Updated: Nov 24, 2020
Winter is HERE! The incredible adaptations of birds to harsh climates are almost endless. In fact, the answer to this question will only make you appreciate birds even more!
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Do birds hibernate?
No, birds do not hibernate in the 'traditional' way. What do they do? They use a strategy called torpor, explained in the next section. When we think of traditional hibernation, many of us think of bears crawling into a cave to sleep for the winter. However, 'hibernation' is much more complex and diverse than how we perceive a bear's extended sleep. What is traditional hibernation? It is defined in animals as having a reduced metabolic rate and body temperature near the ambient temperature over prolonged times in the winter. The summer version of hibernation is estivation. Instead of using hibernation or estivation, some birds use a unique strategy known as torpor.
Many types of animals enter a reduced state of temperature, activity, or energy use for many different reasons. Birds are no different. From cold temperatures to low-food availability, birds do need to enter into a special state to survive harsh conditions.
*Note: The Common Poorwill enters into prolonged deep torpor that highly simulates 'traditional' hibernation. Could it be technically defined as hibernation? Yes.
What is torpor?
The definition of torpor, which is technically known as temporal heterothermy, is: a strategy used by birds allowing their core body temperature to drop when needed, usually as a response to external stimuli. What the phalarope does that mean? It means certain species of birds can respond to adverse weather and food-availability by decreasing their metabolism and body temperature. Need more simplification? 'Bad weather and no food mean bird get sleepy.' I literally cannot make it easier to understand.
Torpor and hibernation are intricately tied together, as extended torpor over the winter season, is hibernation. This is often where the confusion exists. If you use the terms loosely, fear not, the grammar police have no actual authority over you.
Which bird species go into torpor?
Likely, a wide variety of birds can enter into a torpor-like state. However, the species most known for their incredible torpor abilities are the goatsuckers (poorwills, nighthawks, oilbirds) and hummingbirds. Larger species are less likely to enter into a true torpor state, as the length of time required to bring their internal temperatures back to its normal state. Outside of the goatsuckers and hummingbirds, what other species enter into a torpid state? The Greater Roadrunner of the desert southwest will enter into a shallow torpor during the winter months. Why? Some of its main prey items, like lizards and snakes, go into hibernation decreasing their availability to the Greater Roadrunners. There are also several types of birds in the tropics that use a shallow torpor during the cooler rainy season, such as manakins.
Which of these species has the most impressive bouts of torpor? I guess that depends on your opinion of impressive. The Common Poorwill, for instance, can remain completely inactive for as much as 94% of the winter season, in the southern extent of the range. Scientists have recorded body temperatures as low as 41°F (5°C) with oxygen consumption reduced by over 90%! The longest documented torpor state in a Common Poorwill is reportedly 25 consecutive days. Wow!
A recent study from the Andes Mountains of South America recorded a hummingbird, the Black Metaltail, as decreasing its body temperature to as low as 37.9°F (3.3°C). This is a new record, for the lowest controlled body temperature decrease in birds! How impressive is this? These hummingbirds were decreasing their body temperatures by over 86°F (30°C). BOOM. If you still cannot grasp how impressive that is, imagine a typical, healthy human. If a healthy human's core temperature drops by approximately 36°F (2°C), they will become hypothermic. However, this 6-gram bird can accomplish this task in half an hour. Birds are amazing. Do not forget it.
So kids, when your parents tell you to put on a jacket, just do it. You are no metaltail.