wrote:

>Recent emails about Song Sparrows and others feeding young Cowbirds got me thinking and wondering about something....
>I assume that hosting parents of Cuckoos feed them what they instinctively feed their own young.  I can't imagine a seed-eating parent fulfilling the nutritional needs of Cuckoo nestlings when adults (I understand) feed almost exclusively on insect fare, primarily caterpillars.  Do adult Cuckoos, or Cowbirds for that matter, seek the nests of species that feed their young the proper diet?
>To the extent that fledged Cuckoos learn gleaning techniques from observing their parents, how is it that they successfully feed themselves as adults without that example?
>I'm sure I'm not the first to wonder about this.  Answers, anyone?
>
>  
>
Bent's _Life Histories of North American Birds_ series quotes a 1900 
study indicating that the Cowbird diet is 77% vegetable (mostly seeds) 
and 23% animals (largely/mostly insects).  Although this is presumably 
the adult diet, it indicates that Cowbird young should be able to handle 
a diet of seeds if that is what they get.  He also makes, in the context 
of feeding amount and duration, the obvious comment that natural 
selection would select against Cowbirds using hosts that did or could 
not feed the young properly.

Bent of course has nothing to say about nest-parasitic Cuckoos since 
they are not North American.

-- 
Maurice Barnhill 
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Department of Physics and Astronomy
University of Delaware
Newark, DE 19716