How Do Birds Cope With Winter Temperatures? 

By Greg Martin

Liberty Wildlife Volunteer

[Article originally published in January 2011 Nature News]

How do birds cope with winter temperatures? It’s a simple question with very complex answers. Many species migrate immense distances, en masse, in an attempt to circumvent dropping temperatures by traveling to more mild climates until spring. Then, they’ll head back to their original homes to enjoy a comparatively gentle summer. But how do they do it?

Swainson’s hawks travel from western North America to the pampas of Argentina every winter, a journey made by hundreds of thousands of hawks traveling in gigantic flocks. This 6,000-mile journey gives them the best of both worlds – a comfortable home in the pampas from which to avoid harsh temperatures in Canada and parts of the U.S., while their spring return to North America promises temperate conditions in which to raise their young.

Birds that migrate as a response to changing temperatures do so with the benefit of some truly remarkable evolutionary adaptations. Migratory birds generally have larger pectoral muscles, which enable them to burn calories for energy at a more efficient rate than non-migratory species. These muscles have been shown to actually increase in size just prior to the migration, to further aid the birds in breaking down fat to energy. Additionally, migratory birds enter into a “feeding frenzy” in the weeks prior to migration, a period accompanied by a proportional increase in body mass. This gorging process allows them to build up the fat reserves necessary to fuel themselves on their long flight.

A perfect example, the Pacific golden plover, migrates from some of the coldest places on earth, like Siberia and Alaska, to spend its winters in Hawaii and on other Pacific islands. This journey, over 4,000 miles one way, is impressive by itself, but the golden plover does this without stopping, through a period of continuous flight over deep ocean that can last one hundred hours or more.

These physiological changes allow birds to undertake journeys of thousands of miles, often over open ocean, as in the case of the golden plover, where places to rest or eat are few and far between. Birds that cross oceans on their migratory path have developed responses to their basic biological needs in order to keep themselves going. The artic tern, which makes a yearly round-trip of nearly 20,000 miles – from the Arctic where it breeds, down to the Antarctic, and back – is capable of feeding while at sea, enabling it to provide for itself even on such an incredible odyssey.

As impressive as avian migration is, one of the most unassuming birds has developed a technique that, while not necessarily a substitute for migratory flight, allows them to cope with cold temperatures that would otherwise be fatal to their wonderfully unique design. Hummingbirds possess an incredibly fast metabolism and a body temperature that normally rests at 105 degrees, and while some, like the ruby-throated hummingbird, do migrate, they are uniquely vulnerable to temperate shifts because of their internal workings. Their response is something called torpor, an occurrence where their body temperatures decrease, almost to the point of hypothermia. This is essentially a short-term occurrence of what, over longer periods, would be called hibernation. By going into torpor whenever necessary, they can survive sudden drops in temperature or moments when there isn’t enough food to keep their internal furnaces going at full speed.