Page:Popular Science Monthly Volume 49.djvu/356

338 There are several reasons why birds require so much food. They are active creatures, being almost constantly in motion some individuals traveling many miles every day. Of all animals, their blood is the warmest; their temperature is about five degrees



higher than man's. This heat of the body is nicely protected by their covering of down and feathers, but it requires more food to make feathers than to make flesh or hair.

A tiny bird's body is a highly concentrated bit of nature, which is controlled by an intelligent and active brain that keeps his little system in such constant motion that it must be