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Raptors: Movement Studies
Raptors: Movement Studies

Characterizing the Movement and Dispersal Patterns of Maine Subadult Bald Eagles Using Satellite Telemetry and Color Banding

BRI began small-scale efforts to band Maine Bald Eagle nestlings in 2001. By 2004, BRI and collaborators began intensive efforts to evaluate the exposure of Maine’s Bald Eagle population to mercury, which was prevalent in other wildlife across New England. To accomplish this, researchers climbed nest trees and lowered nestlings, typically about 6 weeks of age, to researchers waiting below. In addition to taking samples to be used for contaminant, genetics, and other analyses, researchers placed "silver" bands and red "color bands" on nestlings. The silver band, issued by the federal USGS Bird Banding Lab, contains a unique ID, a “social security number” of sorts – that band, if recovered, can be linked back to that individual’s original banding location and related information. On the leg opposite the silver band, researchers typically placed a colored band containing several large etched characters. Unlike silver bands, color bands can often be read from a distance with a spotting scope or digital camera, and this information can be used to identify the banding origin of that particular eagle.

Lead Investigators: Chris DeSorbo and Rick Gray

BRI’s Bald Eagle Banding Efforts

BRI’s Bald Eagle Banding Efforts

Over the past decade, BRI researchers fitted red color bands (currently Maine’s given color) to nearly 700 Bald Eagle nestlings throughout the state (Figure 1). This notable effort is a significant investment in our current and future understanding of Maine’s recovering Bald Eagle population. Amateur and expert photographers now encounter our Maine red-banded eagles throughout the Northeastern U.S. on a regular basis – BRI biologists commonly get 1-2 Bald Eagle band ‘encounters’ per week, and the frequency of these observations seems to be increasing! As of summer 2015, BRI has received information on more than 250 Bald Eagles banded as nestlings throughout the northeastern U.S. and Canada. Each one has a unique story, and often times – some great photographs to go along with it!

BRI’s growing database of band encounter information gives us an opportunity to better understand many aspects of the ecology and recovery of Bald Eagles throughout the New England region. For example, estimates of the age of first breeding are typically determined by observing known-aged individuals banded as nestlings. Observations of banded individuals can also help provide estimates of survival, natal dispersal (the distance from a bird’s natal area that it goes to breed itself), and movement patterns. All of these measures are important in understanding Bald Eagles’ continuing recovery from levels once considered dangerously low. We aim to use BRI’s extensive banding database to answer some of these important questions about Eagles that are important in making informed management and conservation decisions.

 
 Figure 1: Locations throughout Maine where Bald Eagle nestlings were banded by BRI and collaborators through numerous research efforts, 2001-2013.
Figure 1: Locations throughout Maine where Bald Eagle nestlings were banded by BRI and collaborators through numerous research efforts, 2001-2013.
Satellite Telemetry

Satellite Telemetry

Starting in 2005, BRI and its collaborators began tracking Bald Eagles using satellite telemetry. While initial efforts aimed to better understand the habitat use of Bald Eagles on Maine hydroelectric reservoirs, satellite-tagged eagles quickly revealed that they could teach us about a wide range of subjects. From 2005 – 2015, we have fitted 21 fledgling and 1 adult Bald Eagle with satellite units. These units, many of which are still active today, demonstrate the amazing potential to learn about wildlife using tracking technology. Compared to the passive approach of fitting a band to an individual and waiting for an ‘encounter’ – tracking using telemetry offers researchers the opportunity to document the daily movements of individuals for many consecutive years.

Our satellite-tagged individuals have especially demonstrated interesting and revealing information about Maine’s ‘subadult’ Bald Eagles. These eagles have traditionally been very difficult to study due to their tendency to roam the landscape widely – often for years – until they eventually establish a territory and consider breeding themselves. We’ve tracked Maine-reared Bald Eagle nestlings virtually to treeline in Quebec, Canada, and as far south as Virginia. Satellite-tracked eagles are helping us to determine what habitats are important to them for roosting and feeding during all months of the year, for both adult and subadult eagle age classes (i.e., 1-, 2-, 3-, and 4-year olds). For example, our moderate sample of satellite-tagged eagles is already helping to demonstrate the value of seasonally abundant food supplies, such as anadromous fish runs, to Bald Eagle populations. We are excited to track this cohort of eagles for years to come and tell their story to aid in conservation and management decision-making.

 
Figure 2: Locations throughout Maine where Bald Eagle Fledglings were instrumented with satellite transmitters, 2009-2015.
Figure 2: Locations throughout Maine where Bald Eagle Fledglings were instrumented with satellite transmitters, 2009-2015.
 
DeSorbo, C. R., D. Riordan, J. Tash, R. B. Gray and William Hanson. 2015. Documenting Areas of Importance to Maine Subadult Bald Eagles: Insights from Satellite Telemetry. Report #2014-24 submitted to the Maine Outdoor Heritage Fund, Portland, Maine, The Bailey Wildlife Foundation, Cambridge MA, and the Maine Department of Inland Fisheries & Wildlife, Bangor ME. 38 pp.
 

Project Collaborators

Biologists from the Maine Department of Inland Fisheries and Wildlife, the U.S. Fish and Wildlife Service, and NextEra Energy collaborated with BRI on efforts to band and sample nestling Bald Eagles.
 
Photo Credits: Header Photo: © BRI - Chris Persico; Banded eagle © BRI - Chris DeSorbo; Eagle with transmitter © Kristen Nicholas
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