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Little skulls & cuckoos & cowbirds



Les Eastman <les_eastman@netfox.net> wrote:
>I have been biting my tongue during this "authoritative" discussion but
>feel I have to say this.  Unlike European cuckoos, North American
>cuckoos very seldom are brood parasites and in my 15 years of birding I
>have never heard of them being a problem.  Are you folks thinking of
>cowbirds?  They are a big problem and control measures have been
>instituted where they are a threat to endangered species.

Personally I just assumed everyone was talking about the common cuckoo of
Europe, the most famous avian brood parasite. The last few posts did refer
to *increasing* threats from "cuckoos" which, as you say, does sound like
a confusion of the common cuckoo with the North American Brown-headed
Cowbird, which is definitely and dangerously on the increase. 
  But back to business. A previous post asked about symbiosis. While
re-reading my Gill's Ornithology on this topic, I found one case of a
benefit from a brood parasite: nestling Giant Cowbirds pluck botfly larvae
off of the host nestlings. Botflies can kill host nestlings, and in areas
with many botflies, the host (Chestnut-headed Oropendola) tolerates
cowbirds, and the local cowbird population has conspicuous white eggs
rather than mimetic eggs. In areas with low botfly infestation, the host
rejects cowbird eggs and the cowbirds have mimetic colored eggs. Cool!

Kathleen
hunt@u.washington.edu