By James Hale;
Captive breeding programs have led to the falcons’ recovery
The Peregrine Falcon (Falco peregrinus) is a large cosmopolitan falcon with superior hunting skills capable of flight exceeding 240 miles per hour. The scientific name peregrinus is Latin for wandering, in reference to its worldwide range. The insidious effects of DDT, a chlorinated hydrocarbon, from 1940s to the 1970s had significant negative impacts on nesting falcons. Bald Eagles, Osprey, Brown Pelicans and other top predator species experienced similar effects from the substance known as DDE, a metabolite of DDT that was produced in the birds’ bodies. DDE became concentrated within food chains causing these species to lay eggs so thin shelled that they broke or otherwise failed to hatch. By 1970, researchers knew of only two breeding pairs in California, down from several hundred pairs some 20 years before.
The ban on DDT in North America in 1972, followed by intensive conservation and reintroduction efforts, Â have brought about a strong and heartening recovery for all of these species across much of their ranges.
All three races of Peregrine Falcons occur in California. Peale‘ s Peregrine, the Tundra and Anatum races differ mainly in the degree and extent of their markings and coloration. The Anatum race is most commonly seen in California. The adult Anatum’s head is blackish, with a broad malar eye stripe over a buffy cheek. The belly is often buffy to nearly salmon colored. Juvenile birds are lighter colored, have conspicuous streaking of the under-parts, and appear to be long tailed. They reach sexual maturity at 2-3 years of age. The sexes generally look alike, but the male is 30% smaller and less heavily marked ventrally. The different sizes between the sexes, known assexual dimorphisim, allows the pair of falcons to take a wider variety of prey. During the spring breeding season, Peregrines are quite vocal when “echup”calls are exchanged between partners and the throaty “kak-kak-kak” notes announce the presence of a predator.
The Peregrine is specialized for catching birds, more than any other raptor. It is able to scan the sky for over a mile from a perch for prey or may use speculative flights, taking advantage of the contours of the land hoping to startle a bird into the air. The Peregrine Falcon is most noted for its attacks from a high flight or soar. The celebrated stoop and meteorlike plunge downwards with speeds in excess of 240 miles per hour are spectacular. Birds are the chief prey, although bats and insects are sometimes taken.
Peregrines essentially catch what is locally available. At metropolitan eyries, pigeons and starlings are readily available. I have rescued dazed and injured Peregrines that have struck high rise buildings glass windows as they pursued pigeons in Oakland and San Francisco. Along coastal cliffs and around the bay, shorebirds are favored. A variety of other birds including meadowlarks, wrens, cormorants and geese constitute the Peregrines diet. Nest cliffs consist of a scrape or depression, fashioned by both partners, high on a ledge where the three or four reddish brown eggs are laid. The pointed end of the eggs keep them from rolling off. Incubation by both parents is over the next 33-35 days. After hatching, the young remain on the nest ledge for about 42 days before launching their inaugural flight. The Coastal Ranges foothills have the highest populations, although every bridge in the San Francisco Bay Area, the TransAmerica highrise, and El Capitan in Yosemite have nesting Peregrines. On the Channel Islands, sometimes this species nests on the ground in gull colonies. Sea-stacks, rock pinnacles, tree hollows and other birds nest have been used for nesting as well. Locally, cliffs on Mt. Diablo have historically and presently support breeding Peregrine Falcons.
The state of California listed the Peregrine Falcon as an endangered species in 1971; the federal government listed it soon afterward. In 1975, my friends Brian Walton and Jim Rousch, wildlife experts at the University of California at Santa Cruz, established the Santa Cruz Predatory Bird Research Group (SCPBRG). Through captive rearing programs in the laboratory, cross-fostering with Prairie Falcons, hacking and other techniques, the Peregrine Falcon recovery program took flight. Between 1981 and 1992 the Santa Cruz group successfully raised close to 400 birds for release back into the wild. By the end of 1992, the SCPBRG, working with federal and state agencies, had released nearly 800 captive-bred falcons, mainly in California but also in Oregon, Washington, and Nevada. By the spring of 1992, the number of wild breeding pairs of Peregrines in California had surpassed the goal of 120 pairs set by the U.S. Fish and Wildlife Service. Today more than 300 pairs nest in the state.
Even with past and present conservation efforts, the stability of Peregrine Falcon populations is at risk. The birds remain vulnerable to chemical contamination from several sources. Migratory neotropical birds that winter in Central and South America, where DDT is still used, return as potential Peregrine prey with DDT concentrated in their bodies. Residual deposits of DDT persist throughout the ecosystem. As a result, in many parts of California, Peregrines continue to lay eggs as thin shelled as in the 1950s.
Without local, regional, and global preservation, conservation and management programs, the future of the stateÊ¼ s Peregrine Falcon population is uncertain.
James M. Hale is a wildlife biologist, and is Vice Chair of the Contra Costa County Fish and Wildlife Committee.