Subject: Cowbird Predation and patchwork environments
Date: Jan 13 16:23:11 1999
From: Kai Schraml - thekaiser at earthlink.net


I would add to the thoughts below that often human disturbance in a previously undisturbed area becomes the "launching pad" for intrusive species. Cowbirds are perhaps the clearest example of this. Many forest species of perching birds are becoming increasing victims to cowbirds because they take advantage of "corridors" we as humans have provided through roads, farms, etc... Previously large miles of solid forest, or desert, or mountain areas were effective barriers to the parasites spread. However, much like migrating waterfowl require appropriate habitat to effectively "leap frog" their way between destinations, so to, cowbirds and other "undesirables," successfully leap through our human made corridors. These areas of habitat would otherwise be impenetrable to them. Thus they are able to pressure previously secure populations of "desirable" species. The declines of the Bell's vireo on the west coast is a prime example of this phenomena.

My two cents,

Kai Schraml

thekaiser at targetearth.org



Date: Tue, 12 Jan 1999 00:50:50 -0800 (PST)
From: "Jack Bowling" <jbowling at direct.ca>
To: "tweeters at u.washington.edu" <tweeters at u.washington.edu>


Re: The primary cause of declining native species?
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Michele wrote:

<snip>
>House Sparrows and Starlings etc. are highly adaptive and seem to thrive
>where human activity provides easy food and nesting "habitat." So it seems
>to me that human encroachment into wildlife habitat and the resulting
>habitat loss/degradation are among the primary factors that cause declines
>in native species.

In almost all cases, what is bad for one species is good for another. When
humans move in, the loss of habitat is bad for native warblers, sparrows, etc.,
but good for robins, House Sparrows, crows, and starlings. And yes, humans
create their own habitat, a feat matched by the busy beaver.

>I'm interested to learn more. Does anyone have any information and/or
>examples of where introduced Sparrows and Starlings cause problems in our
>remaining WILD areas where human activity is not in close proximity? I
>would presume that most farmland wouldn't be included as a wild area as it
>is often modified from a pre-existing natural state, or at the very least,
>disturbed.

No doubt there is evidence somewhere. I am willing to bet that problems are
more rampant in southern latitudes, though. At the northern edge of their range
in Canada, both starlings and House Sparrows are so tied to human habitation
that their zone of influence on surrounding birds is negligible.


---------------------------
Jack Bowling
Prince George, BC
jbowling at direct.ca