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Estimating the Abundance of Eared Grebes on Mono Lake, California, by Aerial Photography

W. Sean Boyd and Joseph R. Jehl, Jr.
Colonial Waterbirds
Vol. 21, No. 2 (1998), pp. 236-241
Published by: Waterbird Society
DOI: 10.2307/1521912
Stable URL: http://www.jstor.org/stable/1521912
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Estimating the Abundance of Eared Grebes on Mono Lake, California, by Aerial Photography
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Abstract

We used an aerial photography protocol to estimate the number of Eared Grebes (Podiceps nigricollis) staging on Mono Lake in the fall of 1996 and 1997. Three analytical techniques, a non-stratified and two stratified ones, generated similar abundance values for any given date. The stratified by-quartiles method resulted in the lowest percent SEs but this method and the non-stratified one are sensitive to the quantity and quality of photo coverage. The stratified-by-density method was more time/effort consuming and resulted in intermediate percent SEs but is more robust than the other methods. Total abundance differed by < 3% across consecutive days in October, 1997, which suggests that the photo protocol is reliable. Our data indicate that a minimum of 1.5 to 1.6 million grebes were present on the lake in October of each year. When these estimates are corrected for submerged birds, they increase to 1.8 to 2.0 million birds, confirming that Mono Lake is the most important fall staging site for Eared Grebes in North America.

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