Meeting Abstract
Hummingbirds are ecologically important because they are pollinators for many nectar-producing plants. Climate change threatens the link between hummingbirds and plants in many ecosystems because of the sensitivity of both hummingbirds and plants to higher environmental temperatures. How hummingbirds physiologically respond to higher temperature is virtually unknown. We present data for broad-billed hummingbirds (3.2g; Cynanthus latirostris) from a cooler, protected habitat (HC) compared to an exposed, warmer habitat (SC) to illustrate how high temperature impacts daily energy expenditure (DEE) and energy-budget management. In both habitats DEE in June, when peak temperature was 45-50°C, was 28% lower than in July when monsoons routinely reduced peak temperatures to <40°C. The reduced DEE is due primarily to reduced thermoregulatory costs. DEE was always 15-20% higher at SC where temperature was 5°C warmer for much of the day. In both habitats birds appeared to behaviorally regulate plumage surface temperature when temperatures were within 3°C of body temperature to avoid absorbing heat. Nighttime temperature was 10°C warmer at SC were birds spent 66% less time in torpor and had 20% higher nighttime energy costs. However, nighttime energy costs accounted for only 25% of the higher DEE at SC. The remaining difference in DEE could be due to behavioral changes related to structural differences between sites. Our data suggest that higher temperatures related to climate change will not push broad-billed hummingbirds beyond their physiological tolerance as long as their habitat structure remains intact.
