When we look at the sky, it’s like a roof – flat, solid – just sort of there. Unless the light is exceptional, even clouds and constellations looked painted on it.
For the birds though, the sky isn’t flat, it’s multidimensional. Just as different bird species hunt at different levels within the same tree, different birds tend to fly at different levels in the sky. And for them, the clouds aren’t just pretty puffs in the sky. They are a dynamic part of their daily landscape.
Flying high exposes birds to dangers, such as higher winds or hungry hawks. So when not migrating, most birds follow the facetious advice often given to new pilots, they “fly low and slow”, usually under 500 feet. But during migration, birds often climb to remarkable heights, probably to conserve energy. They burn fewer calories in the cooler air and become dehydrated less quickly.
Also, winds that can hinder day-to-day activities become a welcome aid to quick travel. Like pilots, birds seem to know that their optimum cruise altitude increases as their “fuel” is consumed and their weight declines. Long-distance migrants seem to start out at about 5,000 feet then progressively climb to about 20,000 feet. In the Caribbean basin, where considerable radar work has been done, migrating birds are most often observed at about 10,000 feet.
Clouds and Birds:
Altocumulus clouds: Migrating swans and geese are known to sometimes fly more than 25,000 feet above sea level , over four miles high!
Stratocumulus clouds: Broad-winged Hawks routinely soar at around 3,200 feet, aided by thermals created by differing ground temperatures.
Cumulus clouds: Vultures sometime rise to over 10,000 feet, scanning wide areas for food and watching the behavior of distant birds for clues to the location of a feast.
Cirrostratus clouds: Jet planes typically cruise at about 35, 000 feet, in what are commonly known as “ice clouds”.
Nimbostratus clouds: In their daily activities in and around our backyards, many of our favorite songbirds stay in the 30-to 50-foot range above the ground. Robins, bluebirds, jays, woodpeckers, chickadees, and nuthatches are all relatively low flyers.