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

北美蜂鸟专门以花蜜提供的富含能量的食物为食。这些小型鸟类通过它们独特的运动方式——悬停飞行——获得了接近花朵的机会。蜂鸟通常出现在北美所有有繁花的栖息地，包括高海拔的草甸，比如科罗拉多落基山脉。红褐色和宽尾蜂鸟在海拔2500米的落基山脉上争夺植物资源。这两个物种的重量差不多，但红褐色蜂鸟的翅膀平均只有宽尾蜂鸟翅膀的83%。由于山区空气稀薄，有大翅膀的物种更容易产生足够的升力在高空飞行。然而，翅膀较大的物种在低海拔地区处于不利地位，因为它们不如翅膀较小的物种灵活。在低海拔地区，小翼蜂鸟比大翼蜂鸟更有竞争力，因此在竞争能力和海拔范围之间存在着一种权衡。PIs预测，红褐色蜂鸟将在低海拔地区与宽尾蜂鸟竞争，从而占据最佳资源。相反，由于飞行费用高，红豆在高海拔地区的竞争力较弱，因此被降级为不太受欢迎的资源。pi还预测，飞行成本的增加和相关的竞争行为将受到空气密度的影响，而不是氧气供应的影响。

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.