Peregrines Offer a Great Measure of Species Recovery

Photo: Young Peregrine Falcon on a Metal Structure

One of four young peregrines near the top of the agricultural building where they fledged.

Four white and grey fluff balls with spindly yellow legs snuggled in their nest on a ledge beneath the Richardson Bay Bridge–not exactly a safe place for peregrine falcons to fledge with water 40 feet below. So the chicks got a little help this year thanks to the California Raptor Center (CRC) and the UC Santa Cruz Predatory Bird Research Group (SCPBRG).

After seeing many fledglings drown in the waters below the bridge over the years, Glenn Stewart, director of the SCPBRG, wrangled permission from US Fish and Wildlife Service to collect the birds at about three weeks of age and transfer them to the CRC–a program of the UC Davis School of Veterinary Medicine. The chicks were fed and cared for at the CRC for a week before being moved to the top of a building at an agricultural location on the edge of campus where they could complete fledging and begin to experiment with flight.

"I may be a relic from the population recovery days, but I cannot abide seeing peregrines pitch off into the sea if I can do something about it," Stewart said. "We have the ability to facilitate a transition to wild independence that is 99 percent better than the chance they had at the Richardson Bay Bridge–so why not do it?"

This is the second year that the CRC has collaborated with the Santa Cruz group to care for rescued peregrines until they are ready to be independent, typically at about 65 days old. While peregrines start flying at 43 to 44 days old, they don't start hunting on their own for about three more weeks, after they've become efficient aerial attack machines. They've been clocked at more than 200 mph and are considered the fastest animal on earth.

"When we received the birds, they were too young to be placed directly into the hack box so we kept them at the CRC in a box that is similar to the hack box at the release site," explained Bret Stedman, manager of the CRC. "We fed them through a small opening so they could not see us and associate humans with food."

Two days after their hack box had been opened atop the metal building on the outskirts of the UC Davis campus, Michelle Hawkins, director of the CRC, scanned the skies overhead for any sign of the newly fledged falcons.

"There, there, can you see it?" Hawkins exclaimed as one of the birds came flying back to its eyrie with a crow in hot pursuit. "This is fantastic! We want to see them out and about, moving out from home base and then coming back to eat."

During their transition to complete independence, the falcons have the instincts to catch wild birds for food but it will take them a few weeks to master the hunting skills they need for survival, according to Stedman. So until the young falcons can forage successfully on their own, CRC staff and volunteers will come out to climb the metal stairs and toss previously frozen quail close to the hack box daily. During the time after they've fledged and before they hunt independently, temporary radio transmitters attached to one of their legs helps the researchers track the birds and determine how far from the hack box they are flying. The birds are also outfitted with a US Fish and Wildlife Service band and a colored band from SCPBRG.

While peregrine falcons have made an amazing comeback from the Endangered Species List, Stewart said he stills feels a responsibility to help the species thrive and to continue to increase the genetic diversity of the wild population. Because raptors and especially peregrine falcons exist at the top of food chains, regular surveys of their population can reveal threats to environmental health before they become hazards to human beings. The continued study of the peregrine falcon and its breeding status are important indicators of ecosystem health.

"I've got a soft spot for peregrines," he said. "We thought we were witnessing their extinction in the mid-70s. There are so many more now, it's unbelievable."

The peregrine's recovery in California is thanks to collaborative efforts of dedicated individuals, the UC Santa Cruz Predatory Bird Research Group, and state and federal agencies. As one of the first birds to be placed on California's Endangered Species List, the peregrine's dramatic decline was blamed on ingesting prey contaminated by DDT, which greatly weakened the birds' egg-shells, resulting in the eggs being crushed during incubation. The banning of this insecticide led to the species' recovery and the ultimate removal of the peregrine falcon from the Federal List of Endangered Species in 2009.

"Every wild born peregrine that achieves mating success will add to the genetic diversity of the species in California," Hawkins said. "And that's a great measure of species recovery."

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