Sunday, March 22, 2015

Surviving that long night of the Northern winter

What's a ptarmigan, you might ask?

That's a ptarmigan (Tar-mi-gan)
photo: Gail Hampshire

No, that's a ptarmigan!  (Same species, different season!)
photo: Dave Menke, USFWS

No, that's a ptarmigan! Same species, different gender (this is a male) 
photo: Dave Menke, USFWS

Actually, the ptarmigan is a lovely bird that lives in the higher northern latitudes and changes its plumage to survive both summer and winter. Males and females look different in summer time, so you all are right.

Ptarmigans don't just change color. Oh no! They also prepare and execute several strategies each year that allow them to thrive in a range of chilly places.

Why so much planning?

Here in the mid-Atlantic US, the birds are chirping and we had temperatures near 68 degrees F (20 C), which is basically shorts weather for anyone from the UK or Canada.

hopeful flower worshipper waiting ready for spring!
Despite the birds' enthusiasm and the warm days last week, we have had a lot of snow and cold here this winter, and it just snowed again 2 days ago, requiring a bit more bird seed to be put out for our feathered friends (all of which gets eaten by this guy...).

Yet cold and snow in Washington, DC is nothing like that fearsome duo in the Far North. Take Norway, for example.

This post from Norway's main science and tech university highlights the amazing adaptations that allow birds, such as the ptarmigan, to survive the frigid winters there and elsewhere near the poles.

Surviving the cold is particularly difficult for small critters, because:
  1. they need to eat more often that large ones. Small birds tend to have high metabolic rates, which keeps them warm but requires more energy.
  2. they lose heat faster than larger-bodied animals because they have more surface area (where heat is lost) compared to the volume of heat-producing tissue (e.g. muscles, etc) in their body.
  3. they can't store as much fat, which means less insulation and even more heat loss.
  4. birds, in particular can't build up too much fat if they want to continue flying.

the morning after: a ptarmigan snow burrow
photo: Olav Hogstad, NTNU
Since survival in the Far North is all about preventing this heat loss, the ptarmigan and her friends in Norway have evolved several strategies for surviving frigid temperatures:

Use the Snow:

The willow ptarmigan, as well as her friends the wood grouse, black grouse, hazel grouse, and other game birds, create and sleep in their own shelters in snow caves or burrows.

Snow insulates well, so the birds stay much warmer in their small caves than if they were to sleep in the open. When it's really cold, the birds dig down into the snow, where they stay to survive and protect themselves from the cold.

Like the field mice and voles that dig burrows into the snow and rest in trapped air pockets there for the winter, even small birds have learned to burrow into the snow to stay warm.

One of them, the 5-inch (13 cm) long mealy redpoll, digs a system of snow tunnels to stay alive through long winter nights as well.

a mealy, or common, redpoll
(named for the red on his forehead).
Yes, this bird digs and sleeps
in snow tunnels to stay warm.
photo: Cephas, Wikipedia

From Norwegian professor Olav Hogstad: A willow tit in deep sleep
in a small cave. It’s about 20 degrees below freezing outside.
Its feathers are puffed up to create an insulating layer of air
around its body, and it has stuck its beak into the feathers
along its back, to avoid breathing in the freezing cold air.
photo: Gunnar Nilsen

Lay low:

A number of northern mammals - including the northern birch mouse, some bats, hedgehogs, and, of course, bears - hibernate in the cold winter months.

just like the willow tit, a black bear
curls up in its den
photo: North American Bear Ctr
Willow tits also save energy by slowing their metabolism on really cold nights, lowering their body temperature from roughly 41 degrees C (105 F) to 31 degrees C (88 F). Using less energy retains precious heat, which allows these little birds to survive the night.

If a bird’s temperature falls too low, however, it will die; willow tits have a finely tuned thermostat that starts a bird's body shivering when its core temperature reaches 32 degrees C. The shivering activity produces heat that allows the bird to stabilize its core temperature.

Fix a hole

Not all birds can slow their metabolism or burrow into snow. Woodpeckers peck out special holes to sleep in, while other birds look for sheltered spot under a snow-covered tree branch.

For those, such as great tits, that can't make their own sleeping holes, competition for the limited safe, warm places to sleep can lead to fighting at twilight over the best sleeping spots.

Snuggle up

From a case of 30-40 Eurasian wrens roosting together
in the mud nest of a House martin.
illustration: Ad Cameron
The Eurasian wren is one of Norway’s smallest birds, so even quality sleeping sites might require extreme measures for winter survival. Groups of these birds will huddle together under the snow or in holes to survive the long nights.

Above ground, Eurasian treecreepers will also sleep in tight groups in the nooks and crannies and cracks of trees.

Scientists observe aggression within these groups, as if the birds don't really enjoy such close quarters. Birds can and do freeze to death here - surviving the night is most important, so they likely ignore their differences and stick together.

Ptarmigans and their grouse cousins can even snuggle up to themselves, growing extra thick plumage with a heavy insulating layer of feathers, even on their feet. Their scientific name (the genus),Lagopus, which means "hare foot" in Ancient Greek, refers to the ptarmigans' feathered feet and toes (snowshoes!) that look like rabbit feet.

ptarmigan going incognito (i.e.molting) getting ready for spring
photo: George Powell
By growing white feathers, ptarmigans put on a coat that not only provides protective coloration against a background of snow, but it also improves insulation, as white feathers are hollow air pockets that help protect against the cold.

When spring finally arrives, they put on a different disguise that protects them both from all those mammals that are waking up from their long sleep and the eventual heat of summer.

It's quite a process, but one that has enabled them to thrive all over Europe, Asia, and North America.

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