Subject: BAld Eagle, "Once in a lifetime Experience" (fwd)
Date: Feb 19 08:17:53 2004
From: Dan Victor - dcv at drizzle.com


Dear Tweets,

I'm forwarding this for Martin as there's something askew with his email
address.

Dan Victor, Seattle, WA mailto:dcv at scn.org
Tweeters = http://www.scn.org/tweeters/

---------- Forwarded message ----------
From: "Martin Muller" <MartinMuller at msn.com>
To: "W. William Woods" <wwwbike at halcyon.com>
Cc: <tweeters at u.washington.edu>

Erin, tweets,

I have spent many (hundreds of) hours observing Bald Eagles nesting here =
in the greater Seattle area. Nothing like observing to find some answers =
(in addition to numerous more questions of course).

I love Erin's conclusion that in the case of the eagle's unsuccessful =
duck hunt "life won." That is of course assuming the eagle wasn't =
starving and will eventually die from not eating..... There's always two =
sides to every story (come to think of it, often more like three, but I =
digress).

A few thoughts on eagle hunting strategies: Bald Eagles (in this area =
and elsewhere as evident from the literature) prefer fish over birds. =
Dead over alive (less energy spent retrieving it). Yet they are expert =
hunters for live fish as well as birds. I've seen live Western Grebe =
delivered to one nest. In this particular pair that nested on a bluff =
overlooking Puget Sound the pair would often land in or near the top of =
trees at the top of the bluff, vocalizing and otherwise announcing their =
presence. The wintering flock of Western Grebes down below would =
casually drift farther offshore. More than once one of the eagles then =
would depart, leaving the other eagle perched and watchful. The grebes =
would often "relax" and float closer to shore again. We are talking =
about one or more hours of "waiting and doing nothing" here. To me it =
always appeared that the eagles were counting on the grebes not being =
able to count. I know, I'll get lots of flack for ascribing such intent =
to an animal, but you go out there and observe for a while and then come =
back and tell me that there's no intent involved in some seemingly =
purposeful animal behavior.=20

Anyway, I've only seen a few unsuccessful hunts on the Western Grebes by =
the remaining eagle. It would often single out one lone grebe and dive =
on it repeatedly, apparently hoping to try and exhaust the grebe, timing =
it so that just as the grebe popped up the eagle would be approaching. I =
never thought this would work, since grebes are expert divers and they =
will double back under water (personal experience trying to free Western =
Grebe from fishing line it was entangled in). Yet the observation at the =
nest of the adult male eagle of this same pair arriving with a (kicking =
and screaming) Western Grebe showed that in some instances the hunt can =
be successful.

An alternative strategy when dealing with water birds is for the eagle =
to swoop down and simply land on top of its prey. This works with =
American Coots as well as Mallards (seen by myself and other observers). =
Eagles float very well and can take off from the water with prey in =
their talons, provided the prey is not too heavy. Eagles can swim (in =
one instance more than 1/4 mile) dragging prey with them. Big fish or =
heavy bird (like Double-crested Cormorant). Paddling with their wings =
they can get to shore and drag the prey item onto shore with them.

It all seems to hinge on timing though. The eagle has to be coming down =
when the prey is coming to or is at the surface. So rather than =
interpreting Erin's observation as attempts to flush the ducks into =
flight, I think the eagle was trying to time its arrival with the =
surfacing of one of the ducks diving for safety. Eagles don't as a rule =
hunt prey on the wing. That's more falcon behavior.

Having said that I have to admit that I observed one adult female eagle =
"thermaling" up one time, watching her through my binoculars, =
appreciating the little twitches in the primaries and tail to fall =
steadily up. Suddenly she tucked her wings and came diving straight =
down, like a falcon in a full stoop. Momentarily I got a little worried, =
since she was heading straight for me, or so I thought. Just as I was =
convinced this bird was very confused a male Mallard zipped through my =
binocular's field of view. A little twist, a zigzag by the duck and the =
eagle missed, pulling up sharply to avoid colliding with the treetops =
next to me. It was the first time I saw an eagle behave like a falcon, =
seriously trying to slay a duck on the wing. But like a falcon it needed =
to gain speed/momentum by stooping from great height. Quite a different =
scenario than an eagle maneuvering in tight quarters and at relatively =
low speed over a pond, as described by Erin.

Yet, there is that old mantra: "never say never." I just hope the eagle =
will return to Erin's pond and prove me wrong. It would be ever so neat =
to observe!

Okay. Time to go outside and go observe some bird behavior. I talked =
myself into it.

Cheers,
Martin Muller
Olympic Manor, Seattle, WA
martinmuller at msn.com