Apparently, there is a theory that says

Hummingbirds can become hypothermic if they sit on a feeder perch and drink several cropfuls of cold sugar water early in the morning. The birds fall to the ground unresponsive if they become extremely hypothermic. If they are not found before they die and warmed up, they just lay on the ground or in one case on the chair until they die.

My experience says that sometimes they hover and sometimes they sit, it just depends on the hummingbird and how many of them are at the feeder at once.

Is there any evidence to back this theory up?

  • Perhaps those slipping into hypothermia are more likely to sit? – Jon Custer May 8 '19 at 0:18

This is not supported.

Hummingbirds have a very high metabolic rate, the highest rate among all tetrapods (all the land dwelling animals). They do appear to sometimes fall over after drinking the sugar water, but that is likely because it is super cold and remains liquid below freezing and so the poor bird gets a bit of shock when it realizes that the nectar is way colder than they expect.

Given that they are known to go into a torpor on many nights (a very deep sleep where they drop their body temperature to conserve energy), the shock from the cold sugar water likely does not harm it too much, as their bodies can handle dropping considerably in temperature. My guess is that the hummingbirds that have been cited as being influenced by the presence of a perch simply dropped into a torpor suddenly and were fine after they rested.

Having a perch is not going to harm these hummingbirds. They are capable of either hovering or perching, but perching is simply easier for them and is likely helpful in the early morning when they just exited torpor and their energy storage is low.

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