Last Saturday, my wife, her mom, our three-week old daughter
and I went up to the Skagit Flats to look for Snow Geese,
Trumpeter Swans and other attractions of the flats. We found
a flock of Snow Geese near the "middle access" on Fir Island,
on one of the fields owned by the Skagit Gun Club. Not long
after we arrived, a pair of Bald Eagles took a run at the Snow
Geese and the whole flock took flight in that wonderful spectacle
that they are know for. The geese flew over to the delta, so we
went up on the public access to the dike and watched some more
from there. About half-an-hour to an hour later, the Eagles took
another run at the geese, and the spectacle was repeated, with
the geese returning to the field.

While we were up on the dike, a tour group from the Seattle
Aquarium showed up. There was a guide with the group whose
name I did not catch (If you are out there, my apologies),
but I am sure is probably a well-know expert around here. While
addressing the group he commented that the Snow Geese were
probably not really in much danger from the Eagles, but they
were just playing it safe.

I have been thinking about that comment and about the whole
Eagle/Snow Goose spectacle and wondering if that is true.
It seems odd to me that the geese would expend as much energy
as they do to avoid a predator that doesn't really pose much of
a threat. In the hour or so that we watched them they were
stirred up at least three times. That seems like a significant
disruption of their feeding time. If the Eagles really don't
pose a threat, I would think they would figure it out after
a little while.

On the other hand, a snow goose is a big bird for a Bald Eagle
to tackle, and while I have seen several Eagles do their
"strafing runs" on flocks of Snow Geese, I've never seen
them actually get one.

The Bald Eagles we observed on Saturday definitely seemed
to be following some sort of hunting strategy. They would
fly at the flock of geese in pairs, one flying high over
the flock, which stirred them up, the other flying low, as if
looking for a lagger. There was also a sub-adult Bald Eagle
in the area that repeatedly flew near the flock, but never
stirred them up, while this pair seemed to deliberately target
the flock.

I guess I see four possibilities here.

1)Eagles do hunt Snow Geese, occasionally taking a sick
or injured bird, and the hunting pattern I saw on Saturday
was their stratagy for stirring up the flock to find one that
was sick or injured.

2)Adult and juvenile wintering Snow Geese are really too
big for the eagles to get, but up in their northern breeding
grounds Bald Eagles raid the nests and get chicks. The
winter behavior is a residual result of their behavior on
the nesting grounds.

3)Eagles really don't pose a threat, but none of the Snow Geese
want to be the one to prove it, and the eagles are either
ambitious or they're just having fun making all the geese go ape
(this was the explanation the aquarium guide seemed to prefer).

4)The eagles don't pose a threat but there is some other adaptive
reason for the behavior. (Maybe the geese need the exercise? The
eagles could be their personal trainers?)

What do people think? Has anyone seen an eagle take a Snow
Goose? Has there been some research done on this?

Thanks for the thoughts, in advance.

John Chapman
Seattle, Washington
Email to: ragweed at igc.org