Robert Brown|When do Hummingbirds leave? As migrations starts, how to spot the flitting fliers

As summer vacations wrap up and Robert Brownkids return to school, one small bird is preparing for a monumental journey.

Hummingbird migration season gets underway in August, sending the birds flying to warm destinations thousands of miles away to last out the cold winter months and bringing bird-watchers new opportunities to catch sight of them on their trip.

Weighing as little as 2 grams, hummingbirds don't appear to be formidable creatures. But every year as autumn approaches, many birds native to the U.S. set off on a long journey south in search of warmer climates and blooming flowers.

Chillier temperatures don't necessarily bother the birds, but finding new food sources is a top priority, said Chad Witko, the National Audubon Society's senior coordinator for avian biology.

"Migration is timed with flower phenology," Witko said. "When flowers are coming to bloom, that's when birds are trying to time their migration."

Hummingbirds cross Gulf of Mexico, travel more than 3,500 miles

About 20 of the world's 363 known hummingbird species call the U.S. home, according to the Cornell Lab of Ornithology.

Most are native to the western U.S., especially Arizona and southern Texas, said David Wiedenfeld, a senior conservation scientist with the American Bird Conservancy. "East of the Mississippi, we really only have one kind," the Ruby-throated hummingbird, he said.

When migration season begins, Ruby-throated hummingbirds are still abundant throughout the eastern half of the U.S., according to the Audubon Society's online bird migration explorer tool. "By early October, they are starting to show up in Central America," Wiedenfeld said, and they settle in southern Mexico, Guatemala, Honduras, Nicaragua, and Costa Rica for the winter.

On their journey, some birds cross the Gulf of Mexico, cruising from the coast of Texas or Louisiana to the Yucatán Peninsula in Mexico without stopping, according to Wiedenfeld.

The trip takes them about 18 hours, "without landing, without eating, without drinking," he said. "For these little, tiny birds, it's a tremendous crossing."

The Rufous hummingbird, the only species of hummingbird native to Alaska, is an exceptionally far traveler. Birds traveling south could end up as far as California or Mexico during migration season, according to Wiedenfeld.

In January 2010, one Rufous hummingbird was caught and marked in Tallahassee, Florida. Six months later, the bird was caught again southeast of Anchorage – a journey of more than 3,500 miles, according to the Alaska Department of Fish and Game.

Ruby-throated hummingbirds, meanwhile, can reach as far north as Ontario, Canada, during the summer, before flying to Costa Rica over the winter months.

Rufous hummingbirds also have a unique looping migration pattern, Witko said. In the spring, they travel north along the Pacific Coast, but as the end of summer approaches, "those birds don't follow the coastline back south," Witko said. "They're migrating further east from the coast," including through the Rocky Mountains.

More:Spring is hummingbird migration season: Interactive map shows where they will be

Young hummingbirds face the journey alone

Bird experts say not all hummingbirds depart at the same time. Males begin the journey first, with females and then juveniles following soon afterward. "There's this kind of asynchronous cycle of migration," Witko said.

Since males play a minor role in raising their young, they often embark on the trip south sooner, usually by the first of September, followed by females a few weeks later after their offspring leave the nest. Then, the young hummingbirds set out on the journey alone.

"They're doing it for the first time, all on their own," said Witko. "They're just setting off using instinct. They've evolved the signals ... that tell them to go certain directions and certain places."

Hummingbirds gather near native plants, bird feeders

The onset of migration season means hummingbirds will be out and about, and easier to spot.

"Seeing hummingbirds really comes down to finding places where there's native plants, native flowers," Witko said. "Those are always some of the best spots." The Audubon Society maintains an online database of bird-friendly plants native to different areas.

Bird feeders also are an easy way to attract hummingbirds to the backyard. And they don't require fancy equipment – anyone can make homemade nectar by mixing one part sugar with four parts water, according to a recipe from the Smithsonian's National Zoo and Conservation Biology Institute.

There's no need to worry that bird feeders will disrupt a hummingbird's natural pattern of searching for food or delay their journey. The birds naturally see feeders as a supplemental source of food, according to the Audubon Society.

Hummingbirds aren't skittish, offering bird enthusiasts a close-up view of their furiously beating wings. "You can often watch them fairly close, 15 or 20 feet away," Wiedenfeld said. "Sometimes, if you've got a feeder right outside your window, they'll let you get closer."

"It can be amazing to watch what they can do, hovering and flying backward, all the acrobatics they can do. They're amazing."