Tuesday, April 17, 2012

Birds and Weather

We've heard a lot of concerns about weather from nest watchers.  Following the nicest March anyone in the American Midwest can remember, we've had tornado outbreaks, high winds, damaging storms, large fires, and snow. The Decorah Bald eagle nest has been tossed around by wind, the Fort St. Vrain eaglets died of exposure following a spring storm, and the Dairyland Power Genoa cam was damaged by lightning. We get asked daily if we can't do something about the weather: shore up nests, build roofs, and even take young birds from their nests. The short answer: No. I wrote about intervention in an earlier post. We intervene in the case of obvious, acute danger, but weather is a chronic condition that all of us have to live with.

High winds, severe storms, and fire are nothing new. If animals couldn't survive them, they wouldn't be here. The birds we watch are well prepared for the weather challenges they face.
  • It's Cold and Wet! Feathers are wonderful insulators and adult Bald eagles have roughly 7,000 of them. Light and fluffy down feathers trap air, while flight feathers hook together like a zipper, forming a continuous 'vane'. Preening releases an oil that coats the outer layer of feathers, which further protects adult birds from moisture: the outer feathers may get wet, but the bird's body does not. We've watched the adult eagles shake off rain and sleep under a blanket of snow. They are well prepared for cold, wet weather.

    As of this post, all of the Decorah eaglets have their second down. Unlike the first fluffy white down, the 'wooly' second down has insulative properties. Mom and Dad will still protect the eaglets from rain and snow, but they are able to thermoregulate now.
  • It's Hot! We've had a lot of questions about panting this spring. Like dogs, eagles don't have sweat glands. They control heat by panting, radiation through their unfeathered legs and feet, and perching in the shade. March was unusually warm and the cottonwood doesn't leaf out until April, so the eagles spent a lot of time in direct sunlight. We also got to see a little more of the eaglets than we usually do: many cam watchers commented on how lively, naughty, and busy this year's brood has been. The dry, hot weather means that the eaglets spend more time exploring the nest than huddled under Mom or Dad, and everyone spends more time panting.
  • It's Windy! Adults and young hunker down against high winds and storms. Some of their behavior appears instinctive and some is learned. The first year Mom nested here, she turned tail to the wind and was blown out, nearly taking a young eaglet with her. That hasn't happened since. The adults minimize their profiles during high winds, keeping wings tucked in, tails low, and young birds protected. Young birds curtail nest exploration and play, sheltering under Mom or Dad until the wind dies down.  When the adults do get pushed around by sudden wind gusts, they don't grab at the eaglets, and the eaglets are not especially aerodynamic at this point.

    We've also heard from watchers concerned that the Decorah Bald eagle nest will fall/has fallen. The nest weighs approximately 1300 pounds, is tightly woven of strong wood, and is wedged securely into the limbs of a cottonwood tree. The tree is healthy, with no large dead limbs, and near a good water source.  Can we say that the nest will never fall? No. But is it likely to fall? Also no. The nest is very secure and the tree is healthy and relatively secluded from wind. If the nest or tree did go down, we'd be on site as quickly as we could.
In short, we can't do anything about the weather. Fortunately, the birds we watch are equipped to survive it in all but the direst cases. The Decorah nest in particular benefits from an ample food supply, experienced parents, and a relatively sheltered location. Last year, we watched them respond to cold weather and late snowstorms. This year, we've watched them respond to warmer, windier conditions: they've spent more time off the eggs and young babies, and their 'hunker down' time has been more likely to be a response to wind than rain or cold weather.

Here are a few videos that show the Decorah eagles under various weather conditions:
Things that helped me write and learn about this topic:
If you would like to learn more about how animals survive cold weather, I highly recommend Winter World: The Ingenuity of Animal Survival by Bernd Heinrich. If you would like to know more about animals in summer, I highly recommend Summer World: A Season of Bounty, also by Bernd Heinrich.
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