Yellow-chevroned parakeets flock in the Sepulveda Basin's willows and cottonwoods, and red-crowned parrots have found a habitat among the streets and alleys of Pacoima and Van Nuys.

An exotic population of parrots and parakeets native to South America and parts of Mexico is living wild and free in the San Fernando Valley, apparently escapees from captivity -- or their descendants -- that have learned to feed off trees and plants in back yards and parks.

"Most bird-watchers are aware they're here so they expect to see them," said Kimball Garrett, ornithology collections manager at the Natural History Museum of Los Angeles County.

"But the general public -- well, a lot of them are coming to realize that just like palm trees and everything else, it's just part of the artificial landscape of this area."

One oft-repeated speculation is that some of the Valley's parrots and parakeets stem from Busch Gardens, the Anheuser-Busch amusement park that treated visitors to the Van Nuys brewery to boat rides and exotic bird shows from the 1960s to the 1980s.

An Anheuser-Busch spokesman said the story is untrue. Escaped tropical birds are found elsewhere in the United States, he said.

"It is an urban legend. There may well be parakeets in the San Fernando Valley but they're not the descendants of Busch Gardens birds," said Fred Jacobs, spokesman for the Anheuser-Busch theme park division.

The red-crowned parrot, the only parrot or parakeet that has been added to the official list of avian species that live in California, is the most numerous tropical bird in the Valley.

Red-crowned parrots could number from about 70 into the low hundreds, Garrett said. Predominantly green with a red patch on the head, the birds grow to about 12 to 13 inches and live in Pacoima, Sylmar and Van Nuys.

Garrett is studying the yellow-chevroned parakeet and is trying to take a count. They grow to about 8 inches and are lime-green with a yellow patch on each wing. They live in the Sepulveda Basin and neighborhoods east of that, including Studio City and Glendale.

The yellow-chevroned parakeets, which make squeaking chirps, have been seen in groups of up to 50 in the Sepulveda Basin.

"When they turn, they all turn the same way, and you'll see a burst of green suddenly flashing yellow," said bird-watcher Louise Epps, a clinical psychologist who is second vice president in the San Fernando Valley Audubon Society.

Another newcomer species is the blue-crowned parakeet, which was estimated a few years ago to number 25 birds around Northridge, Garrett said.

Blue-crowned parakeets used to descend six or eight at a time on the coral tree in her neighbor's back yard, said Carolyn Oppenheimer, former president of the San Fernando Valley Audubon Society.

"Oh, they sounded screechy. They were loud and screechy," said Oppenheimer, a retired teacher.

The parrots and parakeets eat seeds and nectar from trees such as the eucalyptus and the silk floss, as well as figs, berries and apricots found in back yards.

Exotic birds are more commonly found in older neighborhoods with well-developed trees, but experts are not exactly sure why they concentrate in certain areas.

The San Gabriel Valley has more tropical birds than the San Fernando Valley, but the birds have been seen in both areas for decades.

"A lot of the populations seem to be growing," Garrett said. "We're not exactly sure why, other than the urban habitats keep expanding."