DISSERTATION RESEARCH: Ecophysiology of Hummingbirds Along an Altitudinal Gradient: An Integrative Approach

点击翻译按钮获取中文摘要

North American hummingbirds are specialized to feed on the energy-rich diet provided by flower nectar. These diminutive birds gain access to flowers through their unique form of locomotion: hovering flight. Hummingbirds are typically found in all North American habitats with abundant flowers,including very high altitude meadows such as those that occur in the Colorado Rocky Mountains. The rufous and broad-tailed hummingbirds compete for floral resources in the Rockies across a altitudinal range spanning 2500 meters. The two species weigh about the same but the wings of the rufous hummingbird are on average only 83% of the size of the broad-tailed hummingbird's wings. Because air is thinner in the mountains, species with large wings can more easily generate enough lift to fly at high altitudes. However, species with larger wings are at a disadvantage at low altitudes because they are less agile than species with small wings. Small-winged species outcompete large-winged hummingbirds at low altitudes, so there is a trade-off between competitive ability and altitudinal range. The PIs predict that rufous hummingbirds will outcompete broad-tailed hummingbirds at low elevations and thus dominate the best resources. Conversely, the rufous will be less competitive at high elevations due to high costs of flight and thus relegated to the less preferred resources. The PIs also predict that the increased costs of flight and related competitive behavior will be influenced by the density of the air rather than by oxygen availability.