Foraging Behavior of Broad-Tailed Hummingbirds in the Rocky Mountains: Sex Differences, Floral Abundance, and Visual Ecology

Abstract

Broad-tailed hummingbirds (Selasphorus platycercus) are important migratory pollinators in Rocky Mountain wildflower communities. Climate change will cause shifts in environmental cues that could drive phenological mismatch between the arrival of these pollinators and the blooming of key flower species. An understanding of the impacts of phenological mismatch requires a more thorough characterization of broad-tailed hummingbird foraging behavior. In this paper, I explored sex differences in visitation patterns, the influence of floral abundance on the timing of foraging, and the role of flower color in shaping hummingbird preferences. I analyzed data from a five-year camera trapping project at the Rocky Mountain Biological Laboratory (RMBL) and began collecting floral abundance and reflectance data during the field season. Adult male birds visited atypical hummingbird flowers more often than females and juveniles, highlighting the importance of a diversity of flower species. Different plant species also showed variability in the seasonal synchronization of floral density and hummingbird visit rate. For the two most visited flower species, visit rate did not directly correlate to floral density, indicating a distinct floral preference different from random chance. Visual modeling in tetrahedral color space suggested no strong separation between the flowers visited by hummingbirds and those not visited by hummingbirds. However, the most frequently visited flowers primarily stimulated the long-wavelength-sensitive cone. Overall, these results highlight the complexity of hummingbird–plant dynamics, with sex and flower species influencing the rate and timing of visits in nuanced ways.