Are perches on humming bird feeders bad for the humming birds?

Question

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?

Answer 1

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.

Answer 2

Published research shows that hypothermia is not at all the same as torpor in hummingbirds. Sleeping is an entirely different condition than either. If the hummingbirds sit on feeder perches to ingest cold sugar water and then fall or try to fly and in either case end up on the ground, they are in grave danger from predators.

In addition, female birds can't return to their nests to keep eggs and hatchling warm, so the entire family is lost if the mother bird becomes hypothermic from feeding while motionless on a feeder perch.

Even if they sit unresponsive on or hang from feeder perches, they are in danger of dying because the condition is hypothermia and the birds that are completely unresponsive because of hypothermia are said by researchers who are experts in hummingbird thermodynamics to be close to death. If the temperatures are cold in the morning or any time during the day, only feeders without perches should be used to keep from killing the birds you are trying to help.

Thank you for taking off the perches or only using perchless feeders if temperatures are below 60 degrees where you live.

The reference for the study that showed that torpor and hypothermia are two completely different conditions is Torpor and hypothermia: reversed hysteresis of metabolic rate and body temperature Fritz Geiser, Shannon E. Currie, Kelly A. O’Shea, and Sara M. Hiebert.
Am J Physiol Regul Integr Comp Physiol 307: R1324–R1329, 2014. First published September 24, 2014; doi:10.1152/ajpregu.00214.2014.

Just being asleep for a hummingbird is not the same condition as torpor or as hypothermia, so sleeping is a third condition.

This study showed that the hummingbirds in the study under controlled conditions with everything measured had their wing muscles adversely affected so they could not fly as well after drinking cold sugar water while remaining motionless on a perch.

Flight Thermogenesis And Energy Conservation In Hovering Hummingbirds PENG CHAI1, ANDREW C. CHANG1 AND ROBERT DUDLEY The Journal of Experimental Biology 201, 963–968 (1998) Printed in Great Britain © The Company of Biologists Limited 1998 JEB1196 963

With some species of hummingbird in serious decline, everything possible should be done to keep them safe from harm.