Speaking of Wren population response, as Frank and Andy pointed out,
the USGS's North American Breeding Bird Survey (BBS) results illustrate
the population trends of this, and other species, very well.

Trend results can be viewed at the following site:
<www.mbr-pwrc.usgs.gov/cgi-bin/atlasa99.pl?07180&1&07>
The numerically inclined may wish to loiter on this page a while but
most folks will prefer to skip on to the "Maryland" link on the left
side (or proceed to the bottom and select an entire region) in order
to see the trend graph.  While a publication or two has hit on this
topic in the past, folks may find it particularly interesting to draw
their own inferences about the upcoming year by relating historical
population crashes to historical snowfall events...vs. ice events...
and/or days snow/ice coverage persisted.  Good luck and good birding!

P.s. - other species and other BBS result types (such as maps depicting
range-wide trends, etc.) can be accessed by visiting the BBS homepage
<www.pwrc.usgs.gov/bbs/> and selecting the "USGS Results and Analysis"
link.


Dave Ziolkowski Jr.
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PWRC, Laurel, MD