Birds belong to the animal kingdom. They are vertebrates — animals that have a definite head, a backbone, and a well-developed brain. In addition, they are warm-blooded, have forelimbs modified as wings, though some birds such as penguins don't fly, and skin covered with feathers. The number of feathers increases with size. Black-capped chickadees have around 3,000 feathers, and tundra swans more than 25,000.
The high metabolism of birds makes them good litmus tests of the quality of our air, water and soil at most any time and place. An estimated 200 billion-400 billion birds live on Earth. That is close to 14 times the human population. They range in size from the 300-pound ostrich, standing near 8 feet, to the bee hummingbird, measuring a 2.2 inches. A majority of small land birds travel at speeds between 20 and 30 miles per hour, while the flying speed of ducks and geese ranges from 40 to 55 mph.
Birds have a good sense of hearing, but they have relatively poor senses of smell and taste — witness American crows feasting on road-killed skunks.
There are about 9,700 species of birds. About 650 species of birds are found in North America. Close to 300 could be observed during any one year in Minnesota, where about 240 species are known to nest. However, only about 60 species usually spend their winters in our state. A person can observe up to about two dozen species coming to feeding stations from May to July.
Jim Gilbert's Nature Notes are heard on WCCO-830 at 7:15 a.m. Sundays. He has taught and worked as a naturalist for 50 years.
