Of course they have ears, all birds do. These birds got that label for the spray of straw-colored feathers that males and females grow behind the eye and over the ear during breeding season. The “Eared Grebe” name is unique to North America; elsewhere the bird is known as the “black-necked grebe,” a literal translation of the scientific name, Podiceps nigricollis. (Wikipedia) The birds with plain grey and white heads are either nonbreeding adults or juveniles.
Eared Grebes are said to be “the most abundant grebe in the world.” (Cornell lab.) That may be, but we don’t see them very often around Chavez Park. The most recent images on this website date to almost exactly a year ago, when Eareds arrived in company of a Horned Grebe (who also don’t have horns); see “Horned and Eared” April 19 2020. To my knowledge, they’ve never gathered here in large numbers. They assemble by the thousands on salty lakes fat with brine shrimp, such as Mono Lake, the Salton Sea, or the Great Salt Lake in Utah.