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Ecology
Q&A about Bald Eagles with Peter Nye
New York Department of Environmental Conservation


Q. What is the eagle's favorite food?
A. Fish

Q. What are two things eagles like to eat alot?
A. Fish and birds.

Q. What is the average amount of fish an eagle can eat in a day?
A. They eat 5-10% of eagles' body weight.

Q. How much and what food do they eat?
A. Diet varies with season and with what is available (eagles are very opportunistic in their feeding habits), but fish is the number one food type followed by some birds (waterfowl), occasional turtles and other rarer items. Average daily food consumption is from 250-550 grams per day, or between 5-10% of an eagle's body weight.

Q. What are the Bald Eagles' natural predators?
A. Besides humans? Very few. Other bald eagles occasionly attack eagles and their young; racoons will sometimes kill young in the nest as will the occasional great horned owl.

Q. What is the lowest and highest temperature eagles can live in?
A. Another great question: bald eagles live in dramatic temperautre extremes, from hot deserts of Arizona and south to near the treeline in extreme northern Canada and Alaska. They seem quite adaptable to weather/temperature extremes.

Q. Is migration of the bald eagle based on availability of food source, temperature change, or what?
A. Mostly based upon available food supply, right on!

Q. How does the freezing weather affect the Bald Eagle?
A. It freezes up their water areas and forces them (usually south) to areas of milder weather for open water.

Q. What is the Bald Eagle migratory pattern?
A. Eagles aren't really migratory like some birds, but move only as far as they need to to survive (to find open water and food).

Q. Where do eagles migate?
A. Northern eagles typically move south to where they can find open water and food.

Q. Do eagles go back to the nest where they were born or to a different nest?
A. They do not go back to the exact nest where they were born (hopefully their parents would still be nesting there), but there is a concept called "site-fidelity" which means there is a strong attraction for a bird to return to the area where it was born. This "area" varies in size depending upon many factors such as available habitat and the existing density of eagles (i.e. is there room for more?). We have followed many young eagles who have subsequently returned to from 1-225 miles from where they were born to start their own nests.

Q. How many pounds of food does a Bald Eagle eat in a day?
A. Approximately .5 - 1.5 per day.

Q. Would an eagle eat other birds? I know that the eagle's favorite food is fish. I know that sometimes little birds tease big birds because eagles cannot manuver as well as the other birds, so could they eat them?
A. Very good and accurate observation dale. Yes they do and will eat other things, although fish are preferred when they can get them. They also like waterfowl. We check all of our nests each year when we climb up to band the eaglets, especially looking for prey (food) remains. We have found rabbits, muskrats, gulls, ducks, turtles, and lots of kinds of fish, just to name a few!

Q. What are the eagle's enemies?
A. An occasional racoon in the nest, or rarely a great horned owl in the nest (threat to nestlings only), but otherwise only human beings.

Q. What is the largest prey animal that they have been known to kill?
A. Good question. The key word here is "kill". Bald eagles are much more opportunists than killers, meaning that if they can get an easy meal without expending much energy (i.e. by killing something) they will do that. So, reports of bald eagles feeding on deer, whales, or other large animals, are usually because they found it/them already dead. Eagles are capable of killing geese, turkeys, swans (especially if they are already somewhat debilitated), and large salmon. I would not be surprised if they took any prey that was under about 3-4 pounds, which would be their max. No type of food item (meat) would surprise me either, except that obviously their favored prey is fish.

Q. In what kind of habitats do bald eagles live?
A. Almost exclusively aquatic based habitats, with forested, generally undisturbed uplands.

Q. How old are Bald Eagles when they migrate?
A. Soon after they leave the nest they begin (sometimes long distance) wandering--at about 6 months of age.

Q. How do scientists test Bald Eagle's navigational patterns?
A. We really haven't "tested" their navigational skills, but have deduced some of their pathways and patterns from banding and marking numerous birds and then receiving sightings or recovering dead birds. Also by affixing both conventional and new satellite radio telemetry devices to the birds then following their movements and analyzing where and when they go, deducing clues from their movements. For example from the satellite data, it's easy to see if an eagle is following a water course, where they stop for the night, etc. See above for more about migration behavior.

Q. Out of all the eagles that migrate, how many make it to their destinations?
A. Once they become adults, they have a high survival rate year to year, likely 90% or more.

