[texbirds] Bushtits in eastern Edwards Plateau?
- From: "Collins, Fred (Commissioner Pct. 3)" <Fred_Collins@xxxxxxxx>
- To: "'gcwarbler@xxxxxxxxxxxxx'" <gcwarbler@xxxxxxxxxxxxx>, "TexBirds TexBirds Posting" <texbirds@xxxxxxxxxxxxx>
- Date: Fri, 21 Jun 2013 14:10:25 +0000
Great use of E-bird data Chuck. It would certainly appear that Bushtits are
down substantially.
But more importantly where can I buy that $0.25 cup of coffee?
Fred Collins
(281) 357-5324
Director: Kleb Woods Nature Center
Cypress Top Historical Park
Commissioner Steve Radack
Harris County Precinct 3
www.pct3.hctx.net
-----Original Message-----
From: texbirds-bounce@xxxxxxxxxxxxx [mailto:texbirds-bounce@xxxxxxxxxxxxx] On
Behalf Of Chuck Sexton
Sent: Thursday, June 20, 2013 4:46 PM
To: TexBirds TexBirds Posting
Cc: Rich Kostecke
Subject: [texbirds] Re: Bushtits in eastern Edwards Plateau?
Rich and TexBirders--
Thanks for the very thoughtful reply about Bushtits. I know I oversimplified
some of the questions about Bushtits in my TexBirds posts. I put it out there
to get people thinking about trends, species comparisons, etc. I think your
details are spot on regarding Bushtit vs Hutton's Vireo. IMHO, eBird has
substantial biases that will always need to be kept in mind, particularly with
respect to consistency of coverage, observer (target) biases, levels of effort,
etc. That said, as was said of CBCs many decades ago, en masse they might be
taken as an overview of gross trends in abundance and distribution, with
caveats.
I did a very quick gross analysis of Bushtit eBird data for ALL OF TEXAS as
follows:
-- I looked at three unequal reporting periods: (1) recent drought years
2010-2013; (2) the "pre-drought" decade (...I know, I know...), 2000-2009; and
(3) all previous "historical" data uploaded to eBird (1900-1999).
-- I looked at only breeding season (June-July) reports.
-- Since sample sizes* are widely different and the flocking behavior of
Bushtits gives rised to highly variant individual counts, I only looked at
"Frequency" of occurrence on submitted checklists. (* For instance, the weekly
sample size of Texas checklists for June-July available in my three periods
averages about 300 for the historical checklists, about 1700 for the
pre-drought decade, and 2500 for the recent drought period.)
Results: In June and July, for the historical period of record, Bushtits were
reported on anywhere from 0.55 - 2.2% of all submitted checklists weekly in
Texas. For the pre-drought decade, with the considerably larger sample size,
Bushtits show up weekly on 0.76 to 2.8% of checklists, not a particularly vivid
difference. And for the recent drought years, with the largest sample size,
they show up on only 0.33 to 0.62% of checklists, an obvious drop in frequency
on submitted checklists.
I've done no statistics on this, nor any further geographical breakdown....and
probably won't....but what this *suggests* is that despite the increased
observer coverage and reporting to eBird in recent years, Bushtits are
definitely being encountered less often from observers who are afield.
This analysis and $0.25 will get you a cup of coffee; I am not expecting a
Nobel Prize for it. But it does support my general impression...with data.
Now I'll have to leave it up to some bright Cornell undergraduate to delve into
eBird data with more temporal and geographic grace and charm to tell us what is
really happening!!
Thanks again for your thoughts.
Chuck
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