[texbirds] Re: Bushtits in eastern Edwards Plateau?
- From: George Baker <gn_baker@xxxxxxxxxxxxx>
- To: gcwarbler@xxxxxxxxxxxxx, TexBirds TexBirds Posting <texbirds@xxxxxxxxxxxxx>
- Date: Sun, 23 Jun 2013 20:27:08 -0700 (PDT)
I'm a bit late on this thread but wanted to add information on observations
from
our ranch in northern Kimble County - since April of 2003 when we started
keeping lists for each visit, Bushtits have been recorded on 26 of 227 trip
lists, which is about 11% of the trips. However, the vast majority of those
were recorded prior to May 2007, with Bushtits seen on only 5 trips since then
and we have had no records since January of 2011. Frequency of trips has
remained about the same, so observation effort is probably not a big factor.
As
for ebird, trip lists are entered for trips when I am there but not for those
when I'm not, so some of the data is there, but not all of it.
All that being said, I would agree that Bushtit are being encounted less often,
at least on our ranch.
Thanks,
Noreen Baker
Austin, Tx
________________________________
From: Chuck Sexton <gcwarbler@xxxxxxxxxxxxx>
To: TexBirds TexBirds Posting <texbirds@xxxxxxxxxxxxx>
Cc: Rich Kostecke <rkost73@xxxxxxxxx>
Sent: Thu, June 20, 2013 4:46:36 PM
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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