Remember the 50’s musical “Singin’ in the Rain” where Gene Kelly sings the title song while being pelted by raindrops? It is one thing to sing and dance in the rain with an umbrella and quite another to live in it as do birds. How do they do it? A storm comes in on a low pressure center; this makes it more difficult for birds to fly simply because the air is less dense. Rain, or even water vapor (humidity) takes up more space, resulting in even fewer air molecules. This is why birds perch before and during a storm – it takes a lot more energy to fly in rainy conditions and so they avoid doing it. They perch in a tree, in shrubs or wherever they can get some protection. One scientist observed songbirds on the ground and huddled under shelter during Hurricane Katrina. But they also sit on power poles and lines where they face the wind and reduce their resistance to it.
Birds are waterproof. Their feathers, made of protein similar to our fingernails, have interlocking barbs to make them both flexible and water resistant. Feathers overlap one another like roofing tiles to make the bird both aerodynamic and water repellent. Birds also have an oil gland at the base of their tail which they use to put a waterproof coating on their feathers. You may have seen a bird reach over its back as if it was scratching an itch on its tail; it is actually squeezing oil from the gland which it then spreads over the feathers. The outer feathers of birds protect the insulating feathers underneath, just if they were wearing a down jacket with a waterproof shell. Some birds, like egrets, have what is called “powder down”, fine granules like talcum powder that are produced by the decomposition of special down feathers and repel water. And birds have a third eyelid, a translucent membrane, which allows them to face the rain with protected eyes. Birds also have a special mechanism in their legs, a tendon that causes the toes to curl when they perch, giving them a tight hold on a tree branch in the blustery wind.
So birds do fairly well during a rainstorm, at least for a short time. But if the storm is particularly windy, rainy, or cold, or lasts for more than a few days, birds begin to show the effects. No one really knows how many birds die during a storm or series of storms. But mortality is certainly higher than usual. They fly into trees or windows, they get lost and wind up over the ocean or a large lake, their food sources are made more difficult to access at the same time they need more food to get warm, and they are more vulnerable to predators. So they hunker down and fly only when necessary.
An old proverb says “When the goose honk high, fair weather; when the goose honks low, foul weather.”