Grebe


Grebes are aquatic diving birds in the order Podicipediformes. Grebes are widely distributed freshwater birds, with some species also found in marine habitats during migration and winter. Most grebes fly, although some flightless species exist, most notably in stable lakes. The order contains a single family, the Podicipedidae, which includes 22 species in six extant genera.
Although, superficially, they resemble other diving birds such as loons and coots, they are most closely related to flamingos, as supported by morphological, molecular and paleontological data. Many species are monogamous and are known for their courtship displays, with the pair performing synchronized dances across the water's surface. The birds build floating vegetative nests where they lay several eggs. About a third of the world's grebes are listed at various levels of conservation concerns—the biggest threats including habitat loss, the introduction of invasive predatory fish and human poaching. As such, three species have gone extinct.

Etymology

The word "grebe" comes from the French grèbe, which is of unknown origin and dates to 1766. It is possibly from the Breton krib meaning 'comb', this referring to the crests of many of the European species. However, grèbe was used to refer to gulls. The appearance of "grebe" in the English language was introduced in 1768 by the Welsh naturalist Thomas Pennant when he adopted the word for the family. Some of the smaller species are often referred to as "dabchick", which originated in the mid-16th century in English, as they were said to be chick-like birds that dive. The clade names "Podicipediformes" and "Podicipedidae" are based on the genus Podiceps which is a combination of Latin of podex, gen. podicis and pes, a reference to the placement of a grebe's legs towards the rear of its body.

Field characteristics

Grebes are small to medium-large in size ranging from the least grebe, at and, to the great grebe, at and. Despite these size differences, grebes are a homogeneous family of waterbirds with very few or slight differences among the genera.

Anatomy and physiology

On the surface of the water, they swim low with just the head and neck exposed. All species have lobed toes and are excellent swimmers and divers. The feet are always large, with broad lobes on the toes and small webs connecting the front three toes. The hind toe also has a small lobe. The claws are similar to nails and are flat. These lobate feet act as an oar, as when moving forward, they provide minimum resistance, and moving backwards, they provide maximum coverage.
The leg bones are equal in length, with the femur having a large head and the presence of long cnemial crests in the tarsometatarsus. The patella is separate and supports the tarsometatarsus posteriorly, which greatly helps with the contraction of the muscles. They swim by simultaneously spreading out the feet and bringing them inward, with the webbing expanded to produce the forward thrust in much the same way as frogs. However, due to the anatomy of the legs, grebes are not as mobile on land as they are on the water. Although they can run for a short distance, they are prone to falling over, since they have their feet placed far back on the body.
The wing shape varies depending on the species, ranging from moderately long to incredibly short and rounded in shape. The wing anatomy in grebes has a relatively short and thin carpometacarpus-phalanges component, which supports their primary feathers, while the ulna is long and fairly weak, supporting secondary feathers. There are 11 primaries and 17 to 22 secondaries, with the inner secondaries being longer than the primaries. As such, grebes are generally not strong or rapid fliers. Some species are reluctant to fly. Indeed, several have become flightless. In these flightless species, they tend to have a reduction in the length of their wings, tails, and primaries; reduced pectoral muscles, and a significant increase in body size. Since grebes generally dive more than fly, the sternum can be as small or even smaller than the pelvic girdle. When they do fly, they often launch themselves off from the water and must run along the surface as they flap their wings to provide a lift.
Bills vary from short and thick to long and pointed, depending on the diet, and are slightly larger in males than in females.

Feathers

Grebes have unusual plumage. On average, grebes have 20,000 feathers, the highest among birds. The feathers are very dense and strongly curved. In the larger species, feathers are denser but shorter, while the opposite is true in smaller species, where the feathers are longer but less dense.
The density and length of feathers are correlated exponentially with heat loss in cold water. For this reason, grebes invest the most time and effort of all birds in plumage maintenance. The uropygial glands secrete a high concentration of paraffin. The secretion provides a dual purpose of protecting the feathers from external parasites and fungi, as well as waterproofing them. When preening, grebes eat their feathers and feed them to their young. The function of this behaviour is uncertain, but it is believed to assist with pellet formation, excreting out internal parasites and protecting their insides from sharp bone material during digestion. The ventral plumage is the most dense, described as very fur-like. By pressing their feathers against the body, grebes can adjust their buoyancy. In the non-breeding season, grebes are plain-coloured in dark browns and whites. However, most have ornate and distinctive breeding plumages, often developing chestnut markings on the head area, and perform elaborate display rituals. The young, particularly those of the genus Podiceps, are often striped and retain some of their juvenile plumage even after reaching full size.

