How Much Fat?
Body fat is a good measure of how healthy a hummingbird is, and how well it is eating. A hummingbird's skin is thinner than a plastic sandwich bag, and just as clear. Under the skin fat is whitish yellow, which shows up easily against red muscles. Nancy holds the hummimgbird upside down (there is more fat on the underside than the back) and blows on the chest feathers. When the feathers part, she can see the skin and how much fat is there.