The effect of nectar concentration on foraging strategies among hummingbirds (Aves: Trochilidae) at artificial feeders

Abstract

Hummingbirds are specialized nectarivores and their feeding behavior at artificial feeders is highly variable. Not all hummingbirds select their food in the same way, hence there are preferences for the consumption of specific resources. In this study, foraging patterns around feeders were evaluated in a hummingbird assemblage at the Colibrí Gorriazul Research Center. We recorded high-speed videos in a three-replicate experiment analyzing hummingbirds’ visits to syringes modified as feeders with varying nectar concentrations at five daily time intervals, four days a month, for four months. We quantified nectar consumption, the number of feeding bouts, the number of visits and visit duration. Additionally, we compared data from visits with and without competitors. We found that hummingbirds performed visits of long duration and a low number of feeding bouts. When competitors were present, the foraging pattern was altered, increasing both the visit duration and the number of feeding bouts. Nectar consumption and the number of visits were lower in feeders with extremely low/high concentrations, and these values increased in intermediate concentrations, especially at 20% concentration (which is commonly found in ornithophilous flowers). Foraging patterns differed among species, smaller ones performed shorter visits and fewer feeding bouts than larger species. In the instances in which we inferred the sex of individuals based on plumage dichromatism, males visited the experimental setup more frequently than females, in the absence of competitors. The abovementioned foraging variables were not correlated to the time of day, but nectar consumption varied considerably among the months studied. These results allow us to observe in detail, with almost 3000 records, hummingbird foraging strategies in modified environments, analyzing resource quality (varied nectar concentrations), and including competition. Future studies should complement these results with the evaluation of other factors (individual-level data, floral anatomy, resource location) known to modulate foraging behavior.