Podicipediformes

Small or medium-sized diving birds, grebes spend almost all their time on the water. They are found on lakes and marshes across the world, but reaching their greatest diversity in the New World.

Additional information

Grebes are almost entirely aquatic, leaving water only to access their nest. They rarely fly except to migrate. Short-winged Grebe (Rollandia microptera) is entirely flightless, as is Junín Flightless Grebe (Podiceps taczanowskii) and the probably-extinct Atitlan Grebe (Podilymbus gigas). The birds are generally uncomfortable on land, although Short-winged Grebe will make wing-assisted runs, sometimes over considerable distances. 

Most species are shy. If threatened, the birds can expel all the air from their body and sink rapidly; otherwise, they will either swim to the safety of shoreside vegetation or dive and swim away underwater.

Grebes form a monogamous pair bond lasting at least one breeding season; paris sometimes remain together during the winter. Courtship may be elaborate, involving highly ritualized displays. Great Crested Grebes (Podiceps cristatus) has three main display behaviors: head shaking, 'discovery' (one bird approaches the other underwater and emerges in front of it), and the weed ceremony. The birds are territorial during breeding season.

Taxonomy 

Number of genera: 6

Number of species: 22

A list of all species can be found here.