Under Pressure: The Behavioral Richness of Hummingbirds in Competitive Landscapes

Abstract

Competition for resources is a unifying struggle across the animal kingdom. Hummingbirds, facing fierce races for nectar while balancing record-high metabolic demands, are an exceptional case study for this conundrum, and the decisions that these tiny birds must make to survive each day are complex. Where to travel, and which rival is worth attacking? Does it pay off to stay near home, saving energy for inevitable battle, or to fly further afield—facing new perils—to find food? With new approaches and miniature biologgers, we can get a glimpse into how each individual hummingbird might approach these challenges, even and especially when surrounded on all sides by competitors. I have three chapters in my dissertation dedicated to this concept: (1) A published review of the principal strategies with which hummingbirds commute within landscapes (“traplining”) or monopolize flowers (“territoriality”) when competing for finite resources, and the flexibility with which they adapt their behavior while doing so. This review also offers predictions regarding the traits we expect to be associated with these main strategies, along with proposed methods of testing them. (2) An ethical study of how hummingbirds behave when equipped with backpack-style biologgers, in order to ensure that the radio-trackers—which we would use to study hummingbird movement and foraging strategies in the wild—do not drastically alter the very behaviors we would hope to measure in the first place. This chapter was based on a time-budget experiment in which each bird underwent both a tagged and an untagged treatment; we found that birds spent significantly more time preening when tagged. (3) A case study showcasing how differently six tagged hummingbird species can utilize an array of feeders while coexisting under increasingly competitive conditions at an agricultural-forested site in Colombia. In this experiment, we progressively removed and reinstated feeders equipped with radio-frequency identification (RFID) antennas and found that, as scarcity mounted and the birds were funneled onto fewer and fewer options, individuals and species that had little time at the feeders to begin with were more likely to cease visiting them entirely. Overall, my dissertation offers an integrative perspective with which to examine hummingbird foraging and its mutability to the surrounding energetic, risk, and competitive landscapes, accounting for not only morphology and biomechanics, but also the effects of the tools that we use to investigate these strategies, as well as the unique behavioral signature of each individual hummingbird in question.