About This Project

When hummingbirds hover they generate heat that must be lost to avoid overheating. At high temperatures, heat is eliminated is by evaporation. Previous work suggests that during hovering plumage might restrict evaporative heat loss. We will use a novel method to measure total evaporation in free-living hummingbirds. This work is important because hummingbirds are key pollinators that need to be active even at high temperature.

Ask the Scientists

What is the context of this research?

Hovering is vital to hummingbird foraging and pollination activity. At high temperatures (>36°C), heat can only be lost by evaporation. Evaporation occurs via respiration and across the skin (cutaneous). Earlier work suggests respiratory evaporation can dissipate <40% of heat produced during hovering. Thus, cutaneous evaporation is needed to compensate for extra heat produced. Cutaneous evaporation appears easily increased in resting birds, but preliminary data suggests that the aerodynamic form of plumage during hovering might restrict cutaneous evaporation. We propose to measure total evaporative heat dissipation over a range of temperatures to measure its ability to dissipate heat produced during hovering.

What is the significance of this project?

Mean global temperatures have risen every decade since 1970. In response, current climate models predict increasing extreme heats and are projected to adversely affect ecosystems, including ones where hummingbirds are major pollinators. This could prove challenging for hummingbirds. Studies suggest that some hummingbird climates are already sufficiently warm during the day to require evaporation to regulate body temperature. Because hummingbirds are key pollinators, their inability to function (hover) in ecosystems could reduce plant reproduction and ecosystem biodiversity. Additionally, hummingbirds are key indicator species and understanding how hummingbirds manage body temperature during these challenges will be valuable for planning ecosystem management strategies.

What are the goals of the project?

The primary goals of this project are:

1) To measure the ability of free-living hummingbirds to lose extra heat produced during hovering by evaporation when temperatures are high (>36 °C). We will do this using a novel method that has proven accurate in measuring respiratory evaporation in previous studies. We predict that during hovering the plumage will restrict evaporation.

2) To determine if hummingbirds increase nectar intake, and thus water intake, when temperature is high to support increased evaporation. Since hummingbird nectars are primarily water, we predict that when environmental temperature is high that hummingbirds will abandon their typical pattern of mass management and increase water consumption to support higher evaporation.