In July 2014, two Bald Eaglets were fitted with GPS transmitters prior to their August release at Chincoteague Island. Regular Wildlife Center website visitors might be familiar with Bald Eagle NX’s travels – we have enjoyed watching NX explore Virginia for nearly three years. The transmitters for these two 2014 eaglets are the same make and model as NX’s, though have some slight differences. Here are answers to some frequently asked questions.
Q: Why were the eaglets fitted with transmitters?
A: These two eaglets will be a part of a larger, ongoing research study that will monitor eagle movements. This study looks at the data received from these Bald Eagles to determine the range and behavior of Bald Eagles in Virginia’s coastal plain. Migratory behavior is studied as biologists are able to see how far Bald Eagles move in the winter season, and the data will play an important role in modeling how these birds use airspace. By looking at heights at which the eagles fly, average distances, and other specifics, biologists are able to relate this eagle behavior to real-life issues, such as airstrike data. During the past few years, VDGIF Biologist Jeff Cooper has fitted many Bald Eagles with GPS transmitters.
For the Wildlife Center, this is a fantastic opportunity for additional post-release studies of our rehabilitated raptors. There have been very few studies done in this area. We look forward to watching the movements and behaviors of young birds that have been at our facility.
Q: How does the transmitter work?
A: These types of transmitters use satellites to record GPS information. By using a cellular network to transmit data, the transmitters are able to provide GPS points every 15 minutes. During one seven-day period each month, the satellites will record GPS information every 30 seconds, so that researchers 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.
These transmitters are designed to send data every day.
Q: How are the transmitters attached to the birds?
A: GPS transmitters are fitted on eagles with Teflon straps – similar to how a human would wear a backpack.
Q: Won’t the transmitter weigh the eagle down?
A: No, the transmitter is very light and weighs 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 birds, the transmitters are less than two percent of the birds’ body weights.
Q: How long will the transmitter last?
A: These types of transmitters have lithium batteries but also are adapted with solar chargers. The biologists estimate these particular transmitters will last between one to two years. They are still learning about the battery life in these transmitters due to the different data parameters; the life of the battery should be shorter than the battery life of NX’s transmitter, since her “data dump” was set to every other day, and her data points were recorded every 15 minutes. These are rough estimates; the prediction was for NX’s battery to last about two years, and as of July 2014 it has been three years and she’s still checking in!
Q: Will the transmitter fall off after the battery expires?
A: These transmitters are permanent and 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 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 are used when researchers want to recover the transmitters.
Q: How often will we be able to see where the eagle is?
A: Once the birds are released, the tracking device should record a data update every day. A standard time will be set on the transmitter so that data comes in at the same time each day. However, transmitting the data also requires that the bird be “in-range” at the check-in time.
For example, if the transmitter is set for a data download at 3:00 pm EST – we will receive that information at 3:00 p.m. every day. However, if the bird flies out of cell phone range on a transmitting day from 2:55 p.m. to 3:05 p.m. – the data will not be received that day. It will be stored, however, so that if the eagle is back in range the next day, all movements will be tracked and recorded.
Please bear in mind that the WCV staff will be checking in to the tracking system to receive the data – and we will have to upload the data and maps to our website. Because there is a human working on providing this information, we will not be able to upload maps every day to the website. We should be able to provide updates once or twice a week.
Q: Will the eaglets fly long distances?
A: We’ll have to wait and see! 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 only spend about two to five percent of each day [24-hour period] in flight. More than half of their time is spent roosting, and about a third of their time is spent perching.
Some eagles choose to stay in Virginia year-round; NX, for example, has remained in or very near Virginia since her August 2011 release. Many other Bald Eagles travel around the Eastern Seaboard. We’ll have to tune in to see the adventures of these eaglets.