Meeting Abstract
Faced with increasing temperatures due to climate change, researchers are looking to small, temperature-sensitive organisms such as hummingbirds to help understand how these changes will alter ecosystems and impact biodiversity. In response to increasing temperatures, these organisms may travel to higher elevations to escape thermal stress. At high elevations, however, lower air density can decrease convective-conductive heat transfer, and increase exposure to solar radiation. In this study we assess whether increased intensity of solar radiation at high elevations results in higher thermal loads for hummingbirds in spite of lower environmental temperatures. To test this we used infrared thermography to measure surface temperature (Ts) in free-living hummingbirds at mid-elevation (1500-1900m) and high-elevation (~3000m) sites in SE Arizona to measure the impact on radiant load. We found a strong linear relationship between hummingbird Ts and environmental temperature at both our mid and high elevation sites. At mid elevation, Ts changed 0.5-0.8 °C/°C Ta depending on species and, in some cases, gender. At high elevation, Ts changed <0.3 °C/°C Ta. Lower environmental temperatures at high elevations may affect thermal gradients in such a way that convective-conductive heat loss from a hummingbird’s surface far surpasses any increase in radiant heat gain. Additionally, both high mid elevation sites offered dense vegetation that likely enabled hummingbirds to avoid exposure to direct solar radiation. These data suggest that vegetative structure will play an important role in the ability of hummingbirds to tolerate increased environmental temperature due to climate change.
