Cliff-dwelling birds typically have it pretty good. Cliffs serve as a physical barrier, protecting birds from terrestrial predators as well as human disturbances. Cliffs also provide ample nesting sites, and the high-altitude can allow birds to spot potential threats as they approach from below. As climate change becomes an increasing threat to many species, leading to temperature changes and more frequent and intense weather events, cliffs will likely provide important refuge from storms.
“There is a reason many birds of prey seek out cliffs for nesting — to keep away from predators so that they can safely raise their young without interference,” explains Jordan Rutter, Director of Public Relations for the American Bird Conservancy.
Yet there’s one thing that may pose a unique threat to these elusive birds: rock climbers.
For the same reasons that cliff habitats are advantageous to birds, they are understudied by humans. Cliffs are difficult for researchers to access to monitor bird behavior. Advances in wildlife cameras have allowed researchers to gain a deeper snapshot into the behaviors of cliff-dwelling birds, but much is still unknown.
That includes a full picture of the effects of rock climbers on bird behavior.
“There may be situations where disturbance by rock climbers is very important,” says Tim Meehan, a quantitative ecologist for National Audubon Society and climbing wildlife biologist, noting that climbing generally is not seen as posing the same magnitude of threat as other factors like climate change, habitat loss, and collisions with human structures. “Imagine a region where cliffs and cliff-nesting birds are very rare, where the few cliffs are beloved by climbers and the few birds are beloved by birders. In this situation, the birds might be constantly disturbed by people, to the point where the birds are stressed out and flighty, predators come and go at will, nests fail, cliffs are abandoned by birds, there are few alternative nesting sites, and local populations decline.”
Rock climbing appears to be on the rise in the United States. In 2017, over 2.5 million Americans engaged in traditional, ice, or mountaineering climbing, up from 2 million in 2007, according to a report by the Outdoor Industry Association. Even more Americans, an estimated 5 million, engaged in indoor climbing that year, which could spark an interest in outdoor rock climbing.
The sport first rose in popularity in the United States after World War II. In the post-war home front, Americans flocked to nature as they celebrated a time of peace and escaped increased urbanization. Nylon was also discovered in the 1930s and used by military to make stronger ropes for soldiers scaling mountain ranges. After the war, rock climbers began using nylon and carabiners found in army surplus stores which made climbing safer and more accessible.
Recreational rock climbing began at Joshua Tree National Park in the 1940s and expanded from there. The first study to examine the effect of rock climbers on bird communities took place within the park as well, in 1998. Researchers found that birds living on unclimbed cliffs were more likely to be perched on them, while birds at popular climbing cliffs were more likely to be flying around the cliffs. Around 29 percent of birds were seen flying at popular cliffs, compared to 4 percent at unclimbed cliffs. The research suggests that the birds were spending more time flying in order to avoid humans disturbances, the authors wrote, which could result in disrupted breeding, foraging, and predator detection behaviors.
A 2004 study also indicates that climbers could be having an impact, finding that the presence of rock climbers decreased the reproductive success of peregrine falcons in Italy and Switzerland. Breeding success was found to be lower on cliffs with rock climbers compared to undisturbed cliffs. The lowest breeding success was found on cliffs with both rock climbers and ravens. Researchers believe that the presence of rock climbers scared peregrine falcons away from their nesting site, leaving their young unprotected from predators. Ravens, who have a higher tolerance for human disturbance, took the opportunity to snatch the young.
Rock climbing does not affect all bird species equally. Peregrine falcons are sensitive to human disturbance and may abandon their nest as a result of rock climber presence. Notably, rock climbing is listed as a threat to the species in its IUCN Red List Assessment. On the other hand, research suggests that other species may be tolerant to human disturbance. A 2019 study, for example, found white-throated swifts common at both high and low-use climbing sites.
To protect birds from human disturbance, park officials routinely close off sections of cliffs from rock climbing activities during breeding season, but monitoring nesting activity can be a difficult and time-intensive task.
“Common factors that impact the ability for land managers to properly assess cliffs is often staff time and resources,” says Katie Goodwin, policy analyst at the Access Fund, a not-for-profit organization which advocates for keeping climbing areas open in the US and conserving climbing environments. “Often land managers state that they do not have the staff resources, time, budget, ect. to conduct active monitoring throughout the nesting season. As a result they issue large blanket closures that are not founded on active monitoring data.”
Nesting and fledgling seasons often occur in the spring and summer which is a popular rock climbing time. While precautionary closures of wide swatches of cliffs may be beneficial for nesting birds, some rock climbers see it as overly restrictive and unnecessary. And some frustrated climbers sometimes ignore the closures.
“Even in areas that are considered protected, such as national parks or national forests, enforcement of rules over large areas is not always possible. Climbers and other outdoor recreationists need to understand how important self-restraint and awareness can be to helping wildlife coexist with people,” explains Rutter.
In the United States, some national parks have begun implementing adaptive management plans to balance bird conservation efforts with the ability of humans to enjoy public lands. In Zion National Park, all climbing routes used by nesting peregrine falcons are closed on March 1 each year. Biologists monitor the nesting activities of birds and will re-open sites that are not being utilized by birds. Sites that are used for nesting will be re-opened after chicks fledge.
The relationship between rock climbers and cliff-dwelling birds does not need to be a fraught one. To the contrary, rock climbers are able to traverse hard-to-access habitats and could be a valuable resource for bird conservation projects.
In fact, they were instrumental in saving peregrine falcons from the brink of extinction. In the 1940s, peregrine falcon populations began plummeting due to exposure to the insecticide dichlorodiphenyltrichloroethane, also known as DDT, exposure to which caused raptors, including peregrine falcons, to lay eggs to have thinner shells. The shells were more likely to break, which led to plummeting population numbers for several species.
By the 1980s, biologists developed a project to swap out eggs exposed to DDT from peregrine falcon nests so that the chicks could be safely hatched. They would replace the falcon eggs with wooden eggs for the duration of the nesting season, and then later those eggs would be replaced with captively-raised chicks. Biologists recruited rock climbers to swap out the eggs, according to Outside.
DDT has now been banned in the United States for decades but climbers still collaborate with researchers to help conservation efforts. The Access Fund currently works with land managers and local climbing groups to establish volunteer monitoring and citizen scientist programs. In Zion National Park, local climbers help fill the void in staff time and resources by assisting in peregrine falcon nesting surveys. Thanks to the collaborative efforts, Zion was able to reopen seven cliffs in 2019. These efforts help to alleviate feelings of frustration among rock climbers related to cliff closures, and provide much needed resources to land managers.
“Most climbers support wildlife conservation, and their participation in monitoring efforts, thoughtful closure design, and faithful closure enforcement, helps them reconcile their support for conservation with their love of climbing,” Meehan explains.