Peregrine Falcons: On the road to recovery
The peregrine is the world’s fastest bird; it can reach over 200 miles as it dives from tall cliffs onto smaller birds (1). It circles high searching for prey and when a smaller bird like a pigeon takes off it plummets to the earth and kills it with razor sharp talons. The Peregrine’s identifying characteristics include its large size, long pointed wings and dark mustache set against white cheeks (11). The female has a wingspan of about 4 feet and often weights more than two pounds as compared to the smaller males the generally only weight in at one pound (11). It was found from the subarctic boreal forests of Alaska and Canada all the way south to Mexico (1). It was called ‘the worlds most successful flying bird’ largely as a result of its unsurpassed flight characteristics and unusually stable, near-global population. Peregrines could once be found on every continent except Antarctica (2). Besides man the Peregrines only natural predator is the great horned owl which often raids the Peregrines nest (11).
The peregrine has recovered remarkably well. It is now found throughout North America and is breeding in the wild. There are 1,593 breeding pairs of Peregrines in North America, up from 324 in 1975 and well past the initial repopulation goal of 631 pairs (3). Their repopulation was aided by their integration into manmade environments. Peregrines have adapted remarkably well to the city environment. Often they make nests on the ledges of sky scrappers where they are able to dive down onto the unsuspecting pigeons that cloud the city air. They will return to the same ledge year after year. Over 50 pairs of Peregrines winter in L.A. (4).
DDT was a very effective and stable pesticide that was sprayed over large sections of swampland in order to combat mosquito populations. Because of its stability it was concentrated as it moved up the food chain. It kills mosquitoes and other small insects that are then eaten by fish which in turn are eaten by birds of prey. When DDT is introduced into the environment it produces DDE, which accumulates in eggshells causing them to break in the nest (2). The Environmental Protection Agency banned the pesticide in 1972. One of the major driving forces behind the banning of DDT was the book “Silent Spring” by Rachel Carson, who was a former U.S. Fish and Wildlife employee (3).
Peregrines are often brought into shelters after being wounded by hunters. In past years they were killed because they feed off of game birds such as quail. The Migratory Bird Treaty Act states that it is illegal to trap, kill, or otherwise disturb the Peregrine and it’s nests. DDT and its effects decimated a once healthy peregrine falcon population. Populations in the western states dropped more than 90% (3). In 1970 there were only two pairs in all of California, down from an estimated 300 in 1960 (2).
The population was helped along the road to recovery by the banning of DDT. Despite this action large amounts of the chemical lingered in the environment for years to come. The peregrine was put on the endangered species list in 1973(2). This is one of the reasons for its rapid increase. There was a massive captive breeding effort and over 6,200 pairs were released into the wild (4). Mostly volunteers and zoos hand raised these falcons. This breeding effort was instrumental in repopulating the Peregrine to the wild. One problem with a captive breeding program is the possibility of a founding effect and population bottleneck. Also many non-innate behaviors, normally taught by the parents, captive hatchlings do not know. Often times eggs from captive breed birds would be placed in wild Peregrine nests. The success of the Peregrine has become an important symbol for the Endangered Species List and the US Fish and Wildlife. Its success means that it is possible to repopulate a species into the wild.
Controversy still surrounds the Peregrine even in the midst of its amazing rebound. The numbers of Peregrine pairs in the wild are much higher than the original goals of the repopulation programs. As mentioned earlier, in 1970 there were only 2 peregrine pairs left in California, in 1997 there were 125 pairs (2). As a result of the overall increase in Peregrine population, on August 25, 1999 it was taken off the endangered species list (1). This move was harshly criticized by some of the scientists who were instrumental in the falcons return to the wild. Even though the population has increased dramatically, little has been done to protect the habitat of the birds and the loss of genetic variability remains a major concern. The large increase in peregrine population is largely the result of captive birds being released and as a result it is believed that there may be a population bottleneck and a loss of genetic variability. For the most part the Peregrine’s population has expanded, but the genetic variability of the species remains undetermined. For the most part however, the Peregrine still stands as one of the few successful attempts to reverse the consequences of mans interference in the natural cycle of life.