Science Sunday: Birds Of A Feather Migrate Together, But Not Hummers

Our hummingbird friends have departed for the winter, which for us marks the beginning of the extraordinary annual avian migration from the northeastern U.S. to warmer climes.

About 1,800 of the world's 10,000 bird species are long-distant migrants. Most use established flyways, typically along mountain ranges or coastlines to take advantage of updrafts, a behavior that is part genetically programmed and part learned.

The birds fly north in the spring to breed and raise their young during longer daylight hours and return in the fall to winter in warmer regions with stable food supplies, but the timing of migration often varies from year to year because of variances in the weather.

Does the fact that our hummers left a little earlier this year than usual foretell an early winter? Probably.

Scientists have ascertained that hummers are very conscious of the changes in daylight and corresponding decline in inspect and flower populations, as well as a chemical change that compels them to migrate.

Our ruby-throated hummers -- the only hummingbird species in the northeastern U.S. -- will gain 25 to 40 percent of their body weight by gorging on insects and nectar before the start their southward migration to Mexico and Central America. And while larger birds tend to migrate in flocks like Canada geese, hummers share the same flyways but are loners. There is a reason for this: They are so small that most predators have difficulty seeing them if they don't flock together.

Hummers also are unusual in that they make frequent stops to feed and do not fly very high off the ground, typically just above treetop level over land and skimming just above the surface over water.

They also fly during the day and rest at night, but large bodies of water do not allow them that luxury so they must keep on going. The Gulf of Mexico is a particular challenge in this regard, but these tiny fluffs of feather find a way to navigate a 450 mile stretch of water, which translates into more than 20 hours of travel time.

Amazing!