As the NE recovers from the first blizzard of the season, one is again amazed at the survival mechanisms of our feathered friends. As years go by my toleration of the bitter cold has decreased–I wonder if an aging bird feels the same way. Birds are warm-blooded like us, but have developed some special adaptations. So how do they survive?
1) Migration. That’s an obvious solution (and one I personally endorse), but it isn’t without risk. Heading south actually is quite risky for birds and takes tremendous amounts of energy and luck to make the trek. Predators take a toll as the long trip often leaves the bird weak and vulnerable. The migrator also leaves its breeding territory to others, possibly never to get it back. But migration is primarily to follow food sources rather than to avoid the cold. Ducks, waders, and shorebirds need open water and head south as far a necessary to find it. Migrating birds that depend on a diet of insects head south to follow the bugs, whereas the non-migrating birds have the ability to digest seeds and can stay north. Some eat both and change their diet with the season–Yellow-rumped Warbler is an example of that and the only warbler commonly seen here in winter.
2) Behavioral Changes. Bird survival in cold weather is all about energy management. Energy comes from food, and to a lesser degree stored fat. Searching for food however burns energy. They need to eat something, but must find the food quickly and efficiently–no random flying, casual singing, or mating this time of year. Birds can only store small amounts of fat as too much fat interferes with flight. Fat birds don’t fly.
Some more sociable birds like chickadees huddle together to share some warmth, similar to the Eskimos and the famous ” Three Dog Night”. Staying out of the wind at night, and basking in the sunshine by day helps. Getting food from a feeder is usually not necessary for survival, but on the very cold night when there is a new deep snow cover, it may be life-saving.
3) Insulation. Feathers are an amazing adaptation for birds, not only light-weight and necessary for flight, but also a great insulation from the cold. They need to kept dry, hence the oil that sheds water. On very cold nights you’ll see them fluffing them out to increase the R value.
4) Internal. Birds are warm-blooded but have a core temperature significantly greater than humans, averaging 106 F. Some species however have developed a night-time torpor, almost a semi-hibernation, lowering their temperature as much as 20-30 degrees in the case of hummingbirds. Shivering can also generate some additional heat.
But even with all these mechanism, some won’t survive the frigid nights. Small birds are especially vulnerable since they have relatively greater surface area per weight and therefore lose more heat than larger birds. We’ll never know for sure, but I’ll bet the bird mortality in New England was high this week. C’est la vie, c’est la morte.