Why Some Birds Dont Migrate

Flying south to escape cold northern winters
is a luxury for the birds, right? Not always. Hey guys, Amy here with DNews, and as you
suffer through the dregs of a ridiculously cold winter youre not alone. Some species
of birds are right there with you, but without the benefit of indoor heating and wool sweaters.
So how exactly do small animals survive harsh winters? Whether or not a given bird species flies
south for the winter depends a lot on what its diet is. If a bird exists largely on flying
insects and nectar it will likely migrate south during the cold seasons since these
food sources arent exactly plentiful in cold weather.

But if a bird lives off seeds
or insects that live under tree bark, it can usually find enough food to spend the winters
in the north, even if the temperatures drop dramatically. But having food doesnt equal warmth. Small
animals have a large surface area compared to their body size. They also cant store
as much fat so they have less insulation.

All this means they are more prone to losing
heat once the cold sets in, and surviving a cold winter is all about preventing heat
loss. Biologists at the Norwegian University of
Science and Technology did some research on the survival skills of these non-migrating
birds and found some interesting things. For instance, some species survive by using the
snow to their advantage. Like the small hazel grouse or hazel hen common in Northern Europe
as well as small rodents like voles and field mice.

These small animals burrow into the
snow, digging out little tunnels to sleep in at night or rest in during the day. The
snows insulting properties mean these animals can focus on finding food and not on surviving
cold nights. For some species, strength comes in numbers.
One of Norways smallest birds, the Eurasian wren, spends cold nights huddled together
under the snow. They can congregate into groups of as many as 60 birds, huddling in layers
to share and conserve vital body heat.

But its not the case that all species make
their own nests to fight off the cold. Some species of tits just take over existing nests,
often fighting over the best sleeping spots at twilight. And some birds have a completely different
way of dealing with the cold: they can actually slow their metabolism and lower their core
temperature to reduce body heat loss. Like willow tits.

These tiny birds can reduce their
body temperature from about 105 to 87 degrees Fahrenheit. They have a finely tuned internal
thermostat that tells the bird to start shivering when its core temperature reaches about 90
degrees. Just the act of shivering produces enough heat to allow the bird to stabilize
its core temperature. Arent you glad you dont have to tough
it out outside all winter? But if you ever have spent a recreation night out in the cold,
how did you stay warm? Let us know in the comments below or you can
let me know directly on Twitter as @astVintageSpace.

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