Sunday's for the Birds: Ever see a chunky chickadee?

Why don’t birds get fat?
Have you ever seen a chunky chickadee; or an obese osprey, or how about a tubby titmouse? The phrase “eats like a bird,” (meaning someone eats very little) is a misnomer. Birds spend much of their time eating, yet they do not get fat. Unlike mammals, bird bodies do not store fat under normal circumstances. Their high metabolism keeps them slim, giving them a necessary weight for flight. Birds burn food energy almost as fast as they consume. Because baby birds have to grow up quickly in order to survive, their metabolism is super high. Parent must feed their offspring constantly during the first few days or weeks after hatching. And during the winter, birds must eat from sunrise to sunset to have enough fuel to keep them warm during the night. 
Whooping Cranes stand 5 feet tall and weight about 15 pounds.

But, given the opportunity, can birds get fat? Absolutely. Birds in captivity, pets or those living in sanctuaries, don’t have the opportunity to burn off calories. If overfed, they can become obese and develop a condition called hepatic lipidosis. These birds store excess fat in their liver cells, causing the liver to malfunction, resulting in distended abdomens, respiratory problems, diarrhea, tumors, and eventually death.
So, keep your bird feeders full and clean. Wild birds can manage their own diets. Captive birds depend on their responsible and knowledgeable owners to keep them healthy and happy.