Antipredator behaviors of ruby-throated hummingbirds: Are bees a threat?
Despite few specialist predators and a relatively low apparent risk of predation, hummingbirds have been shown to exhibit changes in antipredator vigilance that mirrors the well-studied antipredator vigilance trade-offs in other species of birds. Due to their high metabolic rates, greater vigilance in high-risk conditions may be associated with significant energetic costs. In addition, small body mass makes hummingbirds susceptible to opportunistic predation by a variety of taxa, including insects. Some potentially dangerous insects (including eastern yellow-jackets, Vespula maculifrons) have even been observed pursuing hummingbirds away from shared high-sugar food sources. Thus, although little is known regarding the types of factors that hummingbirds perceive as dangerous, it is likely that hummingbirds frequently encounter high-risk foraging conditions. The goal of this study was to examine the antipredator behaviors of ruby-throated hummingbirds (Archilochus colubris) under different levels of perceived risk. To accomplish this goal, free-ranging birds were observed while feeding at visually obstructed or unobstructed sugar-water feeders under the naturally occurring presence or absence of yellow jackets on the feeder.
Ruby-throated hummingbirds probed in-and-out more frequently when feeding from visually obstructed feeders, suggesting that hummingbirds are more vigilant when they do not have a clear view of their surroundings. Hummingbirds also appear to perceive yellow jackets as a threat; hummingbirds probed more often when bees were present, regardless of whether the feeder was visually obstructed or unobstructed. Additionally, hummingbirds avoided bee-infested feeders and were often observed being chased away from feeders by yellow jackets. These antipredator behaviors disrupt normal feeding patterns and may lead to significant energy costs. Thus, although bees do not likely pose an immediate survival risk, the threat associated with these insects may have wide-reaching ecological and physiological impacts on hummingbirds.