The Recovery of the American Peregrine Falcon in Alaska

Abstract

American Peregrine Falcons nesting along Alaska’s upper Yukon River have been studied for nearly 50 years. Peregrine populations decreased in the 1960’s because widespread use of the insecticide DDT caused their eggshells to thin. Thin eggshells meant that eggs crushed easily in the nest, which reduced the number of baby birds produced. Eventually, Peregrine Falcons were listed as endangered under the Endangered Species Act in the United States (U.S.). After the U.S. banned the use of DDT, the U.S. Fish and Wildlife Service, National Park Service, and others helped Peregrine Falcons recover. Today, upper Yukon River Peregrine Falcons have rebounded and are thriving. The Peregrine Falcon’s recovery in the U.S. is a shining success story of the Endangered Species Act, although climate change and other pollutants create continuing challenges for the species.

Full text

BIODIVERSITY
Published: 11 April 2022
doi: 10.3389/frym.2022.714834
THE RECOVERY OF THE AMERICAN PEREGRINE
FALCON IN ALASKA
David C. Payer 1* and Melanie J. Flamme 2*
1National Park Service, Anchorage, AK, United States
2Yukon-Charley Rivers National Preserve, Fairbanks, AK, United States
YOUNG REVIEWERS:
RANJAI
AGE: 12
RANVIR
AGE: 11
SHAHAR
AGE: 12
American Peregrine Falcons nesting along Alaska’s upper Yukon
River have been studied for nearly 50 years. Peregrine populations
decreased in the 1960’s because widespread use of the insecticide
DDT caused their eggshells to thin. Thin eggshells meant that
eggs crushed easily in the nest, which reduced the number of
baby birds produced. Eventually, Peregrine Falcons were listed as
endangered under the Endangered Species Act in the United States
(U.S.). After the U.S. banned the use of DDT, the U.S. Fish and Wildlife
Service, National Park Service, and others helped Peregrine Falcons
recover. Today, upper Yukon River Peregrine Falcons have rebounded
and are thriving. The Peregrine Falcon’s recovery in the U.S. is
a shining success story of the Endangered Species Act, although
climate change and other pollutants create continuing challenges for
the species.
kids.frontiersin.org April 2022 | Volume 10 |Article 714834 |1

