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October 2005 Eared Grebe numbers

From: Greg Reis on behalf of Sean Boyd
Date: 10 Jan 2006
Time: 13:35:30 -0500
Remote Name:


Here are the results of the EAGR photo count conducted on Mono Lake in mid-October 2005:
Total = 936,617
%SE = 4.7%
N = 655 photos

This is a fairly large increase over the previous year, mid-October 2004:
Total = 665,335
%SE = 6.8%
N = 310 photos

Ron VanBenthuysen of Cal DFG conducted the photo count and he more than doubled the number of photos taken over last year. Although not really needed this year because the birds were fairly evenly distributed, the larger sample size will help reduce the variance in years when grebes are highly clumped. For this data set, I generated total estimates using every 2nd, 3rd, and 4th photos and found that, while the totals varied by up to 50,000 birds over the baseline number above, the %SE increased to ca. 7%, 8.5% and 10%, respectively.

Also, using Ronís PhotoLink setup I was able to correct density values for altitude variability, and this made a difference of about 70,000 birds over the uncorrected total.

I think the protocol we now have established for Mono Lake is a good one. Thanks to Ron, Esther, Melanie, Dan and others at Cal DFG for making the arrangements and conducting the survey. Also thanks to Greg Reis for supplying data to calculate the surface area of Mono Lake. Please forward this to others who may be interested.


More on 2004 and previous years:

This count is quite a bit lower than most of the mid-October counts I did in the 1990s, as follows:

1996: 1.5 million
1997: 1.6 million
1998: 0.8 million (post el nino year)
1999: 1.1 million
2000: 1.6 million
2001: 1.2 million
2002: no count
2003: no count
(All the above counts can be increased by 15-20% to account for submerged birds.)

Digital photos were used for the first time this year by Cal DFG which is definitely the way to go. We are in the process of developing an even better protocol for next year to improve coverage and reduce variance. Thanks to Ron VanBenthuysen, Dan Yparraguire, and Melanie Weaver of Cal DFG for setting up and conducting the aerial survey and Peter Vorster, Gregory Reis and Geoff McQuilkin for supplying info on how to calculate lake surface area.

Last Updated August 09, 2007

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