, in some cases, they must fight for it. Adaptations that enhance food consumption or allow species to specialize on different resources—and therefore coexist—have been well-studied, improving our understanding of evolutionary and diversification processes. In comparison, there has been much less research regarding adaptations to defend food, especially in feeding structures. For instance, beak shape in birds has been linked to the demands of exploiting resources; hummingbirds, with their long, thin beaks suited for unique flowers, are a textbook example. Both across species, and even when comparing male to female beaks, the consensus is that the different beak shapes have evolved to better match the shapes of the flowers that the birds visit. Yet hummingbirds also fight over these resources, utilizing their beaks to stab or pluck feathers from opponents. This study investigates aggressive interactions (a previously underexplored evolutionary force shaping hummingbird beaks) and biomechanical performance in puncture, gripping, and fluid transfer, testing the hypothesis that beak shape is not only linked to matching flowers, but also determined by the use of beaks as weapons. In tandem, this project will foster new tools for public engagement and literacy in evolutionary topics of adaptive tradeoffs (e.g., a beak better fit for fighting might be worse at feeding), through a museum exhibit and development of curriculum for middle schoolers, centered around a game wherein students play as different hummingbirds and experience life with their adaptations. This research program provides lasting, transformative mentorship and interdisciplinary training to undergraduates, graduates, and postdoctoral professionals. Linking biomechanics to the ecological determinants of performance and species interactions is vital to grasp the processes shaping organismal evolution. This project challenges the status quo regarding bill-flower coevolution being the sole driver of hummingbird bill variation, to more fully consider the use of bills as weapons as a selective force shaping bill morphology and behavior. In opposition to the existing consensus that resource partitioning is the cause of dimorphism between male and female hummingbird bills, this study tests the hypothesis that differences in bill traits result from tradeoffs between nectar-feeding efficiency and performance in battles among males competing for territories and mates. This project leverages advances in high-speed videography, 3D reconstructions, geometric morphometrics, finite element modeling, and radio-based identification and tracking to assess multiple metrics of performance across organismal scales in both natural and laboratory settings. Finally, this research establishes a novel system to study the evolution of animal weaponry on feeding structures, with directly measurable tradeoffs, and constrained by extreme specialization. Detecting tradeoffs in hummingbird bill form and function will help reshape paradigms regarding hummingbird energetics, and guide research on other selective pressures involved in the evolution of these traits. Failing to detect tradeoffs would be equally compelling: if bill weaponization does not hinder nectar extraction, it would suggest alternative evolutionary workarounds and associated costs. This mechanistic approach to understanding the links between morphology, performance, behavior, and ecology, plus their evolutionary implications, will advance the emerging and interdisciplinary fields of ecophysics and mechanoethology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.