In the winter, Pied-billed Grebes (Podilymbus podiceps) are in their duller, non-breeding plumage.
These aquatic birds can be identified by their small size, white-ringed eyes, and broad, usually black-ringed bills. When they are in their non-breeding plumage, their black bill rings may become very faint and difficult to see.
Pied-billed Grebes are solitary and don't travel in large flocks. They rarely fly and will instead usually escape by diving under water and swimming away. Pied-billed Grebes prefer fresh water, and I observed this one at the Sweetwater Wetlands here in Tucson.