Western Grebe Aechmophorus occidentalis Scientific name definitions

The Western Grebe is a conspicuous waterbird of western North America that ranges from southern Canada to the Mexican Plateau. This species is closely related to the Clark's Grebe (Aechmophorus clarkii), and formerly classified as conspecific with it, in that Clark's was viewed as only a “white morph” of the Western Grebe (but see Systematics History). Evidence for the renewed specific status of Western Grebe began with finding that Western and Clark's grebes mated assortatively (1 Storer, R. W. (1965). The color phases of the Western Grebe. Living Bird 4:59-63. Close ), and an analysis of DNA-DNA hybridization (2 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 (A.occidentalis) and Clark's Grebe (A. clarkii), as indicated by DNA-DNA hybridization. Postilla 200:1-7. Close ) indicated that the median DNA sequence distance between the species was comparable to such distances between other congeners. Despite broad sympatry, intermediates (i.e., suspected hybrids) between the species apparently are rare, as are mixed pairings (1 Storer, R. W. (1965). The color phases of the Western Grebe. Living Bird 4:59-63. Close , 3 Ratti, J. T. (1979). Reproductive separation and isolating mechanisms between sympatric dark- and light-phase Western Grebes. Auk 96:573-586. Close ); the species may interbreed as frequently as they do in areas of relative allopatry, implying adaptive mate choice (4 Konter, A. (2012). Visual assessment of interbreeding by Aechmophorus grebes. Wilson Journal of Ornithology 124 (4):713-720. Close ).

Western Grebe and Clark's Grebe are perhaps best known for their elaborate and energetic courtship rituals. These courtship ceremonies—in which courting pairs perform a series of displays in ritualized, apparently mechanical, sequences—are among the most complex known in birds. These two species are unique among grebes in possessing a mechanism in the neck that permits them to thrust forward the head like a spear. Such a mechanism is well known in herons (Ardeidae) and the anhingas (Anhingidae), but the details have not been studied in Aechmophorus grebes.

Because Western Grebe and Clark's Grebe were from 1886 until 1985 considered color phases of the Western Grebe, the literature on the two species was combined under that name. Only rarely was mention made of the “phase” of the birds studied. Because of this, and because of the great similarity between the two species in morphology and behavior, this account contains references that may pertain to both species. In the account, information known to apply specifically to the Western Grebe is given first, followed by information common to both species, and that for which the “phase” was not mentioned.

There are two subspecies of Western Grebe: A. o. occidentalis breeds in southwestern Canada and the United States, whereas A. o. ephemeralis is resident on the Mexican Plateau. Although the behavior of the northern subspecies is relatively well studied, little is known of their longevity and movements, owing to a paucity of banding recoveries. Parallel studies on the biology of the Mexican subspecies could aid our understanding of the evolution of Aechmophorus grebes.