Responses of Broad-tailed Hummingbird Foraging Behavior to Climate Change Across Multiple Temporal Scales

Abstract

As climate change causes the timing of flower bloom and pollinator activity to shift at different rates, mutualisms between plants and their pollinators are at risk of temporal mismatch. In the case of the Broad-tailed hummingbird (Selasphorus platycercus), a migratory hummingbird that spends its summer breeding seasons in the western United States, dates of floral bloom at the northern end of its breeding range have advanced faster than the date of hummingbird arrival, which may compress hummingbirds’ breeding periods and reshape the plant-pollinator networks in which they participate. In this study, I sought to characterize hummingbird floral visitation patterns on the scale of years, weeks, and times of day and determine how climate change may affect these patterns in the future. I analyzed time-lapse camera footage of hummingbird visitation to flowers collected in Gothic, Colorado across two consecutive years, in which flowering took place much earlier in one than in the other. I predicted that in the year of earlier flowering, mirroring the predicted effects of climate change, hummingbirds would experience lower floral availability and would adjust their foraging patterns to compensate for the limited resources. Contrary to my expectations, I found that in the year of very late snowmelt, hummingbirds were less choosy with floral resources and extended their daily foraging periods, indicative of resource limitation. I also found that networks of hummingbird-plant interactions varied greatly between and within years, and that diel patterns in hummingbird foraging vary depending on flower species and environmental conditions. This study highlights the flexibility of hummingbird foraging behavior in the face of environmental variation and points to the utility of long-term camera trap studies of plant-pollinator interactions as a way to characterize these networks and predict their responses to climate change.