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From: bob@delphi.uchicago.edu (Robert S. Lewis, Jr.)
Newsgroups: rec.birds
Subject: Re: "Sparred" Owl
Message-ID: <1990Oct18.154333.3340@midway.uchicago.edu>
Date: 18 Oct 90 15:43:33 GMT
References: <1990Oct16.085100@Unify.com> <1138@sun13.scri.fsu.edu>
Sender: news@midway.uchicago.edu (News Administrator)
Reply-To: bob@delphi.UUCP (Robert S. Lewis, Jr.)
Organization: University of Chicago
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In article <1138@sun13.scri.fsu.edu> sandee@sun16.scri.fsu.edu (Daan Sandee) writes:

>As for concern : there is no evidence (apparently) of human involvement.
>So it appears to be a natural process. 


Of course, the radical changes in the nation's environment brought
about by human settlement and development may have a lot to do with
the spread of the Barred Owl.  As forests are chopped up into small
parcels, species that adapt well to the edges of forests begin to
penetrate regions which in the past were inaccessible to them.  Hence
the strategy of preserving a species by preserving small areas of its
natural habitat does not always work well.

Many birds that are spreading, are doing so because of changes in the
environment brought about by humans.  The cowbird, for instance, has
been expanding East since Europeans came to America, since it adapts well
to an environment where small woodlands are intermixed with open
areas.  This is because the cowbird is a parasitical nester that
parasitizes woodland species, but prefers to feed in open areas.
Before Europeans cleared much of the Eastern forest, cowbirds were
apparently much less common, being restricted to forest borders.  As
clearings in the forest opened up cowbirds moved in.  This was good
for cowbirds, but terrible for warblers, which used to be able to
protect themselves from cowbird paratisism by breeding deep in the
forest.  Now cowbirds can penetrate the smaller forests to the forest's
heart, leaving no safe havens for small woodland breeders.