RED-NECKED GREBE NESTING ON WALDRON POND

Grebes have a quirky feather eating behavior. They pluck them from their breast and belly and feed them to their young starting on the day they hatch. Some chicks will ingest hundreds in the first few days of life, yet they have no nutritional value. Every time the adults preen they too eat some quantity of feathers. It is believed that all of the 22 species of grebes, including this red-necked grebe photographed on her nest at Waldron Pond, eat their feathers.

Why do they do it?

Grebes are among the oldest groups of birds with a history that goes back over 80 million years. They evolved a unique way of digesting their food that later evolved species of birds do not share. Indeed, no other bird is known to eat its feathers. Grebes live on a diet of snails, shrimp, crayfish and other crustaceans, insect and fish, with considerable variation in proportions depending on the species. Their stomach consists of three compartments. Food first passes into the anterior stomach which produces lots of hydrochloric acids and enzymes, facilitating the chemical breakdown of food. Next, it moves on into the middle stomach or gizzard. In most birds, this is where food is mechanically broken down by the contractions of its thick-walled, very muscular structure often containing grit the bird has swallowed. The grit acts as teeth grinding the food into smaller pieces during muscle contraction. By contrast, the gizzard in grebes is thin walled and not muscular. Most of the feathers gather here in the form of a ball which slows the passage of food giving it more time to be digested chemically into a liquid form as opposed to being ground up physically.

A second smaller bolus of feathers is found in the third stomach chamber called the pyloric pouch just at the head of the intestine. These feathers act as a sieve, allowing liquid to entire the intestine while preventing any hard chitinous, scales, bony or other indigestible material from doing so as well as any gastric parasites the bird might have picked up.

Every night the grebes regurgitate and expel a number of pellets containing worn feathers and undigestible animal remains. In this respect, they remind me of owls which also regurgitate pellets consisting of undigestible animal remains.
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