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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 4. December 2012 
TABLE 1. Characteristics of Aechmophorus grebe study sites in Utah. USA. 
Geographical coordinates 
Name 
Water surface (ha) 
Elevation (m asl) 
N 
E 
Farmington Bay 
7,300 
1.280 
40 56.841 
111 56.151 
Ogden Bay 
8,000 
1.280 
41°11.198 
112 09.667 
Willard Bay 
1.280 
41 25.259 
112 03.454 
Mantua Reservoir 
1.585 
41 29.837 
111 55.920 
Yuba Lake 
2,(MX) 
1.520 
39 ’22.400 
112 01.382 
Minersville Reservoir 
450 
1.685 
38 13.680 
112 48.893 
Panguitch Lake 
1.600 
2,510 
37°43.343 
112°38.046 
Lake Powell 
1.100 
37 53.293 
110 24.049 
Bottle Hollow Reservoir 
160 
1.560 
40 17.674 
109 53.085 
Strawberry Lake 
7.900 
2,315 
40 10.497 
11 TO 1.694 
Benson Marina 
3.340 
41 47.21 I 
111 57.245 
Cache Junction 
1,350 
4 f 50.692 
112 00.145 
Hyrum Reservoir 
750 
1,420 
41 ”37.602 
111 52.315 
Jensen Park pond 
1,295 
41 03.967 
112°03.266 
Pelican Lake 
7(H) 
1.470 
40 1 12.002 
109 41.519 
Ouray NWR 
500 
1.420 
40 07.248 
109 38.519 
Bullock Reservoir 
1.610 
40 21.144 
109 49.115 
Cottonwood Reservoir 
1,600 
40 21.135 
109 47.135 
Deer Creek Reservoir 
1,300 
1.650 
40 28.424 
11 1 28.409 
Syracuse; Pelican Lake; Wyasket Lake and pond 
on Ouray National Wildlife Refuge, Bullock 
Reservoir, Cottonwood Reservoir, all close to 
Roosevelt; and Deer Creek Reservoir in the Heber 
Valley near Heber. The results from these wetlands 
were aggregated under other sites visited. Public- 
access to Bear River Migratory Bird Refuge that 
has an important Aechmophorus population was 
closed due to road construction and a request for 
exceptional access did not receive a positive reply. 
Water surfaces, elevations, and geographical 
coordinates of study sites varied (Table 1). 
Timing and Recording of Data.— Study sites 
were visited between 8 and 25 July 2010. I 
stopped to identify grebes any time they were 
encountered. Nesting grebes were only present at 
Farmington Bay, Crystal Unit. No attempt to 
completely assess pair composition was under¬ 
taken to minimize disturbance to this mixed 
colony of Western, Clark's, Eared ( Podiceps 
nigricollis), and Pied-billed grebes (Podilvmbus 
podiceps). Aechmophorus families were encoun¬ 
tered at Panguitch Lake, Bottle Hollow Reservoir 
Ouray National Wildlife Refuge, and Strawberry 
Lake. 
Total numbers of Aechmophorus grebes present 
were counted at each site using Zeiss 10 x 25 
binoculars or, in a few cases, their numbers were 
estimated. All grebes sufficiently close for species 
identification were scanned using a Konica 
Minolta Dynax 7D camera and a Sigma AF 
800 mm auto focus lens mounted on a tripod. 
Species (Western, Clark’s or intermediate) was 
recorded after identification by an assistant. Up 
to three photographs were immediately laken 
lor each grebe not entirely conforming to the 
descriptions of Storer and Nuechlerlein (1985) for 
Western or Clark’s grebes. Photographs were 
visualized later using Program Photoimpact that 
allows sufficient magnification with negligible 
loss of quality. Species composition of pairs 
encountered was also recorded. 
Identification of Grebe Species (Western vs. 
Clark's). —Species identification of exclusively 
adults followed the descriptions provided by 
Storer and Nuechterlein (19S5). They subdivided 
diverging areas of the plumage of the face 
between Western and Clark’s grebes into lores, 
above eye. behind eye and below eye (Storer and 
Nuechterlein 1985:103; figure I). Their criteria 
were complemented by review's in Ratti (1981), 
Eichorst anil Parkin (1991). and Konter (2009). 
Individuals were classified as Clark's Grebes if 
they had while lores and w'hite feathers above, 
behind, and below the eye so the black crown 
ended clearly above the eye. and an orange- 
yellow hill with a sharply defined black culmen. 
Individuals were classified as Western Grebes if 
they had a dull yellow-green bill and the black of 
the crown extended to well below the eyes. Bills 
