Several studies conducted by URI physiological ecologist Scott McWilliams have shown that birds have a flexible digestive system that they modify to meet the changing energy demands of migration.

"The gut of a migratory bird is a really dynamic organ. In preparation for migration, the gut increases in size tremendously over several days," McWilliams said. "It expands, its cells get larger and it produces new cells so the bird can dramatically increase its food intake and store up energy for the long flight."

But because the digestive system is one of the most metabolically active tissues in the body and it consumes a great deal of energy, it shuts down during migration so more energy can be diverted to fueling flight. This partial atrophy of their digestive system affects birds when they stop to feed at sites along their migration route. McWilliams says that because their digestive system is shut down, the birds must eat less until their gut becomes acclimated and can operate efficiently again.

"We've known for many years that birds recovering from a migration flight do not immediately regain body mass, but we didn't know why. Now it's clear that this digestive constraint is responsible for the delay and likely affects the pace of a bird's migration," said the Kingston resident.

One important result of McWilliams' research is a new understanding of the protein requirements of migratory birds. Ornithologists have long believed that a diet high in energy was all that was necessary to sustain migratory flight. But the URI researcher said that proteins are also needed to build the digestive tract. This need for protein may have a significant imp
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Contact: Todd McLeish
tmcleish@uri.edu
401-874-7892
University of Rhode Island
7-Jul-2003