Payer and Flamme Peregrine Falcons in Alaska
Figure 1
Figure 1
(A) An
American Peregrine Falcon
pair in Yukon-Charley
Rivers
National Preserve,
Alaska (photo credit:
Sean Tevebaugh, NPS).
(B) A perched female
American Peregrine
Falcon. Note the bright
yellow talons (photo
credit: Melanie
Flamme, NPS). THE AMERICAN PEREGRINE FALCON
The upper Yukon River in Alaska is home to one of the world’s most
well-studied populations of American Peregrine Falcons. Peregrine
Falcons are large, stocky falcons with dark, slate-colored feathers on
their backs, lighter feathers on their stomachs, and distinctive facial
markings (Figure 1A). They have bright yellow, clawed feet called
talons, used for perching and catching prey (Figure 1B). We monitor
these birds along a 265-km (165-mi) section of the Yukon River in
Yukon-Charley Rivers National Preserve (Figure 2A), in Alaska, U.S. A
preserve is like a national park created to protect wildlife, habitat, and
history. The high, steep, golden blus found here are an important
BLUFF
A cli rising steeply
from the banks of a
river, typically having a
broad flat or
rounded front.
Peregrine Falcon nesting habitat. They provide a safe place to raise
young and good viewing to look for prey. Each summer, Peregrine
Falcons return to the upper Yukon River from their winter ranges, as
far away as Argentina, to mate and raise chicks.
Falcons are birds of prey, meaning they hunt other animals for food.
Peregrine Falcons are among the fastest birds in the world. Diving
from above, they can reach over 322 km/h (200 mi/hr). This helps
them catch their favorite meal—other birds. Using their sharp vision,
they target prey in mid-air, chase it, and strike with a sharp blow
of their talons. Though they are powerful predators, the species
SPECIES
A group of similar
organisms that can
breed together.
has faced dicult challenges. As a top predator in the ecosystem,
human activities such as pollution and climate change can threaten
Peregrine Falcons.
DAMAGE FROM AN INSECTICIDE AND HELP FROM A
LAW
Dichloro-diphenyl-trichloroethane, or DDT for short, is an insecticide
DICHLORO-DIPHENYL
-TRICHLOROETHANE
(DDT)
A toxic chemical used
to kill insects and crop
pests. It caused
eggshell thinning in
many birds.
introduced in the U.S. in 1947. It was used to kill insects that were
pests on crops and that caused human diseases. But DDT had
other, unintended eects on the environment. When birds ate insects
contaminated with DDT, they themselves became contaminated. As
Peregrine Falcons fed on contaminated birds, the contamination was
passed on to them in ever-increasing amounts. In Peregrine Falcons
and other birds, one eect of DDT was to interfere with egg formation,
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Payer and Flamme Peregrine Falcons in Alaska
Figure 2
Figure 2
(A) The upper Yukon
River flows 266 km (165
miles) between the
Canadian border and
Circle, Alaska.
Yukon-Charley Rivers
National Preserve,
Alaska, is outlined in
green and the straight
green line at the right
of the map shows the
boundary with Canada.
Inset shows the
location of the preserve
in Alaska with national
park lands in green. (B)
Biologists travel by
motorboat and use
binoculars and spotting
scopes from riverbanks
to look for Peregrine
Falcons on blus
(photo credit: Josh
Spice, NPS).
resulting in eggs with thin shells. The fragile shells made the eggs
susceptible to being crushed in the nest. As a result, nesting birds
produced fewer chicks. By the 1960’s, many species of birds, including
Peregrine Falcons, declined across North America because of DDT.
Peregrine Falcons disappeared completely from the eastern U.S. at
this time.
The U.S. banned the use of DDT in 1972. In 1973, Peregrine Falcons
were listed as endangered under the Endangered Species Act (ESA).
ENDANGERED
SPECIES ACT (ESA)
A U.S. law enacted in
1972, designed to
protect and conserve
threatened and
endangered species
and their habitats.
The ESA is the primary U.S. law that protects imperiled species and
their habitats. Eorts started soon after to help the species recover,
led by the U.S. Fish and Wildlife Service. In Alaska, scientists tracked
the number of breeding Peregrine Falcons nesting along the upper
Yukon River. They measured the amount and types of toxins in the
Peregrine Falcons’ feathers and eggs. More needed to be done to
protect Peregrine Falcons, however, because they migrate through
other countries and needed protection there, too. Joint eorts by
many countries and groups helped the species recover. Although DDT
is still used in some areas outside of the U.S., its use worldwide has
been much reduced. Further, breeding programs helped baby birds
survive and Peregrine Falcons were reintroduced into areas where
they had disappeared. The recovery of Peregrine Falcons in Alaska
occurred naturally, without breeding programs or reintroductions, but
such programs were essential to the overall recovery of the species
in many areas outside of Alaska where the species had suered
severe declines.
OTHER THREATS TO PEREGRINE FALCONS
Impacts from DDT have been reduced and, while that is good news,
other forms of pollution can still harm Peregrine Falcons and other
birds. Alaska is remote and the environment there is in pretty good
shape. But global pollution carried by air currents still finds the
falcons. One pollutant, mercury, can be especially toxic to wildlife.
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Payer and Flamme Peregrine Falcons in Alaska
Mercury is an element that occurs in nature. It is released into the
air during mining, manufacturing, and the burning of waste. Once
released, mercury can be chemically changed into methylmercury
by tiny microorganisms in lakes and ponds. When this happens,
methylmercury gets into small organisms like insects living in the
water. Those insects are then eaten by larger living things, such as fish
and birds. Methylmercury is toxic to birds, aecting multiple organs
and egg development. Because Peregrine Falcons are at the top of
the food web, they are more likely to consume toxins from their prey.
Over the birds’ lifetimes, these toxins can build up inside their bodies.
Unfortunately, the levels of mercury found in Peregrine Falcon eggs
along the Yukon River are cause for concern and, if the mercury levels
continue to rise, it could cause failure of eggs to hatch.
Climate change is another threat to Peregrine Falcons. Weather
patterns and winds are changing, storms are getting stronger and more
frequent, and summer air temperatures are warmer, which can stress
the birds. Also, some of the Peregrine Falcon’s favorite prey species are
shifting their distributions or becoming less abundant, making them
less available as a meal. All these things can threaten the health of
Peregrine Falcons.
HELPING PEREGRINE FALCONS THROUGH LONG-TERM
MONITORING
One of the reasons the Yukon-Charley Rivers National Preserve was
