Students' Questions and Experts' Answers
Contributed by Eagle Expert Peter Nye
thanks to Eagle-Eye Nye for providing his time and expertise in responding
to your questions!
How much can a Bald Eagle lift?
Bald eagles generally weigh between 4 - 6 kilograms (I'll let you look
up the conversion to pounds !), although some have been found both below
and above this range, with some Alaskan eagles recorded with weights of
well over 7 kg. Female eagles are the larger and heavier of the sexes.
Now that we now how much eagles themselves can weigh, we can use that
to define how much they can "lift". Of many prey items found
in nests and weighed, a good general rule seems to be that eagles can
carry up to half of their own weight. This obviously means female eagles
are able to carry more larger prey than the males. Sometimes, eagles have
trouble judging the weight of prey. I've witnessed eagles in Alaska "lock
on" to a large salmon, obviously heavier than could be carried away
in flight, and the eagle is very capable of floating and "swimming"
to shore with its prey, rather than give it up. Then, dragged up on shore,
the feasting begins.
In the wild, how long can Bald Eagles bare young?
The life span of eagles in the wild is generally around 30 years.
Actually, little is known about the reproductive life of eagles as they
age, due to the lack of known-age/banded birds and intensive observations
of same. I can tell you that we captured one of our local breeders at
her age 25 years, and she went on to breed and raise young successfully
in her 26th year. It is my opinion that eagles are probably productive
until they die. It would be mal-adaptive for adult eagles to remain in
the population as non-contributing members. More often, I believe what
happens is the aging/unproductive bird is actually killed and replaced
by a younger, more productive and fit adult.
Heyworth High School
What did the Bald Eagles Evolve from? Who are their evolutionary ancestors?
You mean besides reptiles ??
According to Mark Stahlmaster's wonderful book on bald eagles,
the "sea eagles" of which the bald eagle is one of eight, began
evolving tens of millions of years ago from a group of birds known as
kites, which share many of the same characteristics of the sea eagles
(fishing, scavenging, breeding). He states these ancient kites provided
the genetic framework for an ancient sea eagle, which eventually evolved
into eight separate sea eagle species. According to Mark, there are fossil
remains of this ancient sea eagle at least 25 million years old. Although
we don't know precisely when the white-headed sea eagle (our bald eagle)
evolved, there are numerous fossil remains, some from North America as
long as one million years ago. Bald eagles are in the order "Falconiformes"
(including most raptors except owls), and the family "Accipitridae",
which includes 205 species of eagles, hawks, kites, old world vultures
and harriers. Four groups of eagles are recognized, containing 59 different
species of eagles worldwide: Buzzard-like eagles (Harpy Eagles), Fish
and Sea Eagles, Snake Eagles, and Booted Eagles. Our golden eagles are
members of the "booted" eagles.
Where were the first sightings of the Bald eagle?
As mentioned above, bald eagles have been found in fossil remains in North
America more than one million years old, including in tar pits in California
and frequently in Indian middens throughout the continent. The bald eagle
is exclusively a bird of North America. I'm not sure what you mean exactly
by "where were the first sightings", but I would bet that as
early man crossed the land bridge from Asia through Alaska and migrated
south, that they encountered eagles along the coastal areas not covered
in ice. I'm sure native Americans living in New York and the east frequently
encountered bald eagles, and surely captured and killed many for food
and spiritual purposes. Later than that, on his journey up the Hudson
River in 1609, I'm sure Henry Hudson was privileged to observe bald eagles
along the pristine shores of our Hudson River.
We know that dog life spans are 7 years to 1 human's life span, so what
is the eagle's to a human's?
To answer that we have to explain how long eagles can live.
In captivity (a more coddled life...), bald eagles have lived well into
their 40's. But in the wild, their life is undoubtedly much shorter, either
cut short by human beings, by other eagles, or by the rigors of their
In the wild, we believe eagles live around 30 years. Therefore, I guess
you'd say an eagles life is about 2.5 to each human year, based on our
current average life expectancy.
How long do Bald Eagles live? How old are A20 Golden Eagle and V98 Bald
See answer above.
Golden eagle A20 was about 2 years old when he was captured, and is now
5 years old.
