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Bald Eagle Facts
Q&A with Peter Nye in 2002
New York Department of Environmental Conservation


Characteristics

Q: Do the bald eagles have a special technique for breathing when they fly so high?

A: Good question! This sent me to the bird physiology books myself! In reality, eagles tend to use very little energy "when they fly so high". Even though they can reach altitudes of over 10,000 feet, they are usually soaring to these heights, and taking long glides to cover ground, then soaring up again and repeating the process. By flying in this way, there body is really not demanding much oxygen, not any where near as much as when they are much closer to the ground and expending considerable energy flapping their wings. So, no, they have no special adaptations for breathing at high altitudes.

Q: Do eagles see in black or white or color? Do they dislike the color red?

A: I knew I had seen a very thorough treatment of eyes and sight somewhere, so below is what I found at this web-site: "All eagles are renowned for their excellent eyesight, and the bald eagle is no exception. They have two foveae, or centers of focus, that allow the birds to see both forward and to the side at the same time. Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding, or in flapping flight. This is quite an extraordinary feat, since most fish are counter-shaded, meaning they are darker on top and thus harder to see from above. Fishermen can confirm how difficult it is to see a fish just beneath the surface of the water from only a short distance away. Young bald eagles have been known to make mistakes, such as attacking objects like plastic bottles floating on or just below the surface of the water. Bald eagles will locate and catch dead fish much more rapidly and efficiently than live fish, because dead fish float with their light underside up, making them easier to see. Eagles have eyelids that close during sleep. For blinking, they also have an inner eyelid called a nictitating membrane. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while it is over the eye. Eagles, like all birds, have color vision. An eagle's eye is almost as large as a human's, but its sharpness is at least four times that of a person with perfect vision. The eagle can probably identify a rabbit moving almost a mile away. That means that an eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles from a fixed position."


Life Cycle

Q: Could it be possible that a twig I saw an eagle break from a branch could be used for building a nest? After observing a bald eagle perched in a tree along a river for over 20 minutes, I observed it fly to a tree 10 yards away and break off a branch in its talons and fly off. This occurred in Iowa in early February. Two eagles have been seen in this area throughout the winter.

A: Absolutely it could! I assume the eagle you observed was an adult. Immatures may occasionally do this for play or practice, but it is typical behavior for adults prior to and during nesting. What you saw could be a local breeder getting its nest "ready" for the breeding season (here in NY we have some pairs who begin decorating their nests in early February, and I'd bet Iowa would too), or, it could have been a wintering bird just fooling around and "feeling its oats" in anticipation for migration and nesting back up north. Very rarely, some wintering birds will actually build a nest on their wintering grounds during the winter season, even though they have no intention of staying and using it (they just might be very stimulated breeders!); we have seen this in NY, and the pair return to their "winter" nest and decorate it and sit in it each winter, before leaving for their "real" nest somewhere up north in late March. The fascinating thing to me about what you describe, and which I've also seen, is how the heck the eagle "knows" that the stick they fly at and hit in mid-flight will give way! It's got to be a good decision between flying force at the stick to break it off versus not sort of flying yourself into a brick wall so-to-speak! How do they know ahead of time the stick they've "chosen" will break off ?? (that's a rhetorical question, not a challenge one!). Anyway, that is a neat thing to observe! I would look for a nest in the vicinity!

Q: Are eagles courting when they interlock talons as they soar through the air?

A: With wildlife, it is often hard to determine reasons behind behaviors we may observe. Talon-grappling and tumbling are frequently observed behaviors; seen between all combinations of eagles. Meaning, between mated adults, un-paired adults, adult and immatures, immatures with immatures, etc. These are also likely "unions" of any-sex combination of birds. That variety of participants, tells me right away there is no one answer to what this behavior is for, but rather, that it happens for a variety of reasons. Three come to my mind immediately; pair-bonding, aggression, and play. So, yes, I believe paired adults do it as a "courting"/bonding activity. We also know from observations that these represent very aggressive encounters, where sometimes, one or both of the participants are killed (sometimes they cannot "un-lock" and crash to the ground together. The most often I see this, is with and between immatures, and I'm convinced it is both play and learning (flight capability). I do believe that eagles get enjoyment out of certain activities, which could be called play, such as when they chase each other in flight, tumble, roll, etc. As with humans, I think immature bald eagles are more prone to "play" than adult birds, who always seem to have something deliberate to do :-)


Ecology

Q: Does temperature affect when and how far eagles migrate?
If the temperature gets very hot, warmer than normal for this time of year, will that affect the Bald Eagle migration? Will the eagles migrate faster or travel further than usual?

A: Mild (warmer) weather, which translates to more extensive open water and hence more food, does affect the movement and wintering locations of some eagles. Despite this, I suspect some eagles, especially older adult birds used to going to the same, successful wintering area, still will go to their traditional site even during mild winters. We have also seen the very mild late - winter periods, such as this winter, cause birds to "move out early". I would say overall, they stay pretty much with movement based on day-length, thus calender time, but milder weather sure does allow them to move around a lot more. I don't believe it would affect the speed of their migration.

Q: Since bald eagles spend time in warm and cold climates, do they like it better in the heat or the cold?

A: That's a hard one, because you are asking me to predict what an eagle "likes". You are right that they are found from the hot, hot deserts of Arizona to the very cold climes of northern Canada and Alaska. I don't think it is so much of a question of what they "like" or don't like, but rather which condition is harder (more stressful) on them, This, also, is tough to say, since they do succeed (reproduce successfully), under a wide variety of such conditions. My own feeling, based for one thing upon raw numbers in very "hot" spots versus colder spots, is that the extreme heat is deadlier for them. You (they) can't shed excess heat easily, and even here in NY we have had nestlings expire due to hyperthermia, but they can maintain body temperature given enough fuel (food). Once in a while prolonged periods of wet weather or snow can be a factor on nestlings also. You'll find the vast majority of bald eagles living out their lives in temperate to colder climates.

Q: Do the same eagles winter in the same place each year? Or would Kentucky' eagles some winters migrate to New York?

A: Our years of studying wintering eagles in New York have shown us that, indeed, there a high "site-fidelity" by the birds, especially older birds. Young eagles may wander around a bit more during their immature years, before they too settle on an area to their liking which becomes their habitual winter home.

Q: Do the eagles that winter in Kentucky go as far north as the eagles that winter in New York? I go to Land Between the Lakes in Kentucky each winter to see the eagles.

A: Excellent question. I am aware that good numbers of eagles can be seen at LBL each winter, but have never given much thought to where they come from. Let's do some "on the spot" thinking about this. We (in New York) have captured and banded well over 100 wintering bald eagles over the past 20 years (as of 2002). Most of these have turned out to be birds that indeed do winter in New York, but we have also captured some that were obviously in transit between places (note eagle E63 that we caught last year, but which we found out this year wintered in Maryland at the northern end of the Chesapeake Bay). However, E63 is by far the exception, and represents the furthest south any of our winter-captured eagles have been recorded. As you also know from studying the JN data over the years, our wintering eagles come from and thus represent a large geographic area of eastern Canada. It would seem logical then, that if some of these eastern Canadian birds migrated that far south, we would have snagged one by now and seen this. Therefore, I would conclude that, no, the LBL birds do not hail from the same northern territories. Likewise, from banding and radio-tagging studies conducted over the past two decades in other states such as in TN, MD, VA, FL and other mid-east and southern states, we do know that birds from these areas use the LBL. Although I don't believe any radio-tracking studies of these LBL birds has been done, my best guess is that birds that winter there come mostly from nearby breeding areas and from the greater Cheasapeake Bay population. A great contact for information on these eagles is Mr. Bob Hatcher of the Tennessee Wildlife Division, who is very familiar with those birds and that area; I'm sure he can give you lots more information on this.

Q: Do the eagles migrate in flocks? What is the typical size of a group of eagles?

A: No, eagles migrate alone as far as we know. Some breeding pairs may migrate together, but we do not know this at this point; this is a question I would like to answer using our satellite-telemetry project you study through JN. How do you think we could determine this? This is not to say that on a given day in the fall or spring, many eagles might not be seen moving south or north during the same day (for example some hawk-watches may report 50 or more eagles moving by in one day). This does happen, but it is related to the weather conditions (suitable days for migrating), which facilitate many birds moving, but not necessarily as "groups" as we see in waterfowl like geese.

Q: Would it be typical to see 10 eagles together in a group?
There was a sighting of 10 eagles in Vermont in the same place. We thought they travelled alone and didn't expect to hear that they were in a flock.

A:
The answer kind of depends upon the time of year! It would be very unusual to see such a number together during the breeding season, since eagles are territorial and typically space themselves out as breeders, so you would only see a couple of adults and their young "together". I have to say though, that in some places where eagles are extremely abundant, such as in Southeast Alaska, one could see such a grouping of immatures and non-breeders in an area where no nests are (and thus are "safe" from territorial interactions). However, I can assure you, this is not the case in Vermont! I assume the sighting you mention was between December and March, and likely along a major river or lake, and these were wintering birds attracted by some food source. During winter, eagles are gregarious (will be in groups and tolerate each other) by necessity, to share common food sources. In summer, suitable habitat is less limited and thus they can afford to be more solitary and territorial. No nesting eagles that we know of yet in VT (as of 2002), although keep the faith; one will be there soon!

Q: We want to know if eagles ever stay in an area for the whole year?
We are hoping that eagle #E47 stays in Ferrisburgh, Vermont!

A: Yes, eagles do sometimes "stay" in an area all year round. I'm sure you can figure this out with a little thought. Why would they stay or move? Knowing that, where might you expect eagles would not "move" ?

If they can fulfill their life-functions/needs, why move? For eagles, this means open water and food; if they can find enough all year-round, why leave. In such places, like Southeast Alaska and other coastal areas like Maine, Chesapeake Bay, etc., eagles often do not need to move and don't ! Even in some places along our Hudson River here in NY, if we have a mild winter and the Rriver doesn't freeze up solid and the eagles can find what they need, they will stay by their territory year-round. This seems like a pretty smart strategy to me; rather than being a determinant migrant (they go regardless of the weather and food, like ospreys do), eagles appear to be opportunistic migrants, and adapt their movements as needed. For example in your area, the winter was very mild this year (2002) and most of Lake Champlain was open all winter long, attracting and keeping wintering eagles there. If you study the JN maps, you'll see a couple of our birds "short-circuited" (didn't go all the way south to where they were previously caught) and spent a lot of time up on Lake Champlain. Concerning E47, again, you can answer that one! We caught her a year ago February; where did she go in spring? What do you think she'll do this year?


Conservation

Q: Has there ever been a tagged eagle that has been shot down by a hunter?

A:
Yes, unfortunately. We have found many of the eagles we have banded and released dead due to gunshot, and last time I checked, that was one of the major causes of mortality we see (others include vehicular collisions and other trauma). We need to be careful of the use of that term "hunter" though. Although, technically, anyone pursuing a creature to kill or capture it is "hunting", the hunters we generally think of today are sportsman who are very concerned about all natural resources and are some of the first to insist on their protection. People who shoot eagles and hawks are definitely not the hunters I associate with the sport of hunting. Fortunately, we have come a long way in educating people about this and far fewer eagles are shot these days than 10-15 years ago (as of 2002). This is not a population-limiting factor, as much as it does anger me.

Q: Could 5th grade students do a community service project to benefit eagles? Our school is located in Pella, Iowa. We have a large lake/dam (Lake Red Rock) that attracts and feeds bald eagles each winter. Any suggestions?

A: Lots of different ways to help eagles: Two things come immediately to mind in your case. One aspect would involve public education about eagles and their needs. Perhaps develop some signage or a pamphlet that explains something about the life history of the bald eagle, why it comes down to Iowa and your lake each winter, how important that lake and food source is to those same birds and their young each winter (based on knowledge we have learned about site-fidelity; you could cite your Journey North studies!) , and how people can enjoy/view them while at the same time protecting them. Your class could make up a pamphlet in conjunction with your local Town or Conservation people, get some local business or your school to print up a bunch, and get them distributed each winter at key sites around the lake. Here again, either your class/school or the Town/County could make some kiosks for such pamphlets, and even keep them stocked. In conjunction with this "educational" effort, I'm thinking it might be very important to identify and protect the most important areas around the lake that the birds use, and then post signs around these areas, protecting them from disturbance by people.

Second, I am not sure how large your lake is or how much is known, but it might also be very useful for your science class to run a "monitoring" program on the lake next winter. Set up a monitoring schedule with some students and parents or teachers with cars, where you observe the eagles, say once per week throughout the winter, to determine when they arrive, how many there are, and importantly, plot out their locations where they perch or roost around the lake. This information could be used to help protect your local birds and make sure they can return year after year to your lake. Don't forget to really investigate WHY eagles are coming to Lake Red Rock : which had to be FOOD. There must be a power plant, which maybe is putting out dead or dying fish ? What kind? Once you know that, what is happening with that particular fish population? Anything that could harm it? How would changes in operation of such a power plant affect your visiting eagles? What if they shut down the plant, or what if they installed a "trash-rack" which precluded entrainment (look it up!) of fish through the plant?

What if you state fisheries people introduced a predatory fish for anglers to catch, that potentially could wipe out or affect the fish population the eagles are using and need? It is important to not take anything for granted; question local officials and leaders (even your conservation people) to make sure they understand the needs of "your" eagles and are incorporating those needs into their thinking and planning. If you don't, maybe nobody will ! Maybe just do a winter of monitoring of your lake, put your findings into a letter to your state or county officials, and ask them specifically what conservation plans they have for your Red Rock Lake eagles to ensure they continue to use the lake and find it suitable habitat. Sorry to go on and on with this response, but, this is really a key question and need, which applies to ANY bald eagle habitat any of you know about and cherish anywhere in North America: what are these important habitats and what is being done for them? Are they "safe" ? Local oversight of such places is crucial; keep your eyes open and keep involved! The most important message we need to get accross to the "public" now, especially since eagles seem to be doing so well, is that we still need to identify their most important habitats, and protect these so that they remain available to them for use for many decades to come, even long after we are gone! Good luck!

Peter E. Nye
New York State Dept. Environmental Conservation
Division of Fish, Wildlife and Marine Resources
Delmar, NY
Spring, 2002

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