Subject: Re: Eagles and Heron Nesting Disturbance?
Date: Jun 4 15:56:41 1996
From: Dennis Paulson - dpaulson at mirrors.ups.edu


Don Baccus wrote:

>Since bald eagles are highly territorial during the breeding
>season, only one pair is likely to ever include a particular heronry
>in their territory. So, the effect is likely going to depend on
>the size of the heronry.

I dunno. My guess is that one eagle with moderate ease can cause desertion
of a heronry of almost any size (although see below). I suppose there
might well be variation among eagles in their interest and persistence in
such matters.

>I wonder if herons ever mob a maurading eagle? That would be a sight
>to see!

It would indeed. Rick Droker told me that when he saw a Bald Eagle eating
the eggs in a heron nest at Nisqually, the heron advanced on the eagle and
actually struck at it (from a respectful distance), but the eagle ignored
it. Apparently the other herons in the colony remained at their nests
while this particular interaction took place. The observers left without
knowing whether the event was repeated at another nest, but one could
imagine an eagle returning again and again with impunity until each heron
clutch was eliminated. I don't know how many such visits it would take for
the entire heronry to desert.

I know nothing about the effects of eagles on storkeries, ibisries, and
spoonbilleries.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416