In 1974, more than 6,000 peregrine falcons were released into the wild after the population wiped out; helping restore the once-endangered birds across North America | World News

In the early 1974s, American peregrine falcons were struggling to survive in parts of North America. Years of DDT use had left many eggs with thin shells that could crack during incubation, leaving fewer chicks to hatch. Conservationists responded by breeding the birds in captivity and releasing them into the wild. According to the National Park Service (NPS), more than 6,000 American peregrines were released through recovery programmes. Restrictions on DDT and legal protection also played a part in the comeback. Along Alaska’s rivers, long-term surveys later recorded a rise in nesting pairs. The American peregrine falcon was removed from the US federal endangered and threatened species list in 1999.

Peregrine falcon subspecies faced different levels of pesticide risk

The decline of peregrine falcons was closely associated with the use of DDT, an insecticide that became widespread during the mid-20th century. As the chemical passed through food chains, residues accumulated in birds of prey. Its breakdown product, DDE, interfered with eggshell formation, leaving eggs too fragile to withstand the weight of an incubating adult. Fewer chicks survived to hatch, putting pressure on populations that were already struggling.By 1970, the American and Arctic subspecies of peregrine falcon had been listed as endangered under the Endangered Species Conservation Act of 1969. Peale’s peregrines, found along parts of the Pacific coast, were not listed because their breeding populations had remained comparatively stable and exposure to DDT was limited.

Restrictions on DDT changed the course of recovery

The United States Environmental Protection Agency (EPA) banned DDT for most uses in the country in 1972, using powers granted under the Federal Insecticide, Fungicide, and Rodenticide Act. The restriction followed growing evidence of the damage the chemical was causing to wildlife, particularly birds whose survival depended on successful breeding.The change did not remove every source of exposure. DDE residues continued to be detected in some areas, while peregrines travelling to wintering grounds in Latin America could encounter pesticides that remained in use there. Even so, reducing DDT use in the United States helped create better conditions for the birds to reproduce.Legal protection and pesticide restrictions were accompanied by a coordinated recovery programme. The US Fish and Wildlife Service brought together federal and state agencies, independent biologists and conservation organisations to identify measures that could restore declining populations.

Captive-bred birds helped rebuild depleted populations

Scientists at Cornell University developed successful methods for breeding and raising peregrine falcons in captivity. The young birds could then be introduced into suitable habitats through a technique known as hacking, which gives them time to adjust to their surroundings before becoming independent.For the releases, young falcons were placed in specially designed boxes positioned on towers or cliff ledges. Food was supplied through a chute during the early stages, limiting the birds’ contact with people. Once they were old enough, the boxes were opened and the young falcons could begin exploring the area and exercising their wings.Food was gradually reduced as the birds developed their flying and hunting abilities. The intention was to give them a chance to establish themselves in the wild rather than remain dependent on human care.The programme involved the US Fish and Wildlife Service, state wildlife agencies, The Peregrine Fund, the Santa Cruz Predatory Bird Research Group and the Midwestern Peregrine Falcon Restoration Project. Together, these efforts resulted in the release of more than 6,000 American peregrines from 1974 onwards.

Arctic peregrines recovered without captive releases

The Arctic peregrine population had fallen by as much as 80%, but enough birds survived that captive-bred releases were not considered necessary for its recovery.Restrictions on DDT and protection under the Endangered Species Act helped numbers increase. In 1984, the Arctic subspecies was moved from endangered to threatened status, reflecting an improvement in its prospects. A decade later, in October 1994, the US Fish and Wildlife Service announced that the population had recovered sufficiently for the subspecies to be removed from the federal list of threatened and endangered species.Thousands of Arctic peregrines now occur across North America. Their recovery also demonstrated that populations could rebound when the pressures responsible for their decline were reduced, even without the extensive release programmes used for American peregrines.

Surveys along Alaska’s rivers track the return

In Alaska’s Yukon-Charley Rivers National Preserve, biologists have monitored peregrine falcons since the mid-1970s. During an early survey in 1975, they recorded 11 nesting pairs. More recent surveys in comparable areas have documented more than 50 to 60 pairs, providing a long-term indication of how the population has changed.The work involves searching cliffs and bluffs where peregrines establish nests, observing birds and recording their breeding activity. The terrain can make surveys demanding, but repeated visits allow scientists to compare nesting activity across years and assess whether birds continue to occupy established territories.The American peregrine falcon was removed from the federal endangered and threatened species list in August 1999. The decision followed a substantial recovery attributed to pesticide restrictions, legal protection and the release of captive-bred birds.

Monitoring continued after federal protection ended

Delisting did not mean that monitoring stopped. The US Fish and Wildlife Service established a schedule of post-delisting checks to determine whether populations remained stable after federal protection was withdrawn. Surveys were carried out in 2003, with further monitoring planned for 2006, 2009, 2012 and 2015.Results from the 2003 assessment estimated about 3,000 breeding pairs across the United States, Canada and Mexico. Researchers also examined territory occupancy, nesting success and productivity, measures that help show whether birds are reproducing successfully rather than simply appearing in greater numbers.