Q. Do the same eagles come back each year to the same place?
A. Generally, yes they do, which is why it is so important to protect those areas eagles are known to use. You are lucky in maine, as you have a good population of eagles and some very dedicated biologists trying to save them. Your department of inland fisheries and wildlife can give you lots of additional info on eagles in Maine.

Q. If bald eagles do migrate, do they go to the same spot every year?
A. Generally (especially with adult birds) the answer is yes. That is one of the things our research is trying to answer using satellite tracking

Q. How exactly are satellite transmitters attached to an eagle?
A. As a "backpack", exactly like the one you might wear to school. Straps in front of and behind both wings are stitched together in the front.

Q. Do bald eagles fly in flocks or are they a solitary bird?
A. They usually fly alone, although some may follow others to feeding grounds, like from the morning roost, or when going back to the roost in the late afternoon.

Q. If eagles migrate south for the winter, why do they bother to go back north? Why don't they just stay in the south?
A. Great question. They have an inborn tradition to their general area of fledging, called "fidelity", which draws them back there. This instinct has probably evolved over thousands of years because if they were successfully born in a certain area, the chances of their success at nesting in the same general area are probably pretty high. It also helps keep the birds distributed. If they all decided to stay where they wintered, things would get pretty crowded in a hurry!

Q. Do bald eagles migrate from summer to winter?
A. Sometimes, especially when they nest in areas far to the north where these areas freeze over in fall/winter, so they must leave to find open water and survive. That is what this study. We think our eagle #32 summers in Canada and winters in southern New York state. We will find out as she migrates back to her nesting ground this spring.

Q. In what areas would bald eagles live in Nebraska?
A. Any areas near large water bodies or rivers with good fish populations (or waterfowl in the winter), especially those with little or no human disturbance. I think that Nebraska has a good number of eagles wintering there each year, but i'm not sure where--is the platte river in nebraska?? Check with your state Fish and Wildlife agency.

Q. Why do Bald eagles only congregate on the West Coast?
A. They don't. They are distributed throughout north america (except hawaii). The greatest number of nesting eagles in the lower 48 states occurs in florida !!

Q. Can bald eagles be found in every state of the United States?
A. Yes, except Hawaii.

Q. Can you expain why so many eagles overwinter in Alaska?
A. Because of the available habitat up there. Open water, plentiful food, and undisturbed habitats abound.

Q. How do the eagles find their way home?
A. If you mean home as in where they fledged from the nest, a variety of cues are used including mostly physical landmarks.

Q. We live in Florida where the eagles don't migrate, so how far north are eagles where they don't migrate?
A. Some eagles way up even in Alaska don't need to "migrate" or move because they can stay near the open ocean all winter and still get food. Believe it or not, some of your Florida eagles do migrate north following their breeding season; they have been recorded here in New York and even in eastern Canada. Why do they do this? Not sure, perhaps to escape the intense heat of summer. It is common for Florida fledglings to move north, but most of your adults do not.

Q. How do the transmitters (for satellie tracking) work?
A. They carry a battery and emit a specific radio signal picked up each time two orbiting satellites (23,000 miles above the earth) pass over their location. The satellites "read" the message sent by the transmitter and calculate its location (the latitude and longitude). The battery lasts for approximately 1-year. The satellite then sends this data back to earth to computers in Maryland, and I then access those computers from mine and get all the information. Then you guys get it - cool huh?

Q. Who do Eagles migrate with?
A. Eagles are believed to migrate alone, not in groups as some other birds (and even some raptors do), and not even with their mate necessarily, although as we learn more, that might change. For now, we've found male and female eagles tend to travel separately to (and from?) their breeding areas. This could be adaptive, so if something were to happen along the journey (an accident or just harsh conditions that might make it difficult for a bird to survive), both of the pair wouldn't be lost, since they are travelling separately and at separate times. We tracked one male to his nest in Ontario years ago, and know from that that he travelled alone and arrived their first; his female mate showed up a few days later.

Q. When do Eagles migrate?
A.This depends on where they are going (where they are from) ! They will generally begin migration when certain environmental cues tell them it is time to initiate the breeding cycle and move back toward their nesting areas. Cues such as day-length (amount of daylight) and hormones within the birds likely are at work. Of course, their timing for this move is critical; they mustn't move north until conditions (ie open water and food) will allow them to survive back on their breeding grounds.

