Western grebe fossils from the Late Pleistocene of southwest North America were described as a distinct species,[4] but later ranked as a paleosubspecies Aechmophorus occidentalis lucasi.

It is easily confused with Clark's grebe, which shares similar features, body size, behavior and habitat, and hybrids are known.

Western Grebe nests are made of plant debris and sodden materials, and the nest-building begins roughly around late April through June.

Its subspecies, Clark's grebe generally populate more of the southern part of North America [12] Other differences are whiter flanks and paler gray backs when comparing A.o.clarkii to A.o.occidentalis.

In 1963 Dickerman reinstated the taxon as Aechmophorus clarkii, which he defined as the smaller birds, both dark and pale coloured, from Mexico.

In 1979 a comprehensive study by Ratti demonstrated the apparent existence of reproductive barriers between different phases of the grebes.

[13] This type of assortative mating derives from possible isolating mechanisms such as differential responses to advertising calls and spatial distribution.

[13][16] Each of the forms tended to stay closer to their own type, thus making their colony nesting be non-randomly distributed.

The birds lift their wings stiffly to the side and run in an upright position with its head held forward and neck curved.

[22] However it is also stated brood size of nests that hatched later in the season is larger than those from earlier, which contradicts previous findings.

Ecological constraints also pressure the young, and this may lead to siblicide in the first weeks after hatching, which may explain the brooding differences.

This shows the predation or even the seemingly threatening acts result in a decrease of reproduction and survival of the young.

[23] Because they are so sensitive, there have been restoration efforts to rebuild the Western grebes' native habitats, so that they have greater opportunity to reproduce and raise their young without disturbance or threat.

The number of Grebes has been slowly declining in the last two decades, not only because of predation, but also because of habitat destruction, with oil spillage being one of the major causes.