Birders are a flighty bunch.

Especially when word goes out on the hot line that a hepatic tanager or a Mongolian plover has been sighted near Los Angeles.

Serious bird watchers like Nancy Pachana and Tim Kastelle of Encino will drop what they're doing and rush off to some remote Los Angeles County mountain road or to a strawberry field outside Oxnard to take a look.

That happened the other day when the couple cut short a long-planned bird-sketching expedition at Malibu Lagoon. After spotting five species of gulls and four species of terns, they folded their scopes and beach chairs and hurried off to Carbon Canyon Park near Brea.

"We hear there's a scissor-tailed flycatcher down there," Pachana explained to professional wildlife artist John Schmitt, who was in charge of the outing.

No apology was necessary, replied Schmitt, of Norwalk. "A friend called to tell me a dusky warbler has been seen up at Vandenberg Air Force Base. It's going to attract a lot of people, too."

Despite its heavy traffic, sprawling subdivisions and growing human population, Southern California is still considered a bird paradise. And this is the time of year when birders feel they're in paradise too.

"Fall is when birds are moving. This is the time of year when you have your greatest chance here to see birds that are out of range," Schmitt said. He is a globe-trotter who has observed more than 800 species in a birding career that began at age 4 when he tried to rescue a blackbird that had been hit by a car outside his Long Beach home.

There are about 9,500 species of birds worldwide. Experts say about 450 species can be seen in Los Angeles County--counting migrating and "vagrant" birds that get lost and fly in by mistake.

No one keeps track of how many bird-watchers there are here, however. Audubon Society officials and other experts say there is no doubt that the number is growing. So is the quality of birds being sighted.

That's because birders no longer have to wing it when they head outside with their binoculars.

Five "bird alert" hot lines listing when and where rare birds have been sighted are operated by Audubon groups in Southern California. At least one is updated daily.

Some bird lovers subscribe to computerized notification services that automatically dial their telephone number when there is news of an unusual sighting. The computer keeps calling until either the birder or a message machine answers.