Bridge Is Home for Nest of Rare Falcons

Forty-one years after the last peregrine falcon nest was seen in San Diego, a pair has begun raising a family on a shelf underneath the San Diego-Coronado Bay Bridge.

“It’s just amazing, particularly with the total lack of success we’ve had in the Channel Islands,” said Dan Brimm, a San Diegan who coordinates a program that has released a dozen captive-hatched birds from Point Loma since 1984.

All but one of the birds released in San Diego--the female in the Coronado Bridge pair--went north to make their homes, he said. Five pair of the endangered species have nested in the Channel Islands, off the Southern California coast, for the past two years, he said, but the eggs never hatched.

In San Diego, though, atop a large pillar underneath the eastern end of the Coronado Bridge, wildlife biologist Mark Pavelka spotted three fuzzy chicks last week, said officials of the California Department of Transportation.

Caltrans allowed Pavelka access to a catwalk under the bridge after he saw one of the adult birds sitting on a pole on the bridge April 13, said Steve Saville, a public-affairs officer for Caltrans in San Diego.

The chicks are about 3 weeks old now, Brimm said.

That they apparently are thriving above busy Harbor Drive and the Barrio Logan trolley terminal is testimony to how highly adaptable to urbanization the falcons are, he noted.

If the chicks can learn to fly without being hurt on the busy streets below, they might eventually become residents of ledges on downtown San Diego’s skyscrapers, Brimm predicted. That would treat downtown office workers to displays of falcons diving at up to 200 m.p.h. to catch pigeons in midair, as happens daily with a breeding pair that lives on the Union Bank in Los Angeles.

The birds are normally slate gray with a white throat and buff-colored breast, with wings that spread to upward of 3 3/4 feet.

The last instance of this endangered species nesting in the San Diego area occurred in 1948 and was photographed by Brimm, a longtime falcon watcher and a director of the Peregrine Fund. The private group has coordinated the release of about 3,000 peregrine falcons nationwide, 550 of them in California.

The California program has succeeded in establishing about 80 breeding pairs of the birds, most of them in the state’s central and northern regions. But Southern California has been problematic, apparently because of levels of chemicals in the birds’ food, Brimm said.

Toxic Chemicals

In the Channel Islands, for instance, dead embryos were found to contain high levels of toxic chemicals, including PCBs and dioxin, Brimm said.

It was chemical contamination of the eggs, which thins shells catastrophically, that decimated the nation’s peregrine falcon population in the 1960s. The main cause, DDT, has since been banned in the United States.

Brimm said he suspects that the San Diego chicks did not suffer chemical contamination problems because their parents’ main food source is bridge-dwelling pigeons, which tend to eat food that came from human sources, rather than from the wild. In the Channel Islands, falcons feed primarily on shore birds that ingest contaminants in the wild, he said.

The female in the San Diego pair was released from the cliffs on Point Loma in June, 1986, but was found injured and being assaulted by gulls on Pacific Beach five months later. The bird had suffered a severed muscle from flying into a wire, Brimm said. The bird was re-released by the group the next June and before this month was last seen in September, 1987. One reason she could be identified was a distinctive scar in one eye, the result of the gull attack.

Brimm said he and others have alerted residents and business people in the area under the bridge, in hopes that they will help assure that the three chicks are not injured, for instance, if they land on a busy street while learning to fly.

Return to Nest

Caltrans officials, who are holding a press conference today under the bridge, are currently delighted at the birds’ presence, but the birds eventually could create headaches. Federal law prohibits activities that interfere with endangered species, so Caltrans has suspended all maintenance and other activities on the section of the catwalk near the nest, Saville said.

Since peregrine falcons tend to return to the same nest site year after year, Caltrans can expect similar suspensions every year for as many as 16 weeks a year.

Peregrine falcon eggs hatch after about 33 days, then the chicks are in the nest another 42 days, biologist say. Then, they spend four to six weeks learning how to hunt from their parents before leaving to search for their own home range.