[CT Birds] chickadees and titmice
Steve Mayo and Rebecca Horowitz
rsdmayo at sbcglobal.net
Tue Dec 17 21:50:52 EST 2013
Thanks Chris, for this very informative post and links.
From: Chris Elphick <elphick at sbcglobal.net>
To: CTbirds <ctbirds at lists.ctbirding.org>
Sent: Tuesday, December 17, 2013 7:33 PM
Subject: [CT Birds] chickadees and titmice
Short term fluctuations in bird populations are very normal, and are likely to be especially common in species that are relatively short-lived and produce a lot of young per clutch (e.g., chickadees and other parids). This is why systematic surveys conducted with a well-defined protocol over multiple years are essential for assessing bird population changes. By far the best source of data for such analyses is the USGS Breeding Bird Survey (BBS) - although this survey is not perfect it is much better than anything else we have. A couple of years ago Chris Field did a thorough analysis of BBS data for >100 species for which there was adequate information from CT. His analysis accounts for variation in observer effort and a number of other issues that plague analysis of this type of data.
The results are all posted on the ctbirdtrends.org web site:
At this site you can create custom-made graphs for species of your choice, or you can look at the pre-made figures we put together for groups that we though people would be especially interested in. If you'd like to see how trends in all analyzed species compare, go here:
It just so happens that chickadees and titmouse (plus white-breasted nuthatch) are in one of the pre-made graphs. Over the 40+ year period of the analysis (1966-2009), chickadees showed a steady increase in numbers (overall increase averages ~2-3%/yr), but with a lot of short term ups and downs. Titmice increased more rapidly (average increase of ~6%/yr), with even more fluctuations. You can view the parid figure here (note that I had trouble viewing it in firefox, but not in chrome ... not sure why, but my posting about it will no doubt send Chris off to the source code to figure it out!):
Of course, these analyses all refer to breeding populations. Chickadees are also migrants, so winter impressions may be further complicated by how many birds move south in a given year, and how many of those that move stay in southern New England rather than going farther.
elphick at sbcglobal.net
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