Post-Release Monitoring of Rehabilitated Raptors

During my three-month rehabilitation externship with the Wildlife Center of Virginia I have seen the rescue, rehabilitation, and release of many animals, including three Eastern Screech-owls, two Great Horned Owls, one Cooper’s Hawk, one Ruddy Duck, one Canada Goose, three Big Brown Bats, one Virginia Opossum, and one Mink ... and so many more releases are planned for the near future! All of this left me wondering what happens to these animals after they are released back into the wild? Do they make it out there on their own? Where do they go? What do they do?

Post-release monitoring of rehabilitated animals is not a widely explored field. But why not? Isn’t it really important to know what happens to the animals so that we know rehabilitation effort is paying off, and adjust our methods based on what we learn? Yes! However, as costly and time-consuming as rehabilitation is, post-release monitoring is even more so and thus not often practiced. Monitoring of threatened and endangered species by scientists using various telemetry, GPS, tagging, and other techniques is a much more common practice, which is often funded through research grants. If there’s one thing the Wildlife Center of Virginia is really big on, it is teamwork, with externs running around like chickens with their heads cut off all day and a fantastic network of volunteers across the state always willing to lend a helping hand. So, it did not come as a surprise to me when I found out that WCV is collaborating with the Virginia Department of Game and Inland Fisheries, and using GPS tracking to monitor post-release movements of Bald Eagles.

This study, led by VDGIF biologist Jeffrey Cooper, has been looking at the geographic range of bald eagles in Virginia’s coastal plain, and also observes their migration and nesting behavior and general habitat use. “We need to know what areas are of highest importance to ensure that high-quality habitat is not lost,” says Jeffrey Cooper. Jeff Cooper has been fitting wild-caught Bald Eagles with GPS transmitters for the past few years, and, recently, the Wildlife Center has been “supplying” rehabilitated eagles to the study as well. The GPS transmitters weigh 100 grams and are fitted onto the eagles back with an X-strap that goes under the feathers of the wings and across the chest. The transmitters record GPS location, altitude, and traveling speed every 15 minutes using satellite networks, and send this data (plus transmitter battery life) back to a central database over cellular networks once a day (can be longer if the animal is in an area with poor reception, or if its battery is low). The transmitters run on a lithium battery that is charged using a small solar panel on the device, and are expected to last for approximately two to three years on each eagle.

More than a dozen eagles released from WCV have been fitted with these devices since 2011. Many transmitters are still actively sending data; a few have stopped transmit but given that these birds were on the move when we lost contact it is assumed that they are still alive. One eagle has been confirmed to have died, with its carcass and transmitter recovered shortly after release, and one other is suspected to have died, as it was transmitting from the same spot before the transmitter gave out, though its body and transmitter have not been recovered. Most rehabilitated eagles are presumably alive and well. This tells us that our eagles seem to be able to survive on their own in the wild after spending time recovering at WCV. However, unless we compare the mortality we saw to an estimate of wild hatch-year and adult eagle mortality we cannot draw a conclusion about the success of rehabilitation in releasing fully functioning eagles. The USFWS suggests survival of hatch-year birds is less than 50%, whereas for adults is greater than 90%. So, in comparison to this estimate of wild bird survival, WCV eagles have done quite well.

Is there any other post-release monitoring on WCV birds? Not directly, however all released raptors are tagged prior to release. Raptors receive small metal bands around their leg and band numbers are entered into the Patuxent Wildlife Research Center Bird Banding Laboratory database through the USGS. If a bird is ever recovered, then WCV is informed but it is rare to hear back about any of the birds.

This post-release research is encouraging in showing that rehabilitation efforts generally seem successful in restoring functional wild animals, and are useful to study the effects of different rehabilitation techniques to suggest best practices. While it’d be nearly impossible to set up detailed, long-term monitoring on all animals released from rehabilitation programs, the few programs and studies that have been/are being done show great promise for post-release survival, and thus rehabilitation success. Speaking of which, you can follow WCV’s eagles right here on our website (look under the Critter Corner tab), and see what they’ve been up to since their release, and keep tabs on where they’re heading next!

WCV Class of 2016

Booth, G.C. Up close with the Nations Symbol. Virginia Wildlife (July 2009): 18-21. 
Fajardo, I., Babiloni, G., nd Miranda, Y. 2000. Rehabilitated and wild barn owls (Tyto alba): dispersal, life expectancy and mortality in Spain. Biological Conservation 94: 287-295.
Golightly, Richard T. et al. 2002. Survival and Behavior of Western Gulls Following Exposure to Oil and Rehabilitation. Wildlife Society Bulletin 30.2: 539–546.
Lander, M.E. et al. 2002. Behavior, Movements, and Apparent Survival of Rehabilitated and Free-Ranging Harbor Seal Pups. The Journal of Wildlife Management 66: 19-28.