[Tweeters] Pewees and Cowbirds

rccarl at pacbell.net rccarl at pacbell.net
Wed Aug 18 04:00:23 PDT 2010


We went to a lecture in Tucson on the genetics of behavior that demonstrated how many species have adapted to avoid incubating cowbird or cuckoo eggs, but all species will feed a young cowbird or cuckoo.  In evolutionary terms, not much is lost if you accidentally toss your own egg in the process of avoiding cowbird eggs, but the loss of not feeding a hatched chick is too much to risk. 

It's well known that cowbirds will travel a long way from feeding to nest sties but they avoid deep forest. See Rothstein,S .L., Verner, J., and Stevens,E . 1984. Radio-tracking confirms a unique diurnal pattern of spatial occurrence in the parasitic Brown-headed Cowbird. Ecology 65:77 -88.

Since Western Wood-Pewees are deep forest nesters, they are rarely parasitized,  In the High Sierra, where cowbirds didn't arrive until the late 1960's and host species have not adapted, I've witnessed the collapse of such ground nesting species as Nashville Warblers.  We don't have grazing near Tahoe anymore but pack-stations and recreational stables provide more than enough feeding to maintain a thriving cowbird population. 

Richard Carlson

Full-time Birder, Biker and Rotarian

Part-time Economist

Tucson, AZ, Lake Tahoe, CA, & Kirkland, WA

rccarl at pacbell.net

Tucson 520-760-4935

Tahoe 530-581-0624

Kirkland 425-828-3819

Cell 650-280-2965

--- On Tue, 8/17/10, Scott Ramos <lsr at ramoslink.info> wrote:

From: Scott Ramos <lsr at ramoslink.info>
Subject: [Tweeters] Pewees and Cowbirds
To: "Tweeters" <tweeters at u.washington.edu>
Date: Tuesday, August 17, 2010, 10:02 PM

Tweets,

Just returned from a long weekend camping trip in central Oregon. Nothing too remarkable in the limited time I was able to escape from the group to bird, except I observed a pair of Western Wood-Pewees feeding a juvenile Brown-headed Cowbird. From a limited search on the internet (e.g., Nesting Success of the Western Wood-Pewee in Colorado, Western Birds, 28:110-112, 1997), it seems that only some tyrannid flycatchers are parasitized by cowbirds while others, including the pewees, are much less so. So, I was wondering if others have made similar observations.

Scott Ramos
Seattle
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