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Raptor Program
Raptor Program

Studying Raptors as Sentinels of Ecosystem Health

Raptors are cherished sights to many who are fortunate enough to behold them. Whether it’s the sighting of a Bald Eagle skillfully plucking a fish out of the water, a Peregrine Falcon in a high-speed chase, or an owl quietly surveying the landscape from an inconspicuous perch, the charismatic nature of raptors often commands the attention of all who gaze upon them. Even beginner naturalists seem able to detect a raptor amidst other bird company.

The term “raptor” broadly refers to birds of prey. While not a taxonomic bird grouping, raptors are characterized by hooked bills and sharp talons. Ospreys, eagles, hawks, falcons, owls, vultures, and kites are all common raptors in North America, but the traits of species within these groups vary widely. For example, some raptors feed exclusively on birds, while others rely upon carrion or even snails.

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

Why Study Raptors?

Our answer at BRI is two-fold: to help species in need and to monitor our environment. As conservation biologists, we are representatives for the natural world. We study raptors to tell their stories as a means of aiding in their conservation. However, these birds have their own story to tell us about our environment.

Both their distribution and their living tissue (blood, feathers, eggs) can provide much information about the health of individual birds as well as the health of forests, rivers, and oceans that sustain all of us.

The absence or abundance of raptors in an ecosystem is meaningful. 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 focuses its research efforts on meeting the conservation needs of raptors, and using raptors as bioindicators to evaluate the health of individuals, populations, and ecosystems. Below, we have grouped our primary areas of research emphasis 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 systems polluted with contaminants, these compounds are often magnified up the food web to top predators. As a result, raptors are among the most well-established bioindicators, or “biosentinels.” Biosentinels such as the Bald Eagle, Osprey, and Peregrine Falcon are well-known. Their fates and histories are tightly intertwined with some of the most important environmental policies in U.S. history. For example, the 1973 Endangered Species Act provided for the conservation of ecosystems upon 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 about the short- and long-term exposure to contaminants through diet. Sampling broadly throughout the landscape helps biologists identify “hotspots” of contaminant exposure, and sampling annually helps us determine if contaminant levels are changing over time. Such information has proven pivotal in guiding policy decisions to regulate pollutants.

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

Movement Studies: Banding

Movement Studies: Banding

Efforts to study the movements of raptors help us learn critical information about their 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? The answers to such questions are more than just interesting; they are needed to make responsible conservation and management decisions that affect both wildlife and humans. 

How do we go about gathering information on raptor movements? Two approaches we emphasize are banding and tracking using telemetry.

Marking birds with unique leg bands is one of the most long-standing methods of studying birds. Traditional bands help us identify the banding origin of birds that are recovered or recaptured elsewhere.

Colored bands used on many raptors display unique etched characters which are readable in the field, enabling identification of birds from a distance. As a result, color bands are regularly noted by photographers and nature enthusiasts in addition to researchers. BRI’s raptor program continues to band hundreds of breeding and migrant raptors as part of our ongoing research and monitoring efforts.

Movement Studies: Tracking

Movement Studies: Tracking

With rapid advancements in tracking technology, we are able to gain detailed location information on birds that is helping us fill in major gaps in our understanding of their ecology. For example, we can 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 help inform decision makers about where to place wind power facilities, or provide land managers important information about habitat use.

Scientists use two primary types of transmitters to track individual bird movements: traditional (VHF) radio transmitters, and satellite transmitters. Birds fitted with traditional radio transmitters are typically tracked within a relatively close range (several miles) by plane, vehicle, or on foot using a receiver. Birds fitted with satellite transmitters can be tracked at a global scale because they relay location information via satellites. Developing tracking technology relays GPS locations using the cellular phone network.

To date, BRI researchers and our 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 research projects:

Surveys and Population Monitoring

Surveys and Population Monitoring

Conservation biologists are continually challenged to evaluate the status of bird populations. Importantly, we try to detect declines as they occur. We prioritize collecting information needed to detect and measure changes in the stability of raptor populations. In order to achieve this, we survey raptor populations to document the number of individuals, breeding pairs, nonbreeding pairs, nests, or 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 research projects:

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.
Biodiversity Research Institute