Physiological Issues of Hummingbird Torpor

Birds, being endothermic animals, expend energy to maintain a stable body temperature. However, any smaller endothermic animal must expend a large amount of energy to maintain its body temperatures constant, due to an increased surface area to volume ratio (McKechnie 2002). This problem, while common among many species of small birds and mammals (Geiser 1995, Zwartjes 1999), is an extremely important issue for hummingbirds. Due to their extremely small size, hummingbirds must expend enormous amounts of energy to maintain a constant body temperature (Hiebert 1991, McKechnie 2002).

Image of E. jugularis property of and provided by NJ Larsen, all copyrights reserved.

Hummingbirds are able to consume enough energy for their daily activity by procuring most of their nutrients from high energy nectar (Bech 1997). However, since hummingbirds need to sleep, they cannot be constantly drinking nectar. This leads to an interesting problem: if hummingbirds are burning enormous quantities of energy to maintain their high body temperature, where will they get the energy necessary to maintain their high body temperature when they cannot eat (i.e., while roosting)?

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