Blake and Tweeters,

As I said in my earlier posting, I am sure that Bald Eagles AS A
SPECIES are mainly fish-eaters, and eaters of dead fish at that.
However, you are mistaken if you believe that capturing and eating
birds is only an infrequent, occasional aberration in Bald Eagle
behavior. There are entire populations of Bald Eagles-- small
populations, at least-- which subsist mainly on waterfowl for months
at a time, even if they turn to mainly eating fish in the summer.
In my post earlier today, I referred to Bald Eagles hunting coots
on Nicola Lake, B.C. These eagles are part of a small wintering
population in the Nicola Valley which probably lives mainly on ducks
at least from December through March. As part of the B.C. Interior
swan and eagle count organized by Rick Howie on January 16th, I
counted 24 Bald Eagles in the Nicola Valley. Sixteen of these were in
a 3-km stretch of the Nicola River just below Nicola Lake. There is a
large cattle feedlot next to the river here which provides wintering
habitat for up to 2500 or 3000 Mallards in December (although these
numbers may have dropped somewhat by February). As you mentioned, when
Bald Eagles do hunt birds, they undoubtedly concentrate on sick or
injured birds, which are easier to catch. With 2500 Mallards, there
are bound to be a number of sick or injured birds at any given time,
and there is considerably mortality over the winter. (Not that Bald
Eagles are not capable of catching perfectly healthy Mallards-- they
are!).
I don't have proof that the Mallards are the mainstay of the
eagles' diet, but there is no other explanation for them concentrating
in this area. Fish are not readily available most winters. Coho
salmon, the latest species of salmon to spawn in the Nicola Valley,
are usually finished spawning by late November. Furthermore, even in
winters when Nicola Lake is completely frozen (not so far this
winter), along with most of the Nicola River, quite a few eagles are
present. We tallied 20 eagles in the valley one January when all the
lakes were completely frozen over, along with most of the mileage of
the Nicola River. Few fish would have been available; for the most
part, it's Mallards for supper, or nothing.
Interestingly, I have observed on a number of occasions that Bald
Eagles concentrate around cattle calving areas in late February and
March in the B.C. southern interior. The attraction here is mainly the
afterbirth, which provides an abundant food source for a short time--
much more than the few calves which are stillborn or die in their
first couple of days. And, despite some opinions to the contrary, Bald
Eagles very rarely kill live newborn ungulates-- in contrast to Golden
Eagles, which do so regularly in many areas.
A group of 20 or 24 Bald Eagles may not seem like a large
population that is dependent on waterfowl for food. However, I
strongly suspect that the 600 or so Bald Eagles that winter in the
Klamath Basin of Oregon and California are mainly eating waterfowl
too, and that there are not too many fish available. If someone has
any information, pro or con, on this, please respond!
So in summary, even if Bald Eagle ecology is largely centered
around fish and fish-eating, I think there is abundant evidence that
sizeable chunks of the eagle population are mainly dependent on birds,
and especially waterfowl, as food for part of every year. Hunting
waterbirds is not an aberration or unusual occurrence; it is regular,
normal part of the lifestyle of Bald Eagles.

Wayne Weber
Kamloops, B.C.
wayne_weber at nc.sympatico.ca


-----Original Message-----
From: Blake Iverson <bswallow25 at hotmail.com>
To: tweeters at u.washington.edu <tweeters at u.washington.edu>
Date: Tuesday, January 25, 2000 7:02 PM
Subject: Eagles and their avian prey


>
>
> Well, I have been reading all of these messages on eagles and their
avian
>prey. I am sure all these have happened over a course of time....
(meaning,
>one person sees the attack on a bird, then a few hours later or a few
days,
>weeks and or months later. Not one after the other like avian prey
was all
>they eat) Golden Eagles seem the ones to be the birds to take the BIG
ones
>like geese and stuff
>(RARELY!). This odd event most likely occurs when there is a shortage
a prey
>(Fish) or taking the upper-hand and attacking injured or sick birds.
Even
>though we have plenty of fish, Bald Eagles still remain mostly a fish
eater.
>Up in Alaska, they may not witness all of these wonderful sights like
we do
>(more wilderness to hunt fish). If they have had many successes in
hunting
>avian prey during their life, then they sure will try it again. Its
just
>like the African Fish Eagles of Africa. They eat mostly fish, but
some will
>establish hunting territory near a lake where thousands of flamingos
roost,
>nest and feed. Doesn't mean they are like an accipiter. Well I have
said my
>part, fill free to correct me on anything, keep on birdin'!!
>
>-Blake
>Stanwood, WA
>bswallow25 at hotmail.com
>______________________________________________________
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>