Bald Eagle Facts
Q&A with Peter Nye in 2004
New York Department of Environmental Conservation



Q: Does an eagle fly aerodynamically like an airplane?

A: All birds share aerodynamics of airplanes (actually it is airplanes that have "learned" their aerodynamic lessons from birds!). Bird wings are designed to achieve lift through differences in pressure as air moves over and under the wing. (See "Bernoulli's principle of flight.") Birds, including eagles, also have hollow (yet very strong) bones to decrease total body weight and help in flight. Unlike many other birds, though, eagles are fairly heavy, bulky birds. Because of this, they need a lot of room and a lot of energy to take off, not unlike an airplane. They are not birds designed for quick flight and maneuvers. Rather, they really shine as soaring birds, using their large wings, once airborne, taking advantage of air currents and natural thermals, to float almost effortlessly at great heights and over long distances.

Life Cycle

Q: How long can an eagle live? How long do they usually live?

A: That depends on what might happen to it! Unfortunately, many eagles don't live out the length of the life they are biologically capable of, due to a variety of factors. Contaminants, shooting, traps, cars, trains, wires (electrocution), collisions, and even other eagles, can cut an eagle's life short. Barring any of these events, an eagle is capable of living for 30 or more years. We captured an eagle in 2001 that we had banded in 1976, a female who was still breeding. Eagles held in captivity undoubtedly live longer than those in the wild, since they don't have the stresses that eagles in the wild face (such as finding food everyday and defending their territory. Two reports exist of captive eagles living 47 years.

Q: How long do the young stay with their parents after fledgling?

A: Depends on how "independent" they feel! Some youngsters "bust-out" quickly, thinking they are fully capable of being on their own. In many cases, they pay for this with their lives during their first fall and winter. On average, I'd say they spend 4-12 weeks in the nesting territory post-fledging, the time during which they learn to hunt and fly.

Q: Do young eagles learn to hunt from their parents or are their skills innate?

A: An excellent question. Young eagles from wild nests develop their hunting skills on their own, but spend considerable time after they fledge watching their parents and undoubtedly learning by watching what the adults do. The actual skills involved are learned by trial and error, I'm sure. Much of the hunting skill (or at least the drive to hunt) is innate, as our hacked eagles were fledged into an environment without adults around to "teach" or "show" these young birds. Yet, these birds, again through trial and error, learned to hunt for themselves and survive. We felt it was important to continue to provide food at our hacking towers after the eaglets fledged, to give them a source of food for as long as they needed it. Eventually, each eagle at it's own pace, these young birds stopped using our offerings and began foraging on their own. Similarly in the wild, the adult parents will continue to provide food for some time after fledging, while the newly flighted birds hone not only their hunting skills, but there flying skills. On average, I would say it takes about 4-12 weeks for young eagles to start hunting successfully. True, fully refined, specialized hunting skills, probably take years to develop.


Q: Can eagles get sick from eating prey that is sick?
Can the bald eagle contract the flu that some chickens are getting if they get a dead carcass from someone's yard and eat it? If the eagle eats an elk with chronic wasting disease can it get that disease as well?

A: I turned to our noted Wildlife Pathologist here in New York, Ward Stone, for help in answering this one. Ward writes: "There is a strong possibility that some exotic avian flu strains would be pathogenic to bald eagles and other raptors. We certainly do not want to establish the Asian strains we hear about killing chicken and other birds in this country. Other avian flues are always present in this country and are not at all rare in our wild ducks where they cause little-to-no trouble, and these do not pose a threat to eagles." Regarding chronic wasting disease, "There is no evidence that the prions of CWD cause disease in eagles or other predators and scavengers. "It will bear further study, however. It is likely that the normal prion structure of deer and eagles is so different that the abnormal protein of CWD can't make the taxonomic leap."

Other Questions

Q: Does an eagle "forget" how to hunt after being fed in captivity?

A: I don't believe so, not if they were brought into captivity after they had been fully flighted and independent birds. What you heard may have been more along the lines of birds in captivity losing their muscle tone and strength, often requiring flight-training on a creance (long leash) to redevelop their muscles.

Q: Why don't eagles nest in our state (Vermont)?
Eagles nest in New York, right across Lake Champlain from us. Why don't they nest on the Vermont side?

A: That's a great question Hannah, and one all of us "eagle biologists" in New England have been asking ourselves for many years now! As I said in answer to another question above, Vermont is currently the only state in the Northeast that does not have nesting bald eagles. Even the tiny state of Rhode Island now has nesting eagles! The answer, I believe, lies with simple numbers, not in habitat. From what I know of Vermont, there are certainly places where eagles could nest and thrive. I think it is simple a matter of numbers; there isn't yet a sufficient density of eagles in the vicinity to "spill over" and start colonizing Vermont. See my response to the question above about hacking and nest establishment. Once a few more nests are established in the region (either in New Hampshire or nearby Northern New York on the other side of Lake Champlain), this will set the stage for colonization of Vermont. I will predict you will have nesting eagles in Vermont within five years (of 2004)!

