Friday, July 3, 2009

Green lake grebes eating feathers

As of 10 a.m. today, there were three babies and one egg in the pied-billed grebe nest. Here the adults are singing a duet, while the babies swim toward them.

Martin Muller emailed me with this fascinating point about the feather seen on the baby's bill in Wednesday's pictures. He wrote that grebes eat their own feathers, and that their flank feathers molt constantly, giving them a steady supply.

"All grebes will eat their own feathers as well as some 'found feathers' (for instance when ducks are molting and many small feathers are floating around). Sometimes the very first 'meal' a newly hatched grebe chick receives is a feather the adult provides.

Feathers line the inside of grebe stomachs and also provide a 'plug' in the pyloric exit (stomach to small intestines). The feathers are thought to provide protection from sharp fish bones (adult grebes swallow fish whole and they slowly dissolve in the stomach acid, youngsters are proffered smaller pieces of fish but those may contain fish bones too), as well as a 'strainer' to keep the partially digested food inside the stomach long enough to dissolve.

A third theory postulates that the feathers provide bulk for pellets (grebes regurgitate pellets containing indigestible matter like chitin shields of insects they eat, or plant material ingested along with animal mater). The pellet is also thought to clean the esophagus of parasites as it works its way up and out (like the sponge that is sent through pipes, using water pressure, to clean the inside of the pipes at dairy farms, hence the name for the theory 'polishing sponge theory' -translated from the original Dutch 'poetsprop theory'-)."

Here's an adult feeding a youngster a feather.

Previous posts:

June 3: one egg.
June 10: seven eggs.
June 27:first hatching.
June 28: second hatching.
June 30: three babies, two eggs
July 1: still three babies, two eggs

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