Energetically constrained animals have evolved adaptations to enhance caloric intake. On the other hand, animal competition sometimes turns into physical combat, and particular weaponry evolves. I perform theoretical and empirical research on each of these fronts, and study an unexpected case of their intersection: hummingbird bill weapons. My recent discoveries revive questions dating back to Darwin and Wallace about how these birds budget energy gain and expenditure to enable hovering, the most expensive form of locomotion, establishing coevolutionary relationships with flowers, and a peculiar adaptive radiation. These novel perspectives of a data-rich mutualistic system, open the door to quantitative and comparative assessments of trade-offs between energy optimality and fighting proficiency. I translate the insights from this work into testable hypotheses for a plethora of nectar-feeding animals, and the evolution and constraints of the evolution of combat traits in nature. My research is question-, rather than technique-driven; thus, I pursue cross-disciplinary approaches aimed to achieve a more complete integration across biological levels of organization.