This often results in annual migrations involving thousands of individuals.

It was cold, too, and the butterflies should have all been gone south on their annual migration.

Recently, for only the second time in 100 years it began spilling onto the peninsula during its annual migration.

The little ones test their wings, and everyone prepares for the annual migration south.

It has been called the largest annual human migration in the world.

Millions of children and their parents made the annual migration during its tenure.

They are monarch butterflies, now on their annual migration north from Mexico.

The annual migration toward northern breeding grounds is expected to last until the end of May.

Now scientists are worried that the great annual northern migration from Africa may bring more illness.

The annual migration is the largest of any Persian tribe.