Clark's grebe (Aechmophorus clarkii ) is a North American waterbird species in the grebe family. Until the 1980s, it was thought to be a pale morph of the western grebe, which it resembles in size, range, and behavior. Intermediates between the two species are known.
This species nests on large inland lakes in western North America and migrates to the Pacific coast over the winter. It maintains local populations year-round in California, Nevada, and Arizona (the Lower Colorado River Valley), as well as in central Mexico. It feeds by diving for insects, polychaete worms, crustaceans, and salamanders.
It performs the same elaborate courtship display as the western grebe.
The "Clark" of its common name—and its specific epithet clarkii —honors John Henry Clark, a 19th-century American surveyor who was also a naturalist and collector. The genus name Aechmophorus comes from the Ancient Greek words αἰχμά (transliterated "aichme"), meaning 'point of a spear', and φόρος ("phoros"), meaning 'bearing'; together translating as 'spear point bearer' and referring to the bird's long, dagger-like beak.
In Mexico it is called achichilique pico naranja (the western grebe is called the achichilique pico amarillo ). A common name advocated in Spain for this bird is the calque achichilique de Clark.
Clark's grebe closely resembles the western grebe and occurs in the same colonies together with it. Storer and Nuechterlein in 1992, following earlier morphological studies by Storer and others, define the species as being distinguished from the western grebe by an overall paler plumage on its back, as well as a larger portion of its face covered in white, as it extends above the eyes, rather than just below them. A distinguishing feature is its bill, which is bright yellow in the US, whereas the Western Grebe's bill is greenish-yellow in the US, which had been noted by others. Storer and Nuechterlein in 1992 claim that the bill is slightly upturned in this species whereas the western grebe has a straight bill, this was not noted in earlier studies.
The grebe has a long, slender neck and the species ranges in size from 22–29 inches (56–74 cm), with a wingspan of 24 inches (61 cm). The Clarks' grebe has a weight range of 25.3–44.4 oz (720–1,260 g).
There are few changes between the sexes, the most notable feature that distinguishes males from females is the presence of a slight crest on the heads of males. In juveniles, the plumage is again similar to the Western Grebe, however it is also paler compared to the greyer Western species.
Its relative size compared to the western grebe is confused. Dickerman showed that grebes from the south of the range were smaller than northern examples, irrespective of which color morph, with both morphs being the same size depending on location, and Dickerman originally reinstated the name A. clarkii in 1963 for the smaller, southern populations (irrespective of which color morph). Studies by Storer, Ratti, Mayr and Short in the 1960-70s did not find any size differences between morphs. Nonetheless, some publications now state the paler-coloured grebes are slightly smaller, which might be due to confusion with the species concept advocated by Dickerman (in which Clark's grebe doesn't not occur in the USA or Canada, pale-coloured grebes in the US and Canada are western grebes, and dark-colored morphs in Mexico are Clark's grebe).
Although darker and lighter-colored morphs of grebes occur in the resident non-migratory populations occur in Mexico, it is unclear if these can be distinguished by the other morphological characteristics described above, as most studies have only looked at US populations. Lighter-colored morphs in Mexico are said to have orange-coloured bills, and the darker morphs have yellow bills. In the winter in California numerous examples of dark-colored western grebes displayed the mostly white face of Clark's grebe, although this was intermediate and thought to be possibly due to seasonal changes.
Being waterbirds, they require bodies of water that offer the necessary food and shelter that they need to thrive—usually lakes or suitable wetlands—that are also in proximity to suitable tree cover that they can use for nesting.
Clark's grebes occur seasonally throughout the majority of Western America, with a distribution ranging as far south as Mexico, and reaching as far north as British Columbia and Saskatchewan. They avoid the cold and are only found in central USA and Canada during the summer breeding season. In the US and Canada breeding is done across a large portion of the west of these two countries, spanning from British Columbia to Texas, for which the grebes tend to favour larger bodies of water and congregate in large flocks.
Storer and Nuechterlein in 1992 dubiously claim the birds winter in Central America, as well as in Mexico and some regions of California. Out of almost 100,000 records of this taxon logged at the Global Biodiversity Information Facility there are zero records found south of northern Oaxaca, Mexico.
The range of this bird in Mexico is distributed in two streaks southward; one from the California border along the Pacific coast throughout Baja California and across the gulf along the coast to southern Sonora, the other a higher altitude, inland distribution running down from the Big Bend region behind the Texas border down the mountains of central Mexico, with the highest concentration in population in the south from Jalisco to Puebla and northern Oaxaca, where the distribution abruptly ceases. These two distributional areas representing where grebes have ever been seen only meet each other in the very north of Mexico in a strip along the USA border, to the south they do not come together and are separated by a very large distance. It is completely absent from the Atlantic coast.
Thought to be a fish specialist in the early 20th century as a result of the examination of their pellets and stomach contents, it was shown by 1962 that Clark's grebe is actually an opportunist when it comes to the food it eats, and is less picky with its selection than previously imagined. This means that the species will actually consume a wide variety of things such as salamanders, crustaceans, polychaete worms and insects while diving and foraging for their preferred small fish, so long as they fit the size constraints of the bill.
Clark's grebes appear to have semi-monogamous behavior, staying with a single mate, but possibly only for a single season as far as known. Unpaired males far outnumber the females. Males, while they stay with their mate until at least a few weeks after the hatching of their young, will have several sexual partners in their lifetime. It is less known if pairs will eventually mate again in the future. There are two courtship ceremonies that are performed before selection and mating take place: the "rushing ceremony" and the "weed ceremony". They entail a sequence of performances and advertisements/dances with the partner, or presenting the partner with a bundle of weeds and performing a different set of dances, respectively. As there are fewer females than males, the final decision of whether or not mating occurs depends on the females. Therefore, there is a level of sexual selection within the species. These courtships take place during spring migration and shortly after arriving on the breeding grounds.
It is important to note that while there are very few cases of breeding between clark's and western grebes, there have been cases where phenotypic hybrids (birds with plumage that is similar to both species) have mated and produced fertile offspring. It is believed, however, that this becomes less likely when the individuals are from different migrations and are not hybrids, as they have a greater chance of failing during the courtships.
