Editing Clark's grebe (section)

==Taxonomy==
Clark's grebe (''Aechmophorus clarkii'') is a waterbird of the family [[Podicipedidae]] in the order [[Podicipediformes]], which are related to [[flamingos]].<ref name=Jarvisetal>{{cite journal | last1=Jarvis | first1=E.D.| date=12 December 2014 | title=Whole-genome analyses resolve early branches in the tree of life of modern birds | journal=Science | volume=346 | issue=6215 | pages=1320–1331 | doi=10.1126/science.1253451 |display-authors=etal | pmid=25504713 | pmc=4405904| bibcode=2014Sci...346.1320J}}</ref>

=== History ===
This taxon is extremely similar to the western grebe: it has the same behaviour, including the elaborate courtship displays, occurs sympatrically in the same range and has the same migrations, and is morphologically almost alike, with this bird most noticeably being somewhat paler in colouration. The two taxa can even successfully cross-breed, with intermediates as a result. As such, it was commonly thought to be a paler-colored [[Polymorphism (biology)|morph]] (a version with paler colours and more white), as occurs in many bird species.<ref>{{cite web |url=http://www.fitzpatrick.uct.ac.za/fitz/research/programmes/understanding/colour_polymorphism |title=Understanding colour polymorphism in birds |author=<!--Not stated--> |date=2017 |publisher=FitzPatrick Institute of African Ornithology, University of Cape Town |access-date=25 November 2018}}</ref>

In 1858, the lighter-coloured morph had first been described as a separate Mexican and Californian species, ''Podiceps clarkii'' by [[George Newbold Lawrence|George N. Lawrence]]. Lawrence cited three specimens as representative of his new species, but did not cite a specific holotype. Of the three specimens Lawrence used, two were larger, migratory birds from California, whereas a single specimen was a smaller bird from Laguna Santa Maria in [[Chihuahua (state)|Chihuahua]]. Deignan designated this last specimen as the [[holotype]] in 1961.<ref name=Ratti1979/><ref name=Dickerman1986/>

After the presence of this taxon throughout the range of the western grebe was discovered, along with the identical behaviour, the two taxa were synonymised, and this situation was accepted by ornithologists throughout the first half of the 20th century.<ref name=Ratti1979/><ref name=Dickerman1986/>

According to Robert W. Storer, in 1965, besides the paler coloration, there were other more subtle morphological differences between the two taxa: the bill of the western grebe is greenish-yellow, whereas this grebe has a bright yellow bill, and furthermore the black color of the crown extends less far down for this grebe, with the black extending below the eye, the [[Lore (anatomy)|lores]] and the thin line of bare skin extending from the eye to the corner of the bill in the case of the western grebe, whereas in this grebe the black reaches somewhat less far, leaving a thin line of paler color above the eye. Subsequent studies also showed the frequency of lighter morphs appeared more common in the south of the range than in the north, being relatively common in Mexico according to studies by Dickerman in 1973, but rare in Canada according to Nero (1962) and Storer (1965).<ref name=Ratti1979/>

Dickerman in 1963 was the first to cast doubt on the taxonomic status of the taxon, believing that the synonymy was incorrect, and thus he moved Lawrence's ''Podiceps clarkii'' to ''Aechmophorus clarkii'', and restricted the distribution of this taxon to Mexico, rejecting Lawrence's identification of the larger-sized, pale-colored birds from California and elsewhere in the US and Canada as this taxon. His studies showed that there was little overlap in size measurements between Mexican and northern populations -irrespective of coloration; as such Dickerman's 1963 view was that ''A. clarkii'' are smaller grebes restricted to Mexico, which might be found in either light or dark morphs, and ''A. occidentalis'' are larger-sized, migratory grebes from the US and Canada also found in two colour morphs.<ref name=Dickerman1986/>
 
A study in 1979 based on late 1970s observations of pairs the birds courting or nesting, however, noted that the frequency with which two different colour morphs were seen together or were found nesting together was much lower than one would expect if the pairings were random, some reproductive isolating mechanism was keeping the taxa separate. It also found that although the birds inhabited the same wetlands and the same habitats, the populations were not randomly distributed, with the taxa preferentially nesting with their own morph, and colonies being in large part of one type or the other, despite that one morph was much rarer in frequency than the other. There was also a marked difference in reproductive success in the study area, with Clark's grebe being initially quite low in frequency at around 12%, but increasing to a third of the population of both taxa in a three-year period. The study used the black coloration of the crown to distinguish the two taxa, but it was noted that some grebes in California in the winter appeared to be the dark morph, but that the black of the crown reached less far -the lores being whitish, confusing this distinguishing feature.<ref name=Ratti1979/>

In 1986, Dickerman, accepting a taxonomically significant difference between the two colour morphs, described the taxa ''A. occidentalis'' ssp. ''ephemeralis'' for the smaller Western grebes of southern Mexico, and ''A. clarkii'' ssp. ''transitionalis'' for the larger migratory North American Clark's grebe subspecies sympatric with the nominate Western grebe subspecies. In this view, the nominate form of ''A. clarkii'' constituted smallish, pale-colored grebes from Mexico.<ref name=Dickerman1986/>

By 1992, Storer and Gary L. Nuechterlein, both having studied the grebes in the 1970s, recognised the paler-coloured morphs in the US and Canada in the book ''The Birds of North America'' as ''A. clarkii'', thus apparently rejecting Dickerman's species concept and subspecific classification, although they do not explicitly state this, and because this work does not include Mexico as part of North America, his work is not actually in their remit. Because of this, it is unclear if they consider the dark-coloured grebes of Mexico to be a morph of Clark's grebes, or to be smaller forms of western grebes.<ref name=Storer1992/>

=== Subspecies ===
Two subtaxa of grebe classified as [[subspecies]] of ''Aechmophorus clarkii'' were recognised in 1986:<ref name=Dickerman1986/>

*''A. c.'' ssp. ''clarkii'', <small>([[George Newbold Lawrence|Lawrence]], 1858)</small> - Smaller subspecies comparable to the sympatric subspecies of Western Grebe (''A. occidentalis ephemeralis'') from north & central Mexico. Nominate.
*''A. c.'' ssp. ''transitionalis'', <small>(Dickerman, 1986)</small> - Larger than nominate ''clarkii'', from Western North America between southeast Alaska south to north Mexico. <ref>{{Cite web|title=Aechmophorus clarkii (Clark's Grebe) - Avibase|url=https://avibase.bsc-eoc.org/species.jsp?avibaseid=D05FFEF7505D95C7|access-date=2021-10-25|website=avibase.bsc-eoc.org}}</ref>