A peregrine falcon takes off from the beach at Assateague Island National Seashore. NPS
The peregrine falcon (Falco peregrinus) is the fastest animal there is: in a dive it tops 200 mph. It is a large falcon, with a 3.5-foot wingspan, and — as in other raptors — females grow bigger than males.
Telling them apart
| Plumage | |
|---|---|
| Juveniles | varies from lightly to heavily and darkly marked, with a dark brown cap — but always some shade of tan or brown |
| Adults | dark gray upper wings and crown, a distinctive dark "mustache" by the beak, and evenly gray-and-white underwings |
Where they live
Peregrines are found on every continent except Antarctica. They like to nest on cliffs and ledges, but will use transmission towers, skyscrapers and bridges. They eat mainly birds — at least 450 species have been recorded as prey. Some populations stay put; others migrate up to 15,000 miles a year to winter somewhere warmer.
Many tundra peregrines fly straight over Assateague Island on their way south. They rarely nest on the barrier island, but its quiet beaches and wide coastal dunes make an ideal rest stop in fall — and an ideal place for long-term research.
Decline and the survey
After World War II, widespread use of the pesticide DDT sent peregrine numbers crashing. The chemical built up in prey and then in the falcons, causing reproductive problems including thin eggshells. In 1970 the peregrine was federally listed as endangered.
As part of the renewed conservation effort, the Department of the Army started a research program to develop technology for monitoring highly migratory wildlife, and researchers set up a yearly peregrine survey at Assateague Island National Seashore — nearly 50 years ago.
Biologists process a peregrine falcon. NPS
Each survey records every raptor seen — species, time, place and what it was doing. Peregrines that can be reached are captured, banded, processed to current protocols and released. About 20,000 peregrines have been counted, and 5,746 captured for research. The program has since grown to cover contaminants, emerging pathogens and genetics.
A peregrine falcon is released after being caught and processed. NPS
Mercury
As tertiary consumers, raptors are exposed to biomagnification: pollutants concentrate as they move up the food chain. A study of feathers collected from Assateague peregrines during fall migrations from 2009 to 2015 found that mean total mercury in adults had risen from 4.45 mg/g historically to just over 10 mg/g.
Recovery
| Year | |
|---|---|
| 1970 | listed as endangered |
| 1994 | the migratory tundra peregrine (F. p. tundrius) — the subspecies studied at Assateague — removed from the endangered list |
| 1999 | the continental peregrine (F. p. anatum) removed too |
Survey data from Assateague show the population has rebounded. Over the last decade, though, slightly fewer falcons have been seen there. Researchers suspect:
- more severe weather;
- more people and development along the coast;
- more bald eagles on Assateague's beaches — eagles are aggressive toward peregrines, which may be choosing safer shores elsewhere.
That isn't necessarily cause for concern: populations are stable across the region.
Why it matters
The Assateague study is now one of the longest-running peregrine studies in the Americas, and it shows how important barrier islands are as habitat for rare species along the Atlantic Flyway.
Sources
Based on "Northeast Coastal and Barrier Network Species Spotlight: Peregrine Falcon," written by Edward Cascella, a Geoscientists-in-the-Parks intern, National Park Service; a work of the United States government in the public domain. Rewritten in hubnx's own words. The mercury figures are given in the units the article uses.
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