Bald eagle V98 was a full adult when we captured it last March, so it
was at least 5 years old then. We cannot say how old an adult is once
it obtains its white head and tail (adult plumage), unless it was previously
banded. We recently trapped an eagle we had banded in 1976, at 25 years
Sappington School, LEAP program
We have been talking about environmental things that hurt the habitats
and food supplies of animals. What about bird eggs? How many healthy Bald
Eagle eggs were laid in the year 2004? How many survived?
In New York State in 2004 we confirmed 84 breeding pairs of bald
eagles; 79 of these pairs laid eggs (exact number unknown), and only 66
of these pairs were successful (fledged young). A total of 111 young were
fledged, meaning that, on average, each of the 66 pairs fledged 1.68 young.
Biologists believe that mostly, bald eagles lay two eggs, even if only
one eaglet is hatched and fledged. Of course, without numerous intrusions
into the nests, we can't know exactly how many eggs are laid by every
pair. Of the 13 of our 2004 pairs that failed, they laid at least 13 eggs,
and possibly as many as 26. About 5 percent of the time, eagle pairs will
lay 3 eggs. In addition, we recovered 10 unhatched eggs from 8 of the
66 successful nests. Every time I visit a nest to band young, I dig around
the nest cup in search of buried, unhatched eggs. These are valuable for
contaminant and shell-thickness analysis. So, at least 23 more eggs were
laid, and probably more, than the 111 young we had this past year. Biologists
believe that if eagles produce at least 1 young per breeding attempt,
that the population will do fine and not decrease. Did you follow all
I have noticed in various books with photographs of Bald Eagles that their
eye color can vary. I've seen blue, yellow, and brown. Why?
Generally, eagle eyes are pretty consistent in color.
Nestling eagles eyes are nearly black. Juvenile eagles (first year birds
just out of the nest), have brown eyes (which can vary in how light or
dark they are, but usually they are pretty dark).
As they become immature eagles (ages 2,3), their eye lightens to a light
brown. As they get near sexual maturity (age 4,5), their eye turns yellow,
and again can be in various shades of lighter to darker yellow, but usually
quite light yellow. I believe that the darker eye color of juveniles and
immatures may be a defensive mechanism, not seen as the threat yellow,
adult eyes might be. Similar coloration and gradual color shift to lighter
and brighter are found in the bills of bald eagles as they age. I've never
seen blue eyes in eagles though !
Dee Dee Bach
For 3 years I have observed a nesting pair of Bald Eagles near my home.
The pair has been nesting for 15 years in the same location.
Last year the male crushed one egg in mid air. The other made it to a
first flight only, never to be seen after a few days. It stayed in a tree
near the nest, but then died. Do they reach a point like humans where
they cannot bear young or was this just coincidence?
The pair is currently nesting. She laid the eggs on 2/28.
Thank you for any information you can provide me.
I'm curious to know where you live ! Judging by the February 28th egg
date, you must be in PA or south....NJ ?
The mid-air egg-crushing you mention is quite strange and begs another
question. Did this pair raise/fledge any young the same year? I think,
if I'm reading your question correctly, you are saying one young was fledged.
Often, one of the adults will remove egg-shells from the nest after hatching;
could you simply have seen egg-shells being "cleaned" out of
the nest and dropped? Adults will also sometimes remove whole eggs that
don't hatch, fly from the nest with them and drop them (they will also
sometimes simply eat them in the nest). I have never heard of anyone witnessing
"crushing" of an egg in mid-air. Perhaps it was one of these
normal behaviors you witnessed. I have no idea what could have happened
to the fledgling. Again, after fledging, juveniles will often perch along
the shore away from the nest for a long time, in hard to observe places.
Were both adults present at the nest the whole season?
Good luck with this coming nesting season !
I'm sure your state biologists would be interested in having your observations
on this nest.
My daughter and I have had a great time watching the updates on bald eagle
migration. We have even visited the Rocky Mountain Arsenal to view wintering
eagles. As we live in Colorado, we would like information on the migration
path the eagles take in the mountain states and west coast.
Do you have access to this map? Thanks Beth and Alex
Colorado hosts a "winter" eagle population much larger than
its summer breeding population, and most of these 500-1000 birds hail
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
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.
You might also want to check out the Colorado
Division of Wildlife home page to see what they might have about eagles
(both bald and golden) in your state.
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. Not too long ago, Jim was a bald eagle contributor
to Journey North, just as I am now. I would encourage you to look back
at the archives and see if some of
his migration research is still available through Journey North: I think
you will find it very informative.
New York State Dept. Environmental
Division of Fish, Wildlife and Marine Resources