Alfred Hitchcock’s “The Birds” was on the lips of visitors who ran from flocks swarming over and between trees in the Ameristar Hotel parking lot Thursday night.

Scroll down to view a video of the swarming purple martins

“It must be thousands of them,” said a hotel visitor as she pointed to trees drooping from the weight of the birds.

The purple martins have fascinated casino patrons for weeks, said Bess Averett with Ameristar public relations.

“It’s an awesome thing to see so many birds,” she said.

For thousands to roost in one place is not unusual, said Bruce Reid, director of the Lower Mississippi River Region Audubon.

Though quite small, the purple martin is the largest North American swallow, which spends winters in South America and summers in the United States, said Reid.

They once nested in hollowed old trees, but because so much timber has been cut across the country, artificial gourds and birdhouses have been hung in yards from the Rocky Mountains to the Atlantic Ocean, he said.

“We’ve eliminated their natural habitat,” said Reid. “A lot of people provide housing for them in Vicksburg.”

Averett said the birds roost at Ameristar each year for a few weeks before heading south.

Hotel visitor Veronica Lee of Magee said seeing the flock was “strange” and wondered where they had come from so quickly.

Averett said the birds cross the river from Louisiana around 8 each night and stay in trees there until about 6 a.m.

“They eat all day and roost all night,” she said.

Last year, the birds roosted in trees near the hotel, but Reid showed hotel staff how to regain the property without disturbing the birds.

“We moved our Bradford Pear trees to the parking lot,” said Averett. “We’re trying not to interrupt their migrating habits.”

They arrive in town in early February each year and migrate north to Canada, Reid said.

The birds finish nesting in Vicksburg around July 1 and congregate in groups before flying south, he said, by way of the Mississippi River corridor.

“They like the river environment,” said Reid. “They prefer to feed on dragonflies and other large-body insects.”

Averett said the casino has not had problems with the birds except for the property’s appearance, which is keeping cleaning crews busy.