Meeting Abstract
During hovering hummingbirds generate large amounts of heat that must be dissipated to maintain normal body temperature. Hummingbirds have two physiological methods of dissipating heat, evaporative and passive heat loss. These methods appear to be insufficient when hummingbirds hover at ambient temperatures >35 °C likely requiring behavioral cooling while perching between hovering bouts. We predict that during warm parts of the day hummingbirds will select perching locations in cooler microclimates that 1) provide thermal gradients suitable for passive heat loss and 2) are relatively close to a food source to minimize hovering distance. We conducted this study in the Chiricahua Mountains of SE Arizona during summer 2019. We recorded perching locations, frequency of perch use and feeding, and feeding bout duration in black-chinned (Archilocus alexandri) and Rivoli’s (Eugenes fulgens) hummingbirds, and blue-throated mountain-gems (Lampornis clemenciae). Ambient and operative temperatures of the study site as well as ambient temperature of common perching microclimates were recorded to characterize potential thermal gradients. Daytime operative temperatures ranged from 16°-46°C, which includes extended periods where passive heat dissipation is not possible. Hummingbirds used perches where ambient temperature was <35°C 2X more frequently than perches with higher ambient temperatures throughout the day. Perches in close proximity (within 2 m) to feeders were used frequently in the morning, but often experienced midday ambient temperatures >35 °C at which point they were largely abandoned. These data are consistent with the notion that hummingbirds select perches that support passive thermoregulation. Both perch microclimate and location appear important, but microclimate appears most important when operative temperature is >35°C.
