Biodiversity Research Institute
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Raptor Program
Raptor Program

Studying Raptors as Sentinels of Ecosystem Health

Raptors command attention, whether a Bald Eagle skillfully plucking a fish from water, a Peregrine Falcon in high-speed chase, or a Barred Owl surveying the landscape from an inconspicuous perch. While the term “raptor” is not a taxonomic bird grouping, it refers to birds of prey characterized by hooked bills and sharp talons. However, other traits within this group vary widely: while some raptors feed exclusively on birds, others rely upon carrion, and some even on snails. In North America, common raptors include eagles, falcons, owls, hawks, ospreys, vultures, and kites.

Program Director: Chris DeSorbo
Program Staff: Chris Persico, Lauren Gilpatrick

Why Study Raptors?

Raptors serve as bioindicators for the health of their ecosystems. Their distribution, population level, and living tissues (blood, feathers, and eggs) provide information not only about raptor health, but the health of forests, rivers, and oceans. Because of these relationships, the near extirpation and recovery of several raptor species is tied to important U.S. environmental policies, such as the banning of DDT and the Endangered Species Act. BRI studies raptors to better aid in their conservation, and the conservation of crucial ecosystems.

BRI's raptor research team focuses its efforts on the conservation needs of raptors, while also using raptors as bioindicators of individual, population, and ecosystem health. Our primary research is grouped into three nonexclusive areas: (1) contaminants monitoring; (2) movement studies; and (3) surveys and population monitoring.

Contaminants Monitoring

Contaminants Monitoring

Many raptors sit at the top of the food web, often feeding on fish and other birds. In polluted systems, contaminants are often magnified to top predators through the food web. As a result, raptors are well-established bioindicators, or “biosentinels.” The history of well-known biosentinels, such as the Bald Eagle, Osprey, and Peregrine Falcon is intertwined with some of the most important environmental policies in the U.S. For example, the 1973 Endangered Species Act provided for conservation of ecosystems on which threatened and endangered species of fish, wildlife, and plants depend.

For decades, biologists have sampled birds to evaluate the potential for reproductive or behavioral impacts due to contaminant exposure. Bird blood, feathers, and eggs provide direct insights into the short- and long-term exposures to contaminants through diet. Sampling broadly throughout the landscape helps biologists identify “hotspots” of contaminant exposure, and sampling annually helps determine if contaminant levels change over time. This information has proven pivotal in policy decisions to regulate pollutants.

Below is a selection of representative raptor contaminants monitoring research projects:

Movement Studies

Movement Studies

Movement studies help us learn critical information about raptor behavior and ecology. How long does a raptor remain in its natal area before it disperses, and where might it eventually go to breed? Do raptor movement patterns place these birds at a high collision risk with wind turbines or other structures? Answers are needed in order to make responsible conservation and management decisions that affect wildlife and humans.

We gather information of raptor movements through banding and tracking studies. Banding birds with unique leg bands is one of the most long-standing methods for studying birds. Bands help identify the banding origins of birds recovered or recaptured elsewhere. Colored bands used on raptors display unique etched characters that enable researchers to identify birds from a distance. As a result, color bands are regularly noted by photographers and nature enthusiasts as well. BRI’s raptor program bands hundreds of breeding and migrant raptors as part of our ongoing research and monitoring efforts.

Researchers use traditional (VHF) radio transmitters and satellite transmitters to track individual bird movements. Birds fitted with traditional radio transmitters are tracked within a relatively close range (several miles) by plane, vehicle, or foot using a receiver, while birds with satellite transmitters can be tracked at the global scale.

Rapid advancements in tracking technology allow us to gain detailed location information on birds that helps fill in major gaps in the understanding of their ecology. We can now answer questions such as: How far offshore do migrant Peregrine Falcons fly? How important are anadromous fish runs to Maine’s recently fledged Bald Eagle population? Detailed data on raptor movements can inform decision makers on where to place wind power facilities, or can provide land managers with important habitat use information.

To date, BRI researchers and collaborators have tracked a variety of raptors including Bald Eagles, Peregrine Falcons, Ospreys, and Great Horned Owls. These individuals continue to provide remarkable information that is valuable in a wide spectrum of research, management, conservation, and legislative decisions.

Below is a selection of representative raptor movement studies:

Surveys and Population Monitoring

Surveys and Population Monitoring

Conservation biologists are continually challenged with evaluating changes in bird populations as they occur. We prioritize collecting information needed to detect and measure changes in the stability of raptor populations. We survey raptor populations to document the number of individuals, breeding pairs, nonbreeding pairs, nests, and young produced in an area. Birds can be detected by direct observation (counting), sound (responses to playback calls), or by capturing and banding them.

Below is a selection of representative raptor survey and monitoring studies:

Program Director
Christopher R. DeSorbo
207-839-7600 x115

Program and Contributing Staff
Lauren Gilpatrick
Bill Hanson
Chris Persico


Photo Credits: Header photo: © Daniel Poleschook. Study Subjects: Bald Eagle © Sharon Fiedler; Peregrine Falcon © Ken Wright; American Kestrel © iStock; Merlin © Ken Wright; Northern Saw-whet Owl © BRI-Chris DeSorbo. Eagle nest © BRI-Chris DeSorbo. Banding BRI-Chris DeSorbo. Peregrine with sat tag BRI-Jonathan Fiely. Sea plane © Ken Wright. Merlin in can © Ken Wright.
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