The condition is caused by the failure of developing nerve cells to migrate normally.

They do not normally migrate other than for local movements, such as altitudinal migrations in the Himalayan species (Mead 2003).

Pinworms cannot damage the skin, and they do not normally migrate through tissues.

Manatees normally migrate northward to the Carolinas, but they rarely go farther north.

Predators in suburbia are few, and Mr. Butler said the fall hunting season tends to bring down more of the normally migrating birds.

All the suspected EU outbreaks so far involve swans, a species that does not normally migrate outside Europe.

At the appropriate times of the year, caged migrant birds regularly hop in the direction relative to the sun in which they would normally migrate.

When warblers were kept under constant lighting conditions, they continued to become restless at the times when they would normally migrate.

Ducks do not normally migrate from east to west, but "there are occasional westward migrations according to the weather," Dr. Thiermann said.

Swans in southern Italy do not normally migrate, he said, but their wetlands are along many bird migration routes.