Q: How do you interpret the eagle behavior we witnessed?
Several years ago, my son and I witnessed two Bald Eagles in the top of a cottonwood tree. This would have been the second week in January, and we were in northern Missouri. The eagles seemed to take turns flying from their perch to the ground, where they would retrieve a broken branch. They would then fly back up to their perch and at this time release the branch. Usually the branch would bounce off the limb where one of the eagles was still perched. They continued this activity for the next half hour, and were still doing this as we quietly left. I have looked in several reference books and have yet to find an answer to explain this activity. Do you know what they were doing?

A: It sounds like this might have been associated with pair-bonding and preliminary to nesting; perhaps trying to entice a mate.

Q: Does relocating eagles affect their migration path?
In your biography you describe how you successfully reintroduced bald eagle nesting pairs to New York vacant habitats through the "hacking" method from eagles from Alaska.

A. I doubt it. The "hacking" program is based on a well known concept in avian biology called "fidelity", and specifically in this case fidelity to birthplace. In the case of hacking, we rely on this concept to predict that young eagles brought to hacking towers at an early enough age, believe this is their nest site, and orient to this site/area once they fledge. In a nutshell, we believe (and now know)that eagles that fledge from our hacking sites, think this is "home", and return to this general area once they reach sexual maturity for their own breeding. You are correct in your references to fledgling eagle behavior; they do indeed "wander" upon leaving the nest, in apparently random patterns. We know that some of them do return to their nesting areas or hack towers in years following, still as immature eagles, probably as a kind of "re-orientation" of where they came from. When there is still an active adult pair nesting there, in all likelihood, they chase off the now unwelcome youngster. This prevents possible inbreeding and also competition for food resources. I am sure that whatever "migratory" or movement patterns hacked eagles display, are not affected by their translocation.

An interesting finding from all of our years of translocating and banding eagles here (nearly 1000 now!) is that males appear to "home" closer to their natal (fledging) area than do females. In one analysis several years ago, we found that males, on average, remained within 60km of their natal area when they began nesting while females ranged up to 160km, on average. Such a gender-biased trend has also been reported in other species of raptors.

Q. Is there a way to help the Bald Eagle develop immunity against the West Nile Virus in Colorado?

A: This question is not specific to Colorado. While bald eagles clearly do contract the WNV, and several are suspected to have died from it, there doesn't appear to be any sure-fire way to innoculate eagles or other raptors against this. Folks have been experimenting with various vaccines, and there is one for horses that has been tried on birds.

This vaccine has been tried with caged/captive birds, but the efficacy (effectiveness) of this vaccine is far from certain. I know of one bald eagle that died in captivity despite being given the vaccine. At this point, there doesn't appear to be a quick and effective measure, especially for wild birds. The idea of treating large, highly mobile populations of wild birds is difficult at best, and likely not possible.

As with most such things, scientists believe that "nature will ultimately take its course, as it has for centuries." Under conditions of continuous exposure to the virus, eagles and other birds will slowly develop resistance to this particular strain and as birds survive the epidemic they will pass on their West Nile-resistant traits to future generations and, over time, will become resistant.

Q: What, if any, safe guards are you using against the West Nile Virus and the bald eagle?

A: We are not using any particular "safeguards" here. We have been collecting blood samples from some of our nestling eagles during our banding visits, just to check and see if any have been exposed; so far none have come back positive. See my response to above question; over time, the concern for this virus, and its effects, should subside.

Q: If someone is putting radio collars on Eagles in our area, how may I help?

A: First, understand that radios we put on eagles are not "collars" as you might think of a dog collar. Such radio attachments are used on some animals, like bears and moose. The radio transmitters we put on eagles are in a "backpack configuration", just like you might wear a backpack. I see you are from Vermont. You are in luck! Although there are currently no nesting bald eagles in Vermont (strangely, the only Northeast state without any nesting bald eagles), the Vermont Fish and Wildlife Department in cooperation with the National Wildlife Federation up there will be hacking some young bald eagles on the shores of Lake Champlain this summer, and they will all have radio transmitters allowing biologists to follow them and make sure they are doing ok. This is an attempt to establish some nesting birds in that region.

Peter E. Nye
New York State Dept. Environmental Conservation
Division of Fish, Wildlife and Marine Resources
Albany, NY
Spring, 2004