Taking the long way
Rufous and Ruby-throated Hummingbirds conquer mountains, brave deserts, and cross the Gulf of Mexico
Published: February 20, 2009
|Only a handful of the roughly 330 hummingbird species in the world truly migrate. Most live in the tropics year-round and don't need to travel far from breeding to wintering grounds. |
North America's hummingbirds, however, are a different story. Most of our species migrate north in spring to breed and south in fall to more hospitable wintering areas.
In fact, two of the more common hummingbirds, Ruby-throated and Rufous, have the longest migrations in the hummingbird world. They cross the Rocky Mountains, the deserts of the Southwest, and the Gulf of Mexico.
The migration of Ruby-throats can be about 5,000 miles round trip. They nest in the forests of the eastern United States and in Canada from central Alberta to Nova Scotia. In fall, they head to forests from Mexico to Costa Rica, while a few winter in southernmost Florida.
Perhaps the most amazing migratory feat is the Ruby-throat's well-known crossing of the Gulf of Mexico. Beginning in late February and early March, the birds depart from the Yucatan Peninsula at dusk with huge flocks of songbirds. They cross 500 to 600 miles of open water non-stop, arriving the next day from Louisiana to Florida.
Research suggests the trip takes about 15-18 hours, but hummingbirds, which weigh only about 3.5 grams (one-eighth of an ounce), are too small for satellite transmitters, so no one really knows how much time it takes. For a week to 10 days before the crossing, the birds fatten up on nectar and insects, almost doubling their body mass to about 6 grams (about a fifth of an ounce) for the long flight.
Notably, not all Ruby-throats cross the Gulf. Many of them follow an overland route through Mexico and Texas, arriving in the U.S. at nearly the same time as Gulf transients. (In fall, the bulk of the migration is over land, but specific routes are not well understood.)
The land route may offer birds food security, but it also adds hundreds of miles to the overall journey. While it may seem odd that a 3 1/2-inch-long forest bird would evolve an enormous over-water migration route, the advantage appears to be speed: Take the fast lane to the breeding range, and you could have first dibs on the best territories.
The migration of Ruby-throats is studied in a few places. Counts are done annually at Hawk Mountain Sanctuary in Pennsylvania, the Hilton Pond Center for Piedmont Natural History in South Carolina, and at Holiday Beach in southern Ontario on the northwestern shore of Lake Erie. Large numbers seen at Holiday Beach suggest many birds fly around the western end of the lake to avoid crossing it. At Hawk Mountain, some Ruby-throats follow the ridge south through the Appalachians.
Observers have found that Ruby-throats cruise below about 500 feet - lower than the migrations of most songbirds. Flights occur in the daytime and often peak after 10 a.m. Researchers hypothesize that the birds must feed heavily on nectar in the early morning to fuel their migration for that day.
We usually see hummingbirds hovering at or near our backyard feeders. The mode of flight used in migration, however, is very different. Instead of continuously flapping their wings, as in hovering and short flights, during migration the birds bound. That is, the wings stop intermittently and are either drawn into the body or held out as in gliding. The bounding flight is similar to that of woodpeckers, warblers, and many other small birds.
In terms of migration distance, no hummingbird comes close to the flight of the Rufous. A round-trip journey from the northern edge of the breeding range in southern Alaska to the southern edge of the wintering range in south-central Mexico would cover almost 8,000 miles. If we measure the distance in body lengths, says the Handbook of the Birds of the World, then the species holds the world record for the longest migration performed by any bird.
Small numbers of Rufous Hummingbirds winter throughout coastal Texas east to the Florida Panhandle. And more than any other western hummingbird, the species shows up as a vagrant in the east, straying as far north as Maine and Nova Scotia.
The species also has an unusual elliptical migration. In spring, birds migrate northward close to the west coast at relatively low elevations, and in fall, they migrate southward at higher elevations in the Rocky Mountains. As they migrate in fall, they stop in alpine meadows to feed on flowers that bloom in late summer. The elliptical migration appears to have evolved to take advantage of the blooms, which are available only during fall.
Considering how far they fly and how well adapted they are to migration, is it any wonder why hummingbirds fascinate so many birdwatchers?
Vagrant: An individual found outside the normal winter, migration, or breeding range for its species.
Elliptical migration: Migration along a non-linear path that generally is farther east in fall and farther west in spring.