June 7 Notes - banding eagles
From our eagle surveys, we now know the web cam eaglets are among the oldest in the state. Their baby down is rapidly being replaced by dark brown contour, wing, and tail feathers. The feathers grow from blood quills, which you can see at the base of the large wing feathers in the last picture posted above (they look like a blue drinking straw). Young eagles are chocolate brown in color. They do not get a pure white head and tail until about five years of age. Their beaks and iris are dark brown and will not start to turn yellow for another 2 or 3 years. Both eaglets are growing rapidly and likely weight about 6 to 8 pounds - about 1/2 to 2/3 the weight of their parents. At this time the chicks are starting to exercise their wings, but they have to be careful or they will damage the blood quills. The wing beating exercises will increase in frequency in another week or two when their wing and tail feathers are fully developed and harden. As observers have noted, the adults are rarely within view of the web cam, but they are nearby hunting and guarding the nest. You've also noticed that we have been getting a lot of rain in Maine in the last two weeks. These chicks are likely old enough to tough it out without Mom's help, but I've seen them often huddled together to keep warm. Younger chicks don't fare as well. We've already documented several advance-aged chicks that died in other nests during our aerial surveys.
Since the early days of eagle recovery, biologists in Maine and elsewhere have used banding as a technique to learn about the movements and survival of bald eagles. When we band eagles we secure a small, individually-numbered metal ring or band on the legs of eagles to individually identify each bird. The birds wear the band for life. Eagles seem to get used to the bands like a ring on a finger. In the 1980s, we attempted to band all bald eagles in Maine and New Brunswick. For over a decade tree climber extraordinaire Barnie Thompson of Brewer, Maine climbed every eagle nest with young. Barnie climbed his last eagle nest several years ago when he approached his 70th birthday.
This June, tree climbers Bill Hanson and Chris DeSorbo (pictures above) are climbing nests in interior Maine as part of a study to evaluate the effects of mercury and organochlorine contaminants on eagles. (The eaglets at the web camera nest will not be banded.) Climbers use boot hooks, ropes, and safety equipment to climb trees. Although bald eagles are a large bird of prey, they do not defend their nest or attack the climbers. The adults often circle overhead and vocalize while the climber is in the nest. The climber gently places the 4 to 6 week-old eaglets in a canvass bag and slowly lowers them to biologists on the ground. Each chick is weighed and measured. Blood and feather samples are taken for the contaminants analysis. The metal bands are secured loosely around the leg and riveted in place. A red band with a large letter-number combination is a unique identifier for Maine eagles (other states and provinces each have their own assigned color bands) and aids with idenfication of birds from a distance. A standard U. S. Fish and Wildlife Service band has a unique number stamped into the band. The chicks are then hoisted back into the nest in the canvass bag. We gather prey remains at the base of the nest to learn more about eagle diets. The entire process takes about an hour.
Important information is learned from banding. Band numbers are retrieved from dead or injured eagles, and sometimes band numbers are read and reported by eagle watchers. Banding provides information on eagle movements. We've had eagles from Maine recovered or observed in as far away as Labrador and North Carolina. We've seen eagles in Maine banded from as far away as Saskatchewan, Nova Scotia, and Michigan. Repeated observations of banded eagles over the years are used to estimate survival rates of eagles. As part of my doctoral research, I read the band numbers from hundreds of eagles visiting winter feeding stations with a spotting scope and used the information to document survival rates for young and adult birds. Banding also provides information on how old eagles live in the wild. Recently we recovered an adult eagle 23 years after banding it as a chick in the early 1980s.
We do not band all the eagle chicks in Maine each year. Although biologists in some states routinely band all of their eagle chicks, we only band the birds for directed studies. We are no longer reobserving eagles at winter feeding stations to document survival rates. This summer, eaglets at selected nests are being banded in conjunction with a contaminants study.
Mark McCollough, U. S. Fish and Wildlife Service