Project- Peregrine Falcon

Understanding Tundra Peregrine Falcon
Migration Patterns and Population Trends

Click Here for Species Description of Peregrine Falcon

Problem/Background

Peregrine Falcons (Falco peregrinus) once had very stable populations in most regions of the world.  After World War II, their populations began to decline drastically in many parts of the world.  Prior to the 1940s, there were approximately 7000 Peregrines in North America.  By the 1970s, there were only a few hundred.  Historically, there were 300 active Peregrine nests in the eastern United States, but in 1963, not a single nest was active. It was then discovered that Peregrines had disappeared entirely from the eastern third of North America.  Biologists and scientists found that the organochlorine known as DDT (dichlorodiphenyl-trichloroethane), a popular insecticide used after World War II, was at least partly responsible for the decline.  DDT disrupts the reproductive system of female birds, and may prevent birds from laying any eggs at all. The eggs that were produced had extremely thin and weak shells, because DDT interferes with the bird’s ability to produce calcium for egg production.  Eggs with such thin shells cracked when the female tried to incubate them.  For many years, hardly any Peregrines were able to produce young.  Even the Tundra Peregrine Falcon (Falco pergrinus tundrius), which breeds north of the Arctic Circle, showed very large population declines.  Although the banning of DDT along with the development of Peregrine recovery programs have helped increase Peregrine Falcon populations, it is still very important to monitor these populations and to determine what other factors still threaten them.

Objectives and Methods

In order to help protect Peregrine Falcons, scientists need to know where migrating Peregrines spend the winter, breed, and stop over to rest during migration.  They also need long-term data showing how the numbers of Peregrines in North America have changed over the years.  Scientists from the Center for Conservation Research and Technology (CCRT) and Earthspan used satellite transmitters to track the movements of these birds.  Starting in the autumn of 1993 and continuing through 2000, the Earthspan scientists applied dozens of transmitters to migrating Tundra Peregrine Falcons along traditional Tundra Peregrine migration routes.  These areas include the coasts of Maryland and Virginia (Assateague Island), the gulf coast of Texas (Padre Island) and Mexico, Greenland, and Eastern Canada.  The team of scientists also monitored the numbers of Peregrines returning to these areas year after year by trapping the birds on migration and placing leg bands on thousands of birds.  The leg bands allow scientists to individually identify each bird, and they can tell if the same bird returns year after year. 

Results/Conclusion

The long-term monitoring of Peregrine Falcons in Greenland, Assateague Island, and Padre Island has resulted in the marking of over 15,000 individuals.  The CCRT and Earthspan scientists documented the migratory population trends for this species over the past three decades.  In addition, they have continuous data on Peregrines on Assateague Island starting from 1938, when the North American falconer and naturalist, Alva Nye began to monitor them.  This project is the longest running continuous survey of Peregrine Falcons in North America.  In Greenland, the scientists studied the population dynamics of the Peregrine, as well as many aspects of their behavior on the breeding grounds.  During the 1980’s they found an actual increase in the density of nesting pairs of Peregrine Falcons in their 3,000 square mile study area.

 

Information from the use of satellite transmitters contributed significantly to understanding the recovery of the Tundra Peregrine in North America.  In only a few years, these transmitters have provided more data of Peregrine Falcon migratory patterns than the past 25 years of conventional field studies.  Scientists are now learning exactly where these birds travel, where they stop along their trek, and what threats may exist to their survival along the way.  The use of satellite tracking has proven to be an important tool for the conservation of migrating species.