MIGRATORY BIRDS VISITING ANGELES NATIONAL FOREST : FEATHERED FRIENDS MAKING THEIR ANNUAL TREK.

Byline: Mary Schubert Daily News Staff Writer

Spring fever is a seasonal phenomenon that overcomes birds as well as humans, because this is the time that winged creatures migrate to local mountains for breeding and nesting, experts said.

Neotropical migratory birds, which split their year between Canadian provinces and assorted countries in Central America, the Caribbean and South America, stop every year in the Angeles National Forest during April, May and June, said JoAnne Webb, a naturalist with the U.S. Forest Service.

On Saturday the Saugus Ranger District will host a bird walk at Frenchman's Flat to mark International Migratory Bird Day. Doug Martin, from the San Fernando Valley chapter of the Audubon Society, will lead a hike along Piru Creek to point out numerous species of neotropical migratory birds.

Those who attend the free event, beginning at 8 a.m., are advised to bring binoculars and bottled water and to wear sunscreen and either hiking boots or sneakers.

``We should be able to see 70 or 80 different species of birds, a lot of which are still passing through - but some of them are breeding and nesting. They come to North America to breed. It's just kind of a mysterious urge to come here to breed,'' he said, noting there isn't any particular climatic or habitat-related reason for the birds to leave their neotropical countries each year.

``They fly north during the spring and summer months here because the conditions for nesting and breeding tend to be ideal for that sort of thing,'' said Bill Brown, a U.S. Forest Service biologist.

Among the varieties that visit Southern California this time of year are Northern orioles, warbling vireos and Costa's hummingbirds, Martin said. The birds like Frenchman's Flat and Piru Creek because the area has a supply of water, food, shelter and nesting sites, he said.

The birds typically spend about a week building their nests. Depending on the species, they lay four to eight eggs and then incubate them for two to three weeks until they all hatch, Martin said.

Once the young are born, they remain in the nest another two or three weeks until they are strong enough to fly. Then, Martin said, the baby birds spend about a month in the area learning to fly - and once that technique is mastered, the migration resumes.

``Usually, the (adults) migrate to the place where they'll breed - their northernmost point,'' he said. Shorebird varieties tend to fly through California en route to Alaska, where they breed before returning to Mexico, Argentina and other neotropical countries for the winter, Martin said.

``When the weather starts getting cool here and there aren't a lot of insects and blooming flowers to feed on . . . they head south, down to Central and South America, where they can find the food they need,'' he said.

``A lot of the birds you'll see here this time of year are just passing through. Some birds go all the way from South America up to Alaska because it's daylight for long hours, which helps them provide a lot of food for their young.''

While the birds eat and rest during daylight hours, they fly by night.

``They navigate by the stars,'' Webb said.

``Birds tend to migrate en masse at nighttime. There's kind of a celestial navigation that they use,'' Brown added.

``The one thing I know about bird-watching is that it's becoming one of the fastest-growing pastimes,'' Webb said. Piru Creek is among the best spots in the Santa Clarita Valley to spot the migrants, she added.

The Northern oriole, Martin said, is a bright-orange-and-black bird with a white stripe across its wings. It winters in Central America, coming to California's foothills and parks to breed.

``They build these really neat hanging nests,'' he said.

Warbling vireos are plain, sparrow-sized birds, ``but they have a really beautiful song,'' Martin said.

Costa's hummingbirds are one of that breed's smallest, and are distinguishable by a bright-purple patch on their throat. ``They come here when the sage starts blooming. They love to feed on sage nectar,'' Martin noted.

Migratory birds tend to fly along riparian - stream - corridors, Brown said. ``All the things they need to survive tend to be in those areas: There's food, water and cover . . . and travel routes that the species can follow up and down,'' he said.

``There are approximately 340 bird species that migrate between wintering grounds in Mexico, Central America, South America and the Caribbean and summer breeding grounds across North America,'' Webb said, citing the Audubon Society's Field Guide to North American Birds as a reference on their species and habits.

``There has been a large decline in the migratory bird population in the last 10 years due to habitat destruction,'' she added.

For information on the bird walk, call the U.S. Forest Service's Saugus Ranger District at [phone]. Frenchman's Flat/Piru Creek is at the gated dead end of the old Golden State Highway, a road that begins a block west of the Templin Highway exit of Interstate 5.