Aechmophorus occidentalis/A. clarkii

Western and Clark’s grebes were once considered color morphs of a single species. In 1985 the American Ornithologists’ Union (1998) decided these two were separate, based on DNA-DNA hybridization data, bill color, facial plumage, vocalization and courtship behavior differences.

These two species may be best known for their elaborate courtship displays, possibly the most conspicuous of any bird species. The displays of the two species differ only in the number (one or two) of notes in their Advertising calls. These calls, plus bill color and facial pattern differences, allowed researchers in recent years to determine the two species mated preferentially with conspecifics (Storer and Nuechterlein. 1992a, b).

DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, atlasers found confirmed breeding in latilong-quad 30103-H6; perhaps the mixed pair described by Lockwood and Freeman (2004) on Balmorhea Lake in 1991 as the first breeding record for Texas. These authors also describe nesting evidence for an additional mixed pair as well as breeding by Western Grebe and Clark’s Grebe pairs.

These two species also breed widely thought the western United States, southern Canada and northern and central Mexico with large numbers in the Klamath Basin of Oregon and California, Washington, western Idaho, northern Utah, central North Dakota and central California. Canadian and United States populations winter on the Pacific Coast as far north as southeast Alaska, in the southwest United States and in northwest Mexico (Storer and Nuechterlein 1992a, b, Howell and Webb 1995, Am. Ornithol. Union 1998, Sauer et al. 2007).

SEASONAL OCCURRENCE. These species winter in Texas primarily in the Trans-Pecos, from September 30 to May 27 when they are common to uncommon (Western Grebe) and uncommon to rare (Clark’s; Oberholser 1974, Lockwood and Freeman 2004).In Arizona most breeding observations of Western and Clark’s grebes were obtained from mid April through July although at low elevations these species can breed any month of the year (Wise-Gervais 2005a, b). A lengthy breeding season was also found in eastern Colorado, April 29 to August 1 (Righter 1998a, b).

BREEDING HABITAT. These grebes breed in colonies on freshwater lakes and reservoirs surrounded by emergent vegetation (cattails, rushes, sedges) in Colorado, Arizona and other western states. (Harrison 1979, Righter 1998a, b, Wise-Gervais 2005a, b).

Nests are closely spaced, solid mounds of dry or sodden vegetation. anchored to plants or roots in water 0.6-3 m (2-10 ft) deep. The outside diameter ranges from 46 to 64 cm (18-26 in) and inside diameter 18-23 cm (7-9 in). The height above water is 8-13 cm (3-5 in; Harrison 1979, Storer and Nuechterlein. 1992a, b).

The female usually lays 3-4 (range 2-7) dull bluish white to cream eggs which turn buff or brown from staining in the nest (see photo of nest and eggs in Harrison [1979]). Egg laying may start before the nest is complete. Incubation by both parents begins after the first egg is laid and lasts 24 days. The young leave the nest on their parents’ back on the day they hatch, sometimes before the last egg hatches. The young continue to be brooded on their parents’ backs for 2-4 weeks with the non-brooding parent bringing food. Flight feathers of young birds are fully grown by 70 days .Only one brood is reared per season (Harrison 1979, Storer and Nuechterlein. 1992a, b).

STATUS. The winter populations of these grebes in Trans-Pecos, described as scarce and local by Oberholser (1974) increased steadily during the 1990s with some beginning to remain over the summer (Lockwood and Freeman 2004). North American Breeding Bird Survey data from 1980-2006 suggest an annual population change of  +1.7% for North America for this period (Sauer et al. 2007). These data are encouraging for the future of these species in Texas.Text by Robert C. Tweit (2008)

Literature cited.

American Ornithologists’ Union. 1998. Checklist of North American birds, 7^th ed. Am, Ornithol. Union, Washington, DC.

Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.

Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, New York.

Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.

Oberholser, H. C. 1974. The bird life of Texas. University of Texas Press, Austin.

Righter, R. 1998a. Western Grebe (Aechmophorus occidentalis). In Colorado breeding bird atlas, pp. 44-45 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.Righter, R. 1998b. Clark’s Grebe (Aechmophorus clarkii). In Colorado breeding bird atlas, pp. 46-47 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.

Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 7.23.2007. USGS Patuxent Wildlife Research Center, Laurel MD < http://www.mbr-pwrc.usgs.gov/bbs>

Storer, R. W. and G. L. Nuechterlein. 1992a. Western Grebe (Aechmophorus occidentalis). The Birds of North America Online (A. Poole Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from :http://bna.birds.cornell.edu/bna/species/026a

Storer, R. W. and G. L. Nuechterlein. 1992b. Clark’s Grebe (Aechmophorus clarkii), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from: http://bna.birds.cornell.edu/bna/species/026b

Wise-Gervais, C. 2005a. Western Grebe (Aechmophorus occidentalis). In Arizona breeding bird atlas. pp. 96-97 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.

Wise-Gervais, C. 2005b. Clark’s Grebe (Aechmophorus clarkii). In Arizona breeding bird atlas. pp. 98-99 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.