by Geoffrey Carpentier
Well, we seem to be in a bit of a deep freeze at the moment. I know I don’t like waking up to these temperatures and shudder when I slip on my coat, gloves and toque to fill the bird feeders or take out the recycling. But as I marvel at my own resiliency to deal with the cold, I wonder how tiny birds, like chickadees, survive when the temperature drops to levels which could easily kill them.
This past Sunday, I was conducting a mid-winter waterfowl survey for Environment Canada, to monitor the health of Great Lakes ducks, geese and swans. I must admit while standing on the lakeshore, I was literally chilled to the bone, while all around me Mallards and Canada Geese seemed to go about their business as if nothing was amiss. All was good in the waterfowl world or was it? A strange movement caught my eye at Whitby harbour. Thousands of geese roost here every day, loafing, preening, sleeping and periodically flying out to the adjacent corm fields to feed. Most of the birds had left for their morning snack, but one goose was doing something I had never seen before. It was sitting in a tiny open patch of water, barely as big as its belly and it started to spin. It spun quite fast and repeatedly completed full circles while it swam in this gradually enlarging patch of water. At one point, it stopped assessed the progress and again started to spin, until the hole was big enough for it to swim in without fear of getting frozen in! Nearby a Mute Swan had been sleeping and seemed at peace, until it started to shake its head aggressively. Finally, when it lifted its head to a point where I could see what was happening, I saw that its entire beak was encased in thick ice! The bird continued to shake its head but to no avail. We could not help it as it was well offshore, but later when we returned, we could see the ice was gone and the bird was okay. I’m not sure how that happened, maybe the shaking finally dislodged the ice or maybe the body heat melted it enough that it fell off.
Now back to my chickadees. They appear as tiny balls of fluffy feathers, with bare feet and legs, somehow they never seem to freeze. The answer has to do with how they manage their body temperature, which is very different than how humans do. We try to keep our core temperature constant, and at the same time, keep all our body surfaces warm, including our extremities. The chickadees likewise must consider this, but instead of ensuring the outer extremities are toasty warm they actually maintain the temperature of the legs and feet just above freezing! The blood continuously circulates through them of course, but the heat transfer mechanisms between the cool blood returning to the heart and the warm blood flowing to the extremities is almost 100 percent effective and very little heat is lost, unlike in our bodies. The bird’s core temperature is maintained at about 105 degrees Celsius, a lot warmer than our bodies, so this takes a lot of energy. To augment this, they must eat frequently but must also not waste energy on warming body parts unnecessarily.
The feathers are another part of their warming strategy. Air, trapped between the feathers, stays warm and retains heat very well. The chickadees fluff the feathers up during the day and particularly at night to trap the air and keep themselves warm. Their core body temperature is reduced slightly overnight, so fewer calories are needed to keep them warm, but they may also have to shiver to keep themselves warm and safe at these reduced temperatures. This means each night, they might lose much of their fat reserves just to stay alive. Frequent feeding early the next day is critical for survival.
I want to finish exploring these winter survival strategies, so next column I will continue this discussion.
Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.
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