Systematics

The grebes are a radically distinct group of birds as regards their anatomy. Accordingly, they were at first believed to be related to the loons, which are also foot-propelled diving birds, and both families were once classified together under the order Colymbiformes. However, as early as the 1930s, this was determined to be an example of convergent evolution caused by the strong selective forces encountered by unrelated birds sharing the same lifestyle at different times and in various habitats. Grebes and loons are now separately classified orders of Podicipediformes and Gaviiformes, respectively.
One of the first incidents of the molecular placement of grebes among birds comes from Charles Sibley and Jon E. Ahlquist, who conducted DNA–DNA hybridization studies in the late 1970s and throughout the 1980s. They found the family to occupy a basal position in a clade that also includes the totipalmates, wading birds, New World vultures, loons, penguins, and tubenosed seabirds. Subsequent molecular studies have not supported this arrangement, however. These subsequent molecular studies instead have suggested a relation with flamingos, a finding that has been backed up by morphological evidence. They hold at least eleven morphological traits in common that are not found in other birds. For example, both flamingos and grebes lay eggs coated with chalky amorphous calcium phosphate. Many of these characteristics have been previously identified in flamingos, but not in grebes. For the grebe-flamingo clade, the taxon Mirandornithes has been proposed. Alternatively, they could be placed in one order, with Phoenocopteriformes taking priority.

Fossil record

The fossil record of grebes is incomplete, as there are no transitional forms between more conventional birds and grebes known from fossils. The enigmatic waterbird genus Juncitarsus, however, may be close to a common ancestor of flamingos and grebes. The extinct stem-flamingo family Palaelodidae has been suggested to be the transitional linkage between the filter-feeding flamingos and the foot-propelled diving grebes. The evidence for this comes from the overall similarity between the foot and limb structure of grebes and palaeloids, suggesting the latter family of waterbirds was able to swim and dive better than flamingos. Some early grebes share similar characteristics to the coracoid and humerus seen in palaeloids.
True grebes suddenly appear in the fossil record in the Late Oligocene or Early Miocene, around 23–25 mya. There are a few prehistoric genera that are now completely extinct. Thiornis and Pliolymbus date from a time when most if not all extant genera were already present. Because grebes are evolutionarily isolated and they only started to appear in the Northern Hemisphere fossil record in the Early Miocene, they are likely to have originated in the Southern Hemisphere.
  • Genus Aechmophorus Coues, 1862
  • * †Aechmophorus elasson Murray, 1967
  • Genus †Hunucornis Agnolín et al., 2025
  • * †Hunucornis huayanen Agnolín et al., 2025
  • Genus †Miobaptus Švec, 1982
  • * †Miobaptus huzhiricus Zelenkov, 2015
  • * †Miobaptus walteri Švec, 1982
  • Genus †Miodytes Dimitreijevich, Gál & Kessler, 2002
  • * †Miodytes serbicus Dimitreijevich, Gál & Kessler, 2002
  • Genus †Pliolymbus Murray, 1967
  • * †Pliolymbus baryosteus Murray, 1967
  • Genus Podiceps Latham 1787
  • * †Podiceps arndti Chandler, 1990
  • * †Podiceps csarnotanus Kessler, 2009
  • * †Podiceps discors Murray, 1967
  • * †Podiceps dixi Brodkorp, 1963
  • * †Podiceps howardae Storer, 2001
  • * †Podiceps miocenicus Kessler, 1984
  • * †Podiceps oligoceanus
  • * †Podiceps parvus
  • * †Podiceps pisanus
  • * †Podiceps solidus Kuročkin, 1985
  • * †Podiceps subparvus
  • Genus Podilymbus Lesson 1831
  • * †Podilymbus majusculus Murray 1967
  • * †Podilymbus wetmorei Storer 1976
  • Genus †Thiornis Navás, 1922
  • * †Thiornis sociata Navás, 1922
A few more recent grebe fossils could not be assigned to modern or prehistoric genera:
  • Podicipedidae gen. et sp. indet. – formerly included in