From 2011-2022, the Wildlife Center tracked the post-release movements of nearly two dozen former eagle patients. In most cases, these GPS transmitters were provided by the state eagle biologist, and the data on the birds were part of a larger, ongoing research study that monitors eagle movements to determine the range and behavior of eagles in Virginia’s coastal plain. For the Center, this was an invaluable opportunity to track the movements of some of our rehabilitated patients.
Center staff and followers tracked many of these eagles for months. In some cases, the transmitters appeared to have failed after some time; in three cases, the eagles died several months post-release. Three eagles — NX, W20, and MN72 — were tracked for five years or more!
Tracked Bald Eagle Patients
WCV Patient Number | Post-release | Released | Release Location | Months Tracked |
|---|---|---|---|---|
February 2011 | Harvey's Knob Overlook | 1 | ||
NX | August 2011 | Berkeley Plantation | 5 years! | |
C35 | August 2014 | Chincoteague | 17 | |
C46 | August 2014 | Chincoteague | 5 1/2 years! | |
NC99 | December 2014 | Natural Chimneys | 8 | |
W20 | August 2015 | Widewater State Park | 5 1/2 years! Confirmed death from lead poisoning. | |
YR73 | September 2015 | York River State Park | 1; suspected death | |
GW91 | September 2015 | George Washington Birthplace | 2; confirmed death | |
SML52 | October 2015 | Smith Mountain Lake | 7 | |
BI78 | October 2015 | Belle Isle State Park | 13 | |
KG09 | November 2015 | King George County | 5 years; suspected death | |
BP39 | December 2015 | Berkeley Plantation | 12 | |
BP91 | December 2015 | Berkeley Plantation | 10; confirmed death (likely electrocuted) | |
BI20 | August 2016 | Belle Isle State Park | 2 | |
Saltville GOEA | November 2016 | Big Walker Lookout | 4 | |
BP28 | September 2016 | Berkeley Plantation | 5 | |
CP93 | November 2016 | Chippokes Plantation State Park | 12; confirmed death (hit by vehicle) | |
MN18 | August 2017 | Mason Neck State Park | 29; died, body unrecovered | |
MN72 | August 2017 | Mason Neck State Park | More than 5 years | |
RR53 | July 2018 | Rappahannock River Valley National Wildlife Refuge | Nearly 3 years; died, body recovered |
Frequently Asked Questions about Eagle Transmitters
Why do you put transmitters on some eagles before release?
The eagles that wear GPS transmitters are part of a larger, ongoing research study that monitors eagle movements. This study looks at the data received from Bald Eagles to determine the range and behavior of the eagles in Virginia’s coastal plain. Migratory behavior is studied as biologists can see how far Bald Eagles move in the winter season, and the data plays an important role in modeling how these birds use airspace. By looking at the heights at which the eagles fly, average distances, and other specifics, biologists can relate this eagle behavior to real-life issues, such as airstrike data. For the past decade or more, VA Department of Wildlife Resources Biologist Jeff Cooper has fitted hundreds of Bald and Golden Eagles with GPS transmitters.
For the Wildlife Center, having access to the data on tracked eagles is a fantastic opportunity for additional post-release studies of our rehabilitated raptors. There have been very few studies done in this area. Watching the movements and behaviors of birds that have been treated and released provides valuable insight into wildlife rehabilitation.
How does the transmitter work?
These types of transmitters use satellites to record GPS information. By using a cellular network to transmit data, the transmitters can provide GPS points as often as every 15 minutes, though researchers may also set parameters to record GPS information every 30 seconds, so they can create and utilize three-dimensional maps for their research. Data is temporarily unavailable when the birds fitted with these units fly out of cell phone range, but all information is stored and readily available once the bird is back in range.
How are the transmitters attached to the birds?
GPS transmitters are fitted on eagles with Teflon straps – similar to how a human would wear a backpack.
Won’t the transmitter weigh the eagles down?
No, the transmitters are very light and weigh less than 80 grams. In general, when transmitters are fitted onto eagles and other large birds, it is recommended that the weight of the backpack not exceed three percent of the bird’s body weight. For these eagles, the transmitters are less than two percent of body weights. In 2018, a new generation of transmitters were put into use; these were even lighter.
How long will the transmitter last?
This type of transmitter relies on lithium batteries but the units are also adapted with solar chargers. The biologists estimate these particular transmitters last between one to two years, though it's very dependent on how often data points are set to record and how often the "data dumps" come through. Some transmitters have lasted five years or more!
Will the transmitter fall off after the battery expires?
These transmitters are permanent; they will either stay on for the lifespan of each bird or will be taken off if the battery is dead and the birds are ever caught.
When the GPS transmitter is placed on a bird, the vital part of the fitting that secures the backpack in place is the piece of line that holds the two straps together. While cotton string [which can degrade] can be used, the biologists working on this study prefer working with an alternative material. West Virginia University Professor and Cellular Tracking Technology biologist Dr. Todd Katzner prefers using a stronger woven line that won’t break down. Dr. Katzner, who has been attaching transmitters to birds for more than 15 years, feels that this option is safer for the birds in the long run because it is unlikely to partially fall off, leaving a dangling strap that could entangle the bird.
Generally speaking, the tear-away variety is used when researchers want to recover the transmitters.
How far will the eagles fly?
Check out the individual tracking stories and find out! In general, a Bald Eagle’s daily activity depends on the age of the bird and the season. According to the Birds of North America online, some studies suggest that immature eagles spend less than two percent of their time flying and eating; more than half of their time is spent roosting, and about a third of their time is spent perching. Adults typically spend a little more time in flight, but still spend the majority of their time perching and roosting.
Some eagles choose to stay in Virginia year-round; Bald Eagle NX, for example, remained in or very near Virginia in her five-year tracking period. We've seen other eagles travel much farther -- Bald Eagle NC99 flew from Virginia to South Carolina for several months before he returned to central Virginia. After months of hanging out along the Potomac River, MN18 flew to Canada! Many other Bald Eagles travel around the Eastern Seaboard.