created was to protect Peregrine Falcons and their nesting habitat. We
monitor Peregrine Falcons because they are at the top of the food web
and can be indicators of ecosystem health. We track animals and their
environments to assess ecosystem health over time.
In the preserve, we monitor Peregrine Falcons twice each year to
determine their health and numbers [1]. In May, we make our first trip
down the Yukon River to count the number of Peregrine Falcons and
record which blus are being used for nesting. In July, we return to
count the number of fuzzy, white chicks in each nest, which is typically
between 0 and 4.
Traveling by motorboat, we search the blus along 266 km (165 mi) of
the upper Yukon River, from Circle, Alaska to the border with Yukon,
Canada and back downriver again (Figure 2A). We count the total
number of Peregrine Falcons, both mating pairs and single birds, seen
at over 175 blus. These high, steep blus provide Peregrine Falcons
with protection from predators, especially for their nestlings. We find
birds by using binoculars and spotting scopes, and we watch from the
riverbanks or islands (Figure 2B). We have photographs of all nesting
blus and mark them with all nests found. Nest sites are called eyries.
EYRIE
A nesting site of a bird
of prey, often found
high on blus or
in trees.
Our photographs help us to quickly find eyries and check for birds
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Payer and Flamme Peregrine Falcons in Alaska
Figure 3
Figure 3
Two American
Peregrine Falcon
nestlings in an eyrie
along the upper Yukon
River in Yukon-Charley
Rivers National
Preserve, Alaska (photo
credit: Melanie
Flamme, NPS).
in subsequent years because Peregrine Falcons tend to re-use the
best sites.
Peregrine Falcons make nests in the eyries by scraping the ground with
their bellies. They lay up to four rusty-brown eggs. The nestlings are
fragile for their first 2 weeks of life (Figure 3). They can easily overheat
or get too cold. Both parents work hard to continuously protect
their chicks. They take turns hunting, feeding, shading, warming, and
protecting them. After 30 days, the young falcons have grown from
fluy white cotton balls to hulking, black-and-white teenagers. By fall,
they have learned to fly and they leave the nest to migrate south.
Nearly 50 years of monitoring shows that the number of Peregrine
Falcons in the preserve has increased and is now leveling o. Our
study tracked the natural recovery of an endangered species from
a population crash to healthier levels. We looked at the Peregrine
Falcon recovery from 1977 to 2015, to see how many falcons were
occupying each blu and how many nestlings were produced. We
observed 1,602 occupied territories and 2,349 nestlings over those
years. The fastest increase in Peregrine Falcon numbers was in the
1970’s and 1980’s. The increase slowed in the 1990’s and 2000’s. As
the number of occupied blus grew, the distance between them got
smaller and Peregrine Falcon territories got closer together. Blus
got more crowded as birds competed for good nest sites. With
closer neighbors, the numbers of nestlings dropped. This is probably
because pairs were competing for food to feed their young and were
spending more time defending their territories from other birds. In
recent years, the Peregrine Falcon population has remained fairly
steady, which suggests the habitat along the river may now be fully
occupied [2].
It took nearly 50 years for Peregrine Falcons to recover from the
damage caused by DDT. The Peregrine Falcon population along the
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Payer and Flamme Peregrine Falcons in Alaska
upper Yukon River has grown from 12 breeding pairs in 1975 to over
60 pairs today. This is a shining example of the power of international
teamwork, long-term monitoring, and eective environmental laws.
We will continue to monitor and protect the Peregrine Falcons in the
preserve as they face new threats from pollutants and climate change.
We hope these continued eorts will help Peregrine Falcons endure
future challenges1.
1For more on these
falcons, see the
video: The American
Peregrine Falcon of
Yukon-Charley
Rivers National
Preserve:
https://www.nps.gov
/media/video/view.
htm?id=58132444
-1DD8-B71B-0BC146
92FB439ECD
FUNDING
The funding for this work was provided by the U.S. Fish & Wildlife
Service and the National Park Service.
ORIGINAL SOURCE ARTICLE
Ambrose, S., Florian, C., Ritchie, R. J., Payer, D., and O’Brien, R. M. 2016,
Recovery of American peregrine falcons along the upper Yukon River,
Alaska. J. Wildlife Manag. 80:609–20. doi: 10.1002/jwmg.1058
REFERENCES
1. Ambrose, S., Guldager, N., Daw, S., Beer, M., Flamme, M. J., MacCluskie, M., et al.
2018. American Peregrine Falcon Monitoring Protocol for the Central Alaska
Network: Protocol Narrative, Version 2.0. Natural Resource Report
NPS/CAKN/NRR−2018/1747. Fort Collins, CO: National Park Service. Available
online at: https://irma.nps.gov/DataStore/DownloadFile/608645
(accessed March 23, 2022).
2. Ambrose, S., Florian, C., Ritchie, R. J., Payer, D., and O’Brien, R. M. 2016,
Recovery of American peregrine falcons along the upper Yukon River, Alaska. J.
Wildlife Manag. 80:609–20. doi: 10.1002/jwmg.1058
SUBMITTED: 25 May 2021; ACCEPTED: 10 March 2022;
PUBLISHED ONLINE: 11 April 2022.
EDITOR: Rebecca Weissinger, National Park Service, United States
SCIENCE MENTORS: Varsha Singh and Asaf Gal
CITATION: Payer DC and Flamme MJ (2022) The Recovery of the American
Peregrine Falcon in Alaska. Front. Young Minds 10:714834. doi: 10.3389/frym.2022.
714834
CONFLICT OF INTEREST: The authors declare that the research was conducted in
the absence of any commercial or financial relationships that could be construed
as a potential conflict of interest.
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Payer and Flamme Peregrine Falcons in Alaska
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AUTHORS
DAVID C. PAYER
Dr. David Payer is the regional wildlife biologist for the National Park Service in Alaska.
His research interests include determining the eects of human activities, pollution,
and climate change on wildlife in parks, and developing ways to minimize adverse
eects. He often consults with parks throughout the U.S. on wildlife-management
practices that will preserve healthy animal populations and provide opportunities for
people to enjoy observing wildlife in its native habitats. *david_payer@nps.gov
MELANIE J. FLAMME
Melanie Flamme is a wildlife biologist for the National Park Service at Yukon-Charley
Rivers National Preserve. Her research interests include studying songbirds, loons,
Peregrine Falcons, and small mammals, like voles and mice. She also helps youth
learn about science in the parks to develop the next generation of park scientists.
*melanie_flamme@nps.gov
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