Information for Birders
The Peregrine Falcon
The American peregrine falcon (Falco peregrinus anatum) was present in the United States at least 30,000 years ago. It bred in nearly every state in the Union. Threats to the peregrine were vastly increased after human population expansion in the last century. This adaptable species thrived for many decades despite extensive persecution by man. But in the early 1950s, the breeding population began an unprecedented and precipitous decline. In 1970, the peregrine falcon was listed as an endangered species. By the mid-1970s, only 20 percent of the breeding pairs remained.
There is evidence of a gradual decline of the peregrine in some regions prior to the DDT era, due perhaps to higher mean temperatures and lower precipitation. However, this decline was minor compared to the effects of DDT. DDT (dichlorodiphenyl trichloroethane), a chlorinated organic insecticide used in agriculture, caused eggshell thinning which led to poor reproductivity. Peregrines ingested DDT mainly from preying on migrant insectivorous birds. DDE, a metabolite of DDT, was present in amounts sufficient to account for pronounced shell thinning in peregrine eggs as early as 1948.
Prior to 1975, 23 peregrine nesting territories were known in Montana. By 1980, there were no known breeding peregrines in Montana. At this time, efforts were initiated to re-establish peregrines in Montana through the release of young birds produced in captivity. For Montana, these efforts started in the Centennial Valley, an ideal location because of its abundant cliffs and nearby bird populations.
When it was realized that the peregrine population was in grave danger, a plan was developed that called for the direct protection of peregrines and their habitat, action to increase natural reproductivity, and continuation of captive breeding and release. These three measures had emergency priority.
Advances made by The Peregrine Fund in the technology of artificial insemination and incubation made large-scale captive propagation of peregrines feasible. Natural reproduction was enhanced by artificial incubation of eggs and the return of those young to the wild. Young were raised in captivity until just before they could fly. They then were placed at a hack site or hack tower in the wild. They were fed by hack site attendants while they learned to fly and hunt for themselves, eventually becoming independent. This process is called "hacking out".
Red Rock Lakes and the Centennial Valley
In the late 1970s, peregrines were only sighted occasionally in the Centennial Valley. From 1981 to 1988, captive-reared birds were hacked out by The Peregrine Fund at up to three sites. In 1984, the first wild pair to return to Montana nested on a cliff in the Centennial Valley. These were birds released into the wild by The Peregrine Fund several years earlier. This pair has produced young every year since. In 1986, a second pair returned to a hack tower in the valley. One of these was hacked out in Colorado. In 1987, a third pair returned to another hack tower, and in 1988, a fourth pair returned to the valley. By 1989, all hack sites were being used by wild pairs, in addition to one natural site. Efforts to hack-out captive-reared birds were discontinued. Peregrine falcons are sited regularly, and there are now four confirmed breeding pairs in the Centennial Valley.
Peregrines formerly nested on cliffs, usually in mountainous areas or near rivers or lakes. In the Rocky Mountains, they now persist mainly on mountain cliffs and river gorges. Remaining aeries exist on dominant cliffs which generally exceed 200 feet in height. Nests are situated on open ledges or potholes. A preference for a southern exposure increases with latitude. Peregrines nested from the lowest elevations to above 9,000 feet. However, nesting above 8,500 feet is rare. In the Rockies, the majority of known remaining pairs are near ponderosa pine forest or pinyon-juniper woodland. Nest sites are often adjacent to water courses and impoundments because of the abundance of avian prey which frequent such areas.
In the Centennial Valley, pairs are usually present on the nesting site by late March. A clutch of three or four eggs are laid in late April. Incubation lasts 33 days. The young remain in the area several weeks after fledging in mid-July. During this time they are fed and defended by both adults.
Peregrines may travel up to 17 miles from nesting cliffs to hunting areas. Flight speed in excess of 60 miles an hour allow this falcon to hunt large areas with little effort. Preferred hunting habitats such as cropland, meadows, river bottoms, marshes, and lakes attract abundant bird life. Peregrines appear to capture a wide variety of birds, including blackbirds, jays, doves, shorebirds, and smaller songbirds. Most prey species are struck from above at great speed, but they often evade the falcons attack by aerobatics or diving to cover.
Annual juvenile mortality is estimated at approximately 55 to 70 percent and adult mortality at 20 to 30 percent. The mean life expectancy for those young that fledge is probably near four years. The recorded maximum life span is in excess of 13 years, though it is not unreasonable to assume that a few individuals may live to 20 years since several peregrines reached that age in captivity.
Human-caused mortalities that have been documented include shooting, poisoning, pole-trapping, destruction of nestlings, egg collecting, and interference at the nest causing abandonment or fatal interruption of parental care. A variety of predators have been known to prey on peregrines or their eggs, including great horned owls, prairie falcons, raccoons, coyotes, foxes, golden eagles, ravens, crows, striped skunks, bobcats, and possibly ospreys. Accidents account for some peregrine mortalities. These include collisions with powerlines, fences, automobiles, and airplanes, falling and being blown from nests, rock slides, aerie sloughing, electrocution, and drowning. At least ten diseases and parasites are known from wild peregrines. Peregrine deaths from botulism, herpes virus, pericarditis, leucocytozoonsis, and pneumonia have been reported.
Peregrines do not normally breed until at least two years old. They must fledge approximately 1.25 young per pair in order to sustain the population. Due to long average life expectancy and the peregrines population dynamics, successful management operations do not provide quick population recovery.
On August 25, 1999, the U.S. Fish and Wildlife Service officially removed the American peregrine falcon from the Federal List of Endangered and Threatened Wildlife, recognizing the subspecies' recovery following restrictions on organochlorine pesticides in the United States and Canada, and following the implementation of successful management activities. Although delisting the peregrine removes it from the ESA's protection, it still will be protected by the Migratory Bird Treaty Act, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, and state laws and regulations; and its status will be monitored for a minimum of five years. If during this period it is determined that the peregrine again needs the Endangered Species Act's protection, the Fish and Wildlife Service would relist the species. In response to the successful recovery of the peregrine falcon, the Peregrine Fund's last release of captive-bred peregrine falcons was in 1997. For information on recent peregrine falcon production in the Centennial Valley and Montana, visit the Threatened and Endangered Species section of the Refuge Management webpage.
Our sincere thanks and congratulation to all the staff, volunteers, and supporters of The Peregrine Fund who have helped make the peregrines return to the Centennial Valley a success.
(Excerpts from The Peregrine Funds annual Operations Report, and Peregrine falcon productivity in the Greater Yellowstone Ecosystem, 1988, by Ed Levine.)