Konter • INTERBREEDING OF AECHMOPHORUS GREBES 
719 
Hybridization in the case of Aechmophorus grebes 
seems to be progressing while in the Held its 
real extent might be masked by the effects of 
inlrogression. Mate choice may be less apparent 
when the population consists almost entirely of 
highly recombined hybrids (Barton and Hewitt 
1985). Feerer (1977) found intermediates to be 
extremely frequent representing 30 and 51% at two 
lagoons in surveys of Mexican Aechmophorus 
populations, generally dominated by Clark's Grebes. 
Repetition of this study for Mexican populations, 
coupled with genetic analyses, is needed in reviews 
of the taxonomic status of Aechmophorus grebes. 
ACKNOWLEDGMENTS 
I thank my wife Maria for assistance during fieldwork in 
Utah, and the referees and the editor of the Wilson Journal 
of Ornithology for their welcome and useful comments on a 
first draft. 
LITERATURE CITED 
Ahlquist, J. E.. a. H. Bledsoe. J. T. Ratti, and C. G. 
Sibley. 1987. Divergence of the single copy DNA 
sequences of the Western Grebe (Aechmophorus 
occidentalis ) and Clark's Grebe (A. clarkii). us indicated 
by D.NA-DNA hybridization. Postilla 200:1-7. 
American Ornithologists’ Union (AOU). 1985. Thirty- 
fifth supplement to the American Ornithologists' Union 
check-list of North American birds. Auk 102:680 6X6. 
Andersen. E. and L. HUBRK’IIT. 1938. Hybridization in 
Tradescantia. III. The evidence for introgressive 
hybridization. American Journal of Botany 25:396-402. 
Baker, M. C. and J. T. Boyi.an. 1999. Singing behavior, 
mating association and reproductive success in a 
population of hybridizing Lazuli and Indigo huntings. 
Condor 101:493-504. 
Barton. N. II. AND G. M. Hewiti. 1985. Analysts of 
hybrid zones. Annual Review of Ecology and 
Systematics 16:113-148. 
Bell. D. A. 1997. Hybridization and reproductive perfor¬ 
mance in gulls of the Imius .t? Uiiicescens-occulenialis 
complex. Condor 99:585-594. 
Bledsoe, a. H. and F. IT Sheldon. 1989. The metric 
properties of DNA-DNA hybridization dissimilarity 
measures. Systematic Zoology 38:93-105. 
Eichhorst. B. a. and B. D. Parkin, 1991. Clark s Grebes 
and suspected Western X Clark's grebe hybrids in 
Manitoba. Blue Jay 49:196-200, 
Feerer, J. L. 1977. Niche partitioning by Western Grebe 
polymorphs. Thesis. Humboldt State University. 
Areata, California. USA. 
Guerra. R. andT. P Speed. 1996. Statistical issues arising 
in the analysis of DNA-DNA hybridization data. 
Systematic Biology 45:586-595. 
Hebert. P. D. n., S. Ratnasingiiam. and J. R. df. Ward. 
2003. Barcoding animal life: cytochrome c oxidase 
subunit I divergences among closely related species. 
Proceedings of the Royal Society of London. Series B 
270:313-321. 
Hoffmann, w„ j. A. Wilns. and J. M. Scott. 1978. 
Hybridization between gulls [Units glaucescens and L. 
occidentalis ) in the Pacific Northwest. Auk 95:441— 
458. 
Howard. D. J., S. C. Bkitch, W. E. Braswell, and J. L. 
Makshai i. 2003. Evolution in hybrid zones. Pages 
297-314 in The evolution of population biology (R. K. 
Singh and M. K. Uycnoyama. Editors). Cambridge 
University Press. Cambridge. United Kingdom. 
Kerr. K C. R.. M. Y. Stueckle. C'. J. Dove, L. A. Weigt, 
C'. M. Francis, and P. D. n. Hebert. 2007. 
Comprehensive DNA barcode coverage of North 
American birds. Molecular Ecology Notes: doi: 
10.1111 /j. 1471-8286.2006.01670.x. 
KONTER. A. 2009. Occurrence of Clark's Grebes and their 
hybrids with Western Grebes in Prairie Canada. Blue 
Jay 67:26-33. 
Konter. A. 2011. Interbreeding of Aechmophorus grebes. 
Wilson Journal of Ornithology 123:132-136. 
Lindvai L. M. E. AND .1. B. LOW. 1982. Nesting ecology and 
production of Western Grebes at Bear River Migratory 
Bird Refuge. Utah. Condor 84:66-70. 
MrlVOR. D. E. 1998. Birding Utah. Falcon Publishing, 
Helena, Montana. USA. 
NUECHTERLEIN, G. L. 1981a. Courtship behavior and 
reproductive isolation between W'estem Grebe color 
morphs- Auk 98:335-349. 
NUECHTERLEIN, G- L. 1981b. Variation and multiple 
functions of the advertising display of Western Grebes. 
Behaviour 76:289-3)7. 
NUECHTERLEIN. G. L. AND D. P. BuiTRON. 1998. Interspe¬ 
cific mate choice by late-courting male Western 
Grebes. Behavioral Ecology 9:313-321. 
Nuechtkrlkin. G. L. and R. W. Storer. 1982. The pair- 
formation displays of the Western Grebe. Condor 
84:351-369. 
Price, T. D. and M. M. Bouvter. 2002. The evolution of 
FI post/ygolic incompatibilities in birds. Evolution 
56:2083-2089. 
Ranollk, C. 2004. Frequency of bird hybrids: does 
detectability make all the difference? Journal of 
Ornithology 145:123-128. 
Randi er. C. 2006, Behavioural and ecological correlates 
of natural hybridization in birds. Ibis 148:459-467. 
Randlek. C. 2008. Mating patterns in avian hybrid zones-a 
meta-analysis and review. Ardea 96:73-80. 
Rasmussen, P. C. 1991, Relationships between coastal 
South American King and Blue-cved shags. Condor 
93:825-839. 
Ratnasingham, S. and P. D. N. Hebert, 2007. BOLD: 
The barcode of life data system. Molecular Ecology 
Notes 7:355-364. 
Ratti, J. T. 1979. Reproductive separation and isolating 
mechanisms between sympatric dark- and light-phase 
Western Grebes. Auk 96:573-586. 
Ratti. J. T. 1981. Identification and distribution of Clark’s 
Grebe. Western Birds 12:41-46 
Savolainen, V., R, s. Cowan, A. P. Vogler, G. K. 
Roderick, and R. Lane. 2005. Towards writing the 
