Everything You Always Wanted to Know about Eaglet Banding

Although the N.J. Endangered and Nongame Species Program and Conserve Wildlife Foundation had hoped to band the two Duke Farms eaglets next week, the plan has been scrapped  this year for reasons related to the difficulty of getting to the nest. While nothing can compare with witnessing an eaglet banding, here's a consolation prize: ENSP wildlife biologist Kathy Clark generously shared her expertise on the banding process in a recent interview for this blog.

Lets start with the question that Eagle Cam viewers keep asking:  How are the eagles banded with the parents nearby? Do the parents ever get aggressive toward the human retrieving the eaglets? The adults always stay nearby within view of the nest while we are there to band the young. They are rarely aggressive. As big birds, they are not very agile and don't feel safe attacking a person because it could be hard for them to fly off again. In our 30 years of banding eagles, no climber has ever been hit by an adult; it has happened, however rarely, to climbers elsewhere.

Why do you band them in early May -- it is a certain point in their development? We always aim for around 6 weeks of age.  The chicks are easiest to handle at that age.  Plus, if our timing is wrong by a week either side, the chicks are still bandable.

How do you get them down from the tree? We lower them down, one at a time, in a large cloth duffel bag.

What do the eaglets smell like? If the smell is noticeable, it's usually because of their fish prey.

How many folks are involved in the process, and what do they do? We usually have two biologists and a wildlife veterinarian with us, and we like to have a few more hands to carry equipment.

Besides banding the eaglets, what else transpires? We take a blood sample from each eaglet, then take a series of measurements that indicate age and sex. The blood samples are used to measure exposure to environmental contaminants, and more recently we're giving a tiny sample to a researcher who is studying the genetics of the eagle population in the US.

Can you tell the sex at this young age, and if so, how? The females are larger than males and that difference shows up at the 5-6 week age, and becomes clearer as they get older. The measurements we take are usually sufficient to sex them.

How long does the whole process take? About two hours, sometimes longer if the tree is bigger or more difficult to climb.

Biggest surprise while banding over the years? It's interesting to find an unhatched egg in a nest; we analyze unhatched eggs for contaminants, which is a different measure than nestlings. We have encountered a couple nestlings that were injured, one by a fishing lure that got stuck in his chest; our veterinarian was there to remove it and successfully treat the wound.

How many eaglets will you band this year? We have banded about 20/year in recent years, but I think it will be fewer nests visited this year.

Will you be putting transmitters on any eaglets this year? We may attach a transmitter to an eaglet in south Jersey.

How many eaglets have you banded over the years? 399 between 1993 and 2014.

Why band the eaglets?  What have you learned? We've learned that eagles of NJ origin nest mostly in NJ but also in NY, CT, MA, PA, DE and MD. The oldest eagle of NJ origin was about 25 years old and had nested on Aberdeen Proving Ground her whole life.

Hooded eaglet with transmitter.

We also know that about 50% of young eagles don't make it, but that once they reach adulthood their survival rate is over 90%. Satellite transmitters are telling us a whole lot more. The movement of young eagles, before they're tied to a nesting area, is wide-ranging, but also shows they will use good habitats repeatedly through the year for roosting and foraging.

Whats the farthest away from New Jersey that you have gotten a sighting of an eagle banded in NJ? Just last year, a young bird was resighted (and then died, unfortunately) in Maine. But our transmittered eaglet from 2014 spent the fall and early winter in a remote area of Quebec, which we would not have known without the transmitter. Those long movements by eagles in their first year may be quite common but have gone mostly undetected.

Got a question or suggestion? E-mail Jim at wrightjamesb@gmail.com 

Jim Wright writes The Bird Watcher columnist for The Record and the Herald-News. He is the author of four coffee-table books about wild places, and the deputy marsh warden of the Celery Farm Natural Area in Allendale, N.J.