Editor’s Note (August 2016): Maps, rich media, and text have been updated to reflect a taxonomic change/split for this species. This species account is still being edited and may contain content from an earlier version of the account.
Clark's Grebe closely resembles the Western Grebe and was long considered a color morph of it. The nomenclatural history of the two is included in the introduction to the Western Grebe. Evidence for the renewed specific status of Clark's Grebe began with finding that Western (Aechmophorus occidentalis) and Clark's grebes mated assortatively (Storer 1965). A detailed study of the relationships between the two species was made by Ratti (Ratti 1979), who also provided material for an analysis of DNA-DNA hybridization (Ahlquist et al. 1987). This analysis indicated that the median DNA sequence distance between the species was “comparable to such distances between other closely related congeneric species,” although it was less than the distance between the pair subspecies on their table. Nuechterlein (Nuechterlein 1981c) demonstrated that a difference in the number of notes in the Advertising call was important in reproductive isolation of the two species.
Because the two species were not separated in the earlier literature, the accounts covering both species are given in the biography of the Western Grebe. Only accounts applying to Clark's Grebe and to observed differences between the species are given here.