Terry Wahl, who is a rancher on the southern Oregon coast, recently described
to me the predator avoidance strategy of Yellow-rumped Warblers and Western
Bluebirds (and smaller numbers of Palm Warblers) that they use to avoid falcons
and accipters. I apologize if I mis-state any aspects of his observations.
Terry is a remarkable observer of the habits of birds on the ranch.
I recently birded with Terry on his family's ranch. There were about 100
Western Bluebirds and large numbers of Yellow-rumped Warblers (and there are
as many as 20 Palm Warblers on the ranch). All three species associate in
multi-species flocks. Generally, these species feed near the many fences on
the ranch, Many of the fences are hatched in squares that are fairly small -
maybe 4 just four inches between lines - but maybe a bit longer distances
between joints). While all species will go into the center of fields, most of
their time is spent near the fence lines, which are numerous. When they feed
some distance from the fence lines their feeding is usually short in duration.
Terry remarked that the flocks of these species, which are often quite large,
habitually go from the side of the fences from which the raptors attack to the
protected side. The small prey species easily go through the fences. The
raptors generally can't go through the fences, or do so only with difficulty
and not with speed. When a raptor goes over the fence in pursuit of the
potential prey species, the prey species just go back through the fence to the
side where the chase started. In this way, the potential prey species are able
to feed the rich open habitat that is enhanced by management that mimics the
feeding habits of bison in pre-Columbian times (and therefore does not
generally require tillage, pesticides, or fertilizers) and feed in open areas
generally without trees or bushes.
Jeff Gilligan
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