Q. What determines when adults migrate or stay put? We live in downeast Maine and have an eagle nest on our land. This land has a conservation easement on it so the nest is protected! The nest is near a salt water bay. We know that this eagle pair stays here through the winter.
A. Excellent! You are SO lucky! Maine has been doing an excellent job monitoring and managing/conserving their eagles, and many states could take a lesson from what has been done there. Anyway, to your question. You are again correct in your observation about "your" local pair. We pretty much know that eagles that breed on or near areas of water that stay open year-round, like the ocean or fast-flowing rivers, remain at or near their breeding territories all year. The key to whether they move or not? FOOD ! If then can get all they need to survive through the winter, why leave?

Q. If an adult pair migrate, do they stay together through the migration? If not, how do they reestablish the pair bond when they return to the nest?
A. Our research to date indicates that mated pairs of eagles that do migrate, do not migrate together. I'm not sure why this is, but it could be adaptive (beneficial to the species over the long run) for them not to migrate together. This reduces the chances of both birds being killed for some reason along their migration, and may ensure that at least one of the adults survives and returns to the breeding territory to keep it going. Although we do observe what seem to be "pairs" of eagles together on the wintering ground, we do not know if this is generally the rule, or if mated pairs may not only not migrate together, but may also not use the same wintering areas. Again, this could be adaptive. This is also one of the ongoing research questions we are attempting to answer, and given enough time, we will.

After the eagles return to their nest, separately, they re-establish their pair bond by time-spent together and through distinct behaviors, such as beak-rubbing and aerial courtship flights, which are spectacular, and consist of flying together extremely closely, chasing and tumbling like fighter planes.

Q. If the wings are hurt and it can't migrate, how long would an eagle be able to survive?
A. It would depend on how badly injured the eagle's wings were. I suspect that if an eagle had a wing injury so severe it couldn't migrate, this would mean it couldn't fly well and it would not survive for long, perhaps a week or two at the most if it could not fly and get food on its own.

Q. Eagles have been seen in New Jersey. How many pairs are now living there and how far south have they migrated?
A. For the most accurate answer, I would contact the NJ Wildlife, Endangered Species people in Trenton. But here's my guess; about 20-30 nesting pairs. I also don't believe they are very migratory. I bet they stay in NJ around their nest site or not too far away most of the year; some (especially the immature birds) undoubtedly move down to the nearby Chesapeake Bay.

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, Vermon.
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?

Q: What specific type of fish do bald eagles prefer?
A: The easiest to catch! Usually this means fish that spend more time near the surface or in the shallows; ones that make themselves available to bald eagles, which hunt and capture fish near the surface of water. The species involved are not as important as the niche they occupy, and vary with the region. Here in New York, along our Hudson River, as just one example, breeding eagles take a lot of American eels, which can often be found near the surface and in shallow waters, especially when the tide is low in the river.

Q: What are the bald eagles' enemies besides people?
A: Not many. Humans and our activities are definitely the biggest problem for eagles. But, occasionally other bald eagles will be a problem, fighting each other, especially over prime breeding territories. Raccoons can also be a problem to nesting eagles. Attracted by fish scraps and smells at the base of nest trees, raccoons have no problem scaling trees 80 feet high or higher to investigate, sometimes killing the young eaglets in the nest. This has happened in many places, including here in New York and in Massachusetts.

Q: Are there bald eagles west of the Rockies?
A: Absolutely! Bald eagles are found in all 48 continental states as well as Alaska. Only Hawaii doesn't have bald eagles. The Pacific Northwest has a very large bald eagle poplulation, with hundreds of pairs breeding in Oregon and Washington. If you go back in the Journey North archives, you'll find some wintering eagles from Washington State that were tracked to their breeding grounds, just like we are doing here in New York. What major difference can you find in west coast versus east coast movement patterns?

Q: What is the bald eagles' migration path?
A:
That's one thing we're trying to find out! The answer varies due to many factors:

  • where the birds are from
  • where they are wintering
  • their age
  • the season

Some eagles don't migrate at all. If they live in an area where they can survive all winter (one with plenty of open water and food), they will stay close to their nesting area and not move far at all. If they do have to move to find open water and food, generally they will only move as far as they need to find a suitable over-wintering area that meets their needs. Young eagles, not yet adults, may move in more random directions than adults who have developed strong habits, returning along the same routes to the same wintering and nesting areas year after year. Movement pathways also depend on the season. In the spring, adult eagles departing their wintering area usually follow a pretty direct route to their nesting area, wanting to get back quickly to reestablish their territory and initiate breeding. In the fall, these eagles are in no such hurry to get back to the wintering area, and take a more leisurely route, not as direct and taking longer.

Go to the Journey North archives and investigate these things for yourself. See how different birds routes differ, and compare the spring and fall routes of the same bird. Also, take a look at the route followed by the same bird in different years and see what you can discover: this is what we biologists do!

Q: We like the maps showing where the Bald Eagles travel. We were curious if you have noticed any patterns in all of the years you have been showing the bald eagles' travels.
A: Absolutely! The most important finding we've had, especially with adult eagles, is that they exhibit nearly perfect fidelity to their wintering sites. That is, they return to their same wintering site, over and over again, winter after winter. That obviously tells us these areas are extremely important to them, and must be protected if we are to ensure they continue to use these areas for many years to come. Such use of research findings is called applied management, and is very important to keeping these populations around.

We've also seen differences in routes and timing, in spring vs fall migration. We are constantly learning, and using that knowledge to help this species. We will be preparing a scientific paper with our results as soon as we have enough eagles tracked to make meaningful assumptions.

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."

Q: We live in Colorado and would like information on the migration path the eagles take in the mountain states and west coast.
A: Colorado hosts a "winter" eagle population much larger than its summer breeding population, and most of these 500-1000 birds hail from Canada. One of the major wintering areas for bald eagles in CO is the San Luis Valley in south-central CO. Back in the 1970's and '80's an eagle researcher named Al Harmata captured wintering eagles in CO and studied their migration. You might want to look up his work (Ph.D. thesis, 1984, Montana State Univ., Bozeman). I believe some of his birds were tracked back to summering grounds in the Northwest Territories of extreme northwestern Canada and Saskatchewan. I would guess based on other studies and banding records that other CO wintering eagles come from British Columbia, Alberta, and perhaps Manitoba. Also, a considerable amount of work on bald eagle migration in the western United States, particularly in Washington State, has been conducted by Jim Watson of the Washington State Department of Fish and Wildlife.

Q: Are there Bald Eagles in Rolling Meadows, Illinois? If so, would they be found in northern or southern Illinois?
A: There are eagles in Illinois! It has been reported that as many as five thousand Bald Eagles winter on the river between Cairo, Illinois and St. Paul, Minnesota, tending to concentrate near several large dams. I find that figure a bit high. But there is no doubt that the Mississippi River, in particular, with extensive open water (due to hydro-electric dams) and fish they provide, is a major attraction to wintering Bald Eagles. And, of course, you've got that famous "Quad Cities" area along the River, with annual winter concentrations of eagles.

Q: Why do the maps focus on the Northeastern part of the United States? Today, at the Heard Natural History Museum and Wildlife Sanctuary in McKinney Texas, we saw a Bald Eagle flying high, over our Sycamore Trail.
A: The maps focus on the Northeast United States because that is where our eagle research has focused, and so you are seeing only a small piece of eagle behavior from one part of our country. Eagles, both wintering and breeding eagles, are found in every state except Hawaii. Many people have studied eagle movements over the years in different places around the country, but now, you are seeing just the Northeast United States research.

Q: Why do we have 20-30 Bald Eagles on Lake Macatawa in Holland, Michigan? This has not happened before.
A: I have to guess here, based on just the little bit of information you gave me. I assume you mean they are here now in the winter, not as breeding birds (or you would have noticed them many times before each summer). I wonder if your lake is open water (or partially so) or if it is frozen? I can tell you why the eagles are there, almost without question; because they are finding food there! This could either be from carrion (dead animal carcasses such as deer), or perhaps a fish-kill, or a particularly good concentration of waterfowl.

Q: I read information that stated eagles fly into storms, use the winds of the storm to gain altitude, and that they rise way above the storm. Could you direct me to a reliable source that would confirm it or deny this information?
A: I have never heard of this behavior exactly as you describe it. This sounds like stretching or misinterpreting what eagles do. Eagles definitely do use the winds (and some quite strong), as well as "updrafts" coming off hills and mountains. This helps them to gain altitude and set them up for a long, soaring flight to another location, especially when they migrate great distances north or south. This behavior saves considerable energy, and the eagles hardly have to flap their wings.

Q. How many Bald Eagles are there? (1998)
A. A 1975 estimate of the total bald eagles in the world (since they are only found in North America, I could say North America) was between 35,000 and 60,000! Most of these are in Alaska and Canada where bald eagles are not endangered. To give you an idea of how the population has grown in the lower 48 states, in 1963 there were 417 breeding pairs known, and in 1994 that number was up to 4,452!

 


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


 

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