10/04/2022

Brink of Extinction: Climbers Help Bring Peregrine Falcons Back to El Capitan

This story first appeared in the winter 2011 Vertical Times.

By Sarah Stock, wildlife biologist, Yosemite National Park

Have you ever heard the rush of feathers when a peregrine “stoops” or dives from high above? Or witnessed a peregrine strike its prey in midair with a sharp blow? If so, you’re probably a climber, for peregrines are attracted to the same vertical landscapes. Clocked at more than 200 miles per hour, the peregrine has evolved to be the fastest animal in the world. Climbers and peregrines both push the boundaries of physical prowess and share an intimate knowledge of a mostly pristine realm. On more than one occasion, a climber has run up to me, full of excitement, to relay an amazing experience just shared with a peregrine. One time the climber finished his story by exclaiming, “You need to close that area!”

A peregrine falcon. © NPS.

Admiration for this raptor and awareness of its plight during the last few decades led to recovery efforts that, today, are regarded as among the most successful in the history of endangered species conservation. What drove peregrine falcons to the brink of extinction? Between about 1940 and 1970, a potent insecticide called dichlorodiphenyltrichloroethane (DDT) was used to reduce the threat of malaria and to protect crops from insect devastation. Hailed as a wonder invention, more than 1.3 billion pounds of DDT was applied in the U.S. before it was banned. As it turned out, this wonder invention was not only an extremely potent killer of insects, but it was also toxic to a wide range of animals, particularly predatory birds. By passing through the food chain, DDT became more concentrated in peregrine falcons than in most other animals in the same environment. By the 1970s, peregrines had disappeared completely east of the Mississippi River and were barely hanging on in the west, with only about 10% of the population remaining in California.

After a 16-year absence, peregrine falcons are nesting once again on El Capitan in Yosemite National Park.

Thankfully, legislation was on the peregrine’s side. In 1972, DDT was banned in the United States. In 1973, the peregrine falcon was listed as an endangered species under the newly established Endangered Species Act. Led by nonprofit groups such as the Peregrine Fund and the University of California Santa Cruz (UCSC) Predatory Bird Research Group, biologists, falconers, and climbers teamed up to save the species.

Climbers help recovery efforts

The National Park Service called upon the technical skill of climbers to reach the peregrines’ nests to examine possible causes of nest failure. Climbers invariably found that all that remained in the nests were thin eggshell fragments, which they collected for biologists to test. Biologists determined that high DDT levels in the birds were causing the eggshells to break and the embryos to die at an alarming rate, rapidly driving the birds toward extinction

Yosemite biologist Sarah Stock and Access Fund staff monitoring nesting activity on Elephant Rock. Ancestral lands of Southern Sierra Miwok, Northern Paiute, and Miwok. © NPS.

In an attempt to remedy the problem posed by eggshell thinning, climbers scaled the cliffs to access the nest sites, removed the DDT-laced eggs, and swapped them out with artificial “dummy” eggs for the adults to incubate. Then climbers helped swap out the dummy eggs with chicks that were safely hatched in laboratory conditions for the adults to brood and raise as their own. This was no easy task. “There’s nothing more terrifying than invading a peregrine’s nest … you look up to see the bird tucking its wings and coming at you flying over 100 mph only to flare off above your neck. They could easily take a climber out, but they don’t know this yet,” says longtime Yosemite climber Ken Yager. With climbers’ help, these captive breeding programs successfully released over 1,000 young peregrines back into the wild. The peregrine falcon was removed from the list of endangered and threatened species in August 1999. A decade later in 2009, the peregrine was removed from California’s endangered species list; however, peregrines remain a fully protected species in California.

After a 16-year absence, peregrine falcons are nesting once again on El Capitan in Yosemite National Park. The return of the peregrine to this iconic cliff symbolizes the recovery of a species that was once nose-diving toward extinction. Climbers have played an important role in this recovery and continue to play a key role in protecting peregrines by respecting seasonal closures and helping to monitor nests.

Yosemite’s temporary closures

Yosemite National Park represents the highest documented peregrine falcon nesting density in the Sierra Nevada. On several occasions, I have been asked why Yosemite protects peregrines when they seem to be versatile enough to nest in cities. Unlike cities, national parks are intended to conserve natural ecosystems. Thus, Yosemite takes a proactive approach to managing and protecting peregrines in their natural environment. Over the last three years, Yosemite biologists have been actively searching for and monitoring up to ten peregrine nests each season. To help the peregrines’ nests succeed, the park closes climbing routes that are directly adjacent to and within the immediate viewshed of the nesting pair during the critical nesting period (March 1 to August 1). The closures are set in place to prevent incidents that have happened in the past. For example, in 2002 the NPS instituted experimental voluntary climbing closures that were minimally respected, which most likely contributed to the nest failure on the Rostrum that year.

At the peak of closures, 97% of established climbing routes in Yosemite Valley are still open. And for seven months of the year, 100% of routes are open.

Active monitoring and temporary seasonal closures are a win-win situation for climbers, NPS management, and peregrines. Closures are implemented March 1 in areas where nesting occurred in the previous two years. During March, peregrine pairs are courting one another, strengthening their pair bonds, and selecting the most ideal ledge to raise their young. In mid-March, daily monitoring commences to determine where and when the birds will begin nesting. By mid-April, most of the breeding pairs are incubating eggs. April is a key month for narrowing down the climbing closures, i.e., lifting closures where there are no indications of breeding activity, and, in some cases, implementing new closures where peregrines have chosen an alternate or new nesting location. Around the first week of May, the eggs hatch; and the adults protect their nestlings from the elements (heat and cold stress) and potential predators, and keep them nourished with ample prey (e.g., swifts, robins, flickers, and pigeons).

Fledging usually occurs by the end of June when the young are about 42 days old. Closures remain in effect through August 1 to give the young a chance to learn how to fly and hunt on their own.

“This is an amazing success story, and it is my hope that climbers recognize the significance of the comeback that the peregrines have enjoyed in Yosemite.”

Throughout the closure period, as survey observations reveal new information, there may be several amendments to the closure notice. In 2010, the notice was revised twice, resulting in one closure lifted and one new closure implemented (at El Capitan). In 2011, the notice was revised three times, resulting in four closures lifted and no new closures. Each year is different. Some years are good reproductive years and other years are poor; and the closure amendments reflect the birds’ success. Working closely with biologists, Yosemite Climbing Ranger Jesse McGahey advises the specific route closures, communicates closure information to climbers (via online forums, information boards, notices at the base of climbs, coffee Sunday, and more), and enforces the closures.

Are seasonal closures too high a price to pay to protect and experience this amazing animal in its native habitat? While the closures are temporary for climbers, they have a lasting positive impact on peregrines. Says McGahey, “This is an amazing success story, and it is my hope that climbers recognize the significance of the comeback that the peregrines have enjoyed in Yosemite. Through the climbing community’s respect for this incredible bird, and their cooperation with the National Park Service, we have helped the peregrine soar again as it continues to recover from the brink of extinction.”

Even though I’m one of the people who implements and lifts the climbing closures in Yosemite, I’m looking forward to the day when the peregrine no longer needs specific protection and we no longer have to manage ourselves. In the meantime, we will continue to do all we can to make sure this bird is here to stay in its rightful place on El Capitan and the other famous cliffs in Yosemite.


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