Re: [nfc-l] On the apparent complete absence of Swainson's Thrushes in the Interior West

[Jody Enck]

Ted Floyd wrote:
Ah. Colby has brought up the strange case of the missing Swainson's 
Thrushes: 


Hello everyone,
   I guess this partially answers my unasked question about whether 
Swainson's and other species migrate at some altitude not picked up by 
the equipment typically used.  But I'm still curious about the effects 
of the altitude at which a species migrates on detection rates.  How 
high can the typical software "hear?"  Related to that, what influence 
does topography have on detection.  I live in a "hollow" between hills 
that are several hundred feet higher to the north and to the south.  As 
birds migrate through my area, they need to be high enough to be over 
those hills, so how unlikely am I to detect the vast majority of birds 
migrating over my site because I am so low?


Just curious.
Jody Enck
Ithaca, NY


> Interestingly, ZERO Swainson's Thrushes were heard.  Interestingly, 
in all my nights  
> listening (a couple dozen) in Utah, I never heard a Hermit or 
Swainson's Thrush in either  
> the spring or fall.  I don't know what these birds do between the 
Cascades/Sierras and  
> the Continental Divide given my experiences thus far as I'm certainly 
quite baffled at this  
> point...

It's interesting, isn't it? In their recent monograph on the birds 
of western Colorado, Bob Righter et al. state the following for 
Swainson's Thrush: "Even during spring and fall migration, rarely 
found outside of breeding habitat, suggesting that most birds migrate 
through the mountains and mountain valleys." Coen Dexter, one of the 
coauthors of that monograph, put it even more dramatically to me 
(personal communication in front of 100+ folks when I was doing Q at 
a public talk; insert frowney-face here): There do not appear to be 
any credible records in western Colorado away from mountains and 
mountain valleys. Conversely, if you go east of the Divide, you can 
see 100+ per day on spring migration in Colorado.
 
Anecdotally, that was my impression back in my Nevada days. Swainson's 
Thrush is common as dirt in the broadleaf forests of, say, the Ruby 
Mountains (northeastern Nevada). But it was notable enough in the 
lowlands for us to put it on the hotline. And those lowland records 
tended to be from the far west (Reno area) and south (Las Vegas area). 
I wonder if they were mainly Russet-backed (Pacific slope) birds, not 
Olive-backed (everywhere else) birds.
 
Best, --Ted Floyd
 
Lafayette, Boulder County, Colorado
 
 
 
 
 
 



--


Jody W. Enck, PhD
Human Dimensions Research Unit
Department of Natural Resources
119 Fernow Hall, Cornell University
Ithaca, NY  14853  607-255-8192
www.dnr.cornell.edu/hdru/ 




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Re: [nfc-l] On the apparent complete absence of Swainson's Thrushes in the Interior West

[Brian Sullivan]

All

When I used to live on the California Channel Islands we would get hundreds
of SWTH in the pre-dawn, and then they were complete ghosts on the ground. I
mean, these things would simply disappear. It wasn't until I accidentally
found them one day that I finally realized what they were doing. Walking a
canyon bottom I flushed one out of a large cherry tree. Then a few more,
etc. Eventually there was a breaking wave of SWTH moving through the canyon
bottom ahead of me, but in the trees they were essentially undetectable. I
spent hours above on the cliffs trying to see one and never did. They must
simply stay very still and well-hidden. I don't fully understand it, I just
know that's what happens on the Channel Islands, where I heard tons and saw
very few--until I knew how to find them.

This of course doesn't mean they are in the interior west is huge numbers
too, I just thought I'd raise the visual detectability issue for this
species.

Brian

On Wed, Aug 26, 2009 at 2:21 AM, Ted Floyd  wrote:

>  Ah. Colby has brought up the strange case of the missing Swainson's
> Thrushes:
>
> > Interestingly, ZERO Swainson's Thrushes were heard.  Interestingly, in
> all my nights
> > listening (a couple dozen) in Utah, I never heard a Hermit or Swainson's
> Thrush in either
> > the spring or fall.  I don't know what these birds do between the
> Cascades/Sierras and
> > the Continental Divide given my experiences thus far as I'm certainly
> quite baffled at this
> > point...
>
>  It's interesting, isn't it? In their recent monograph on the birds
> of western Colorado, Bob Righter et al. state the following for Swainson's
> Thrush: "Even during spring and fall migration, rarely found outside of
> breeding habitat, suggesting that most birds migrate through the mountains
> and mountain valleys." Coen Dexter, one of the coauthors of that monograph,
> put it even more dramatically to me (personal communication in front of 100+
> folks when I was doing Q at a public talk; insert frowney-face
> here): There do not appear to be any credible records in western Colorado
> away from mountains and mountain valleys. Conversely, if you go east of the
> Divide, you can see 100+ per day on spring migration in Colorado.
>
> Anecdotally, that was my impression back in my Nevada days. Swainson's
> Thrush is common as dirt in the broadleaf forests of, say, the Ruby
> Mountains (northeastern Nevada). But it was notable enough in the lowlands
> for us to put it on the hotline. And those lowland records tended to be from
> the far west (Reno area) and south (Las Vegas area). I wonder if they were
> mainly Russet-backed (Pacific slope) birds, not Olive-backed (everywhere
> else) birds.
>
> Best, --Ted Floyd
>
> Lafayette, Boulder County, Colorado
>
>
>
>
>
>
>



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===
Brian L. Sullivan
Pacific Grove, CA

eBird/AKN Project Leader
www.ebird.org
www.avianknowledge.net

Photographic Editor,
Birds of North America Online
http://bna.birds.cornell.edu/BNA

Cornell Lab of Ornithology
159 Sapsucker Woods Rd.
Ithaca, NY 14850

Photographic Editor,
North American Birds
American Birding Association
www.americanbirding.org

bl...@cornell.edu
609-694-3280
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