Yosemite’s Peregrine Falcons Are Thriving with Unexpected Help from Rock Climbers

After pesticides severely reduced their numbers, peregrine falcons are making a comeback in Yosemite National Park, thanks in part to an unexpected partnership with rock climbers.

Historically, peregrine falcons, which nest on the sheer granite cliffs of Yosemite, faced disturbance from climbing activities. Rock climbing is listed as a potential threat to the species, as the presence of climbers can disrupt nesting. However, climbers and conservationists have worked together in a unique collaboration that has supported the recovery of the falcons after decades of decline.

According to a recent update from the National Park Service and the Yosemite Conservancy, the peregrine falcon population in the park has shown significant improvement. As of spring 2024, naturalists documented 17 breeding pairs—a 113 percent increase from the eight pairs in 2009. There were also 15 nests and 25 chicks reported. Since 2009, 51 nesting sites in Yosemite have produced 385 chicks.

“Peregrines are at the top of the food chain and highly susceptible to environmental contamination,” says Frank Dean, president of Yosemite Conservancy. “Their recovery is a positive indicator of the overall health of the Yosemite ecosystem.”

Peregrine falcons, known as the world’s fastest animals, can reach speeds of up to 200 miles per hour in their hunting dives. They are found on every continent except Antarctica, nesting on rocky cliffs.

After World War II, the use of pesticides such as DDT, dieldrin, and aldrin led to a dramatic decline in peregrine falcon populations. Dieldrin and aldrin were directly toxic, while DDT caused thinning of eggshells, reducing chick survival rates. By 1974, only 324 peregrine pairs were left in the U.S., down from more than 3,800 pairs before the mid-20th century. The species was listed as endangered federally in 1970 and in California in 1971. In Yosemite, peregrines were last seen in 1941.

The ban on DDT in 1972, followed by restrictions on aldrin and dieldrin in 1974 (and a complete ban in 1987), marked the beginning of the recovery for many affected species. In 1978, climbers Dale Bard, Hugh Burton, Bruce Hawkins, and Ron Kauk discovered an active peregrine falcon nest on Yosemite’s El Capitan. They reported their find to conservationists, who then developed a recovery plan involving the climbers.

The Santa Cruz Predatory Bird Research Group, with assistance from climbers, collected and incubated falcon eggs in a lab, returning the hatched chicks to their nests. Despite the risk of falcon attacks—one even struck a climber’s backpack—these efforts were crucial for the birds’ recovery. Ken Yager, a climber involved in the project, recounted the intense experience of being dive-bombed by falcons while handling the eggs.

For the past 15 years, climbers and the park service have worked together through the Peregrine Falcon Protection Program. This program includes temporary climbing route closures from March to July to protect nesting falcons and buffer zones to prevent disturbances from helicopters. Park staff monitor nesting sites and manage closures to ensure that over 95 percent of climbing routes remain open.

Human activities can disrupt wildlife behavior, including that of peregrine falcons, which might leave nests to fend off perceived threats, making eggs and chicks more vulnerable to predators.

Peregrine falcons were removed from the endangered species list in 1999. Estimates suggest that up to 40,000 peregrines now inhabit North America, and globally, their numbers may reach around 340,000. The International Union for Conservation of Nature classifies them as a species of “least concern,” indicating their populations are stable and increasing.

The cooperation between climbers and conservationists has been crucial to the peregrine falcon’s recovery in Yosemite. Alexandria Walker, a biological science technician at the park, describes this collaboration as a “remarkable comeback,” demonstrating the success of prioritizing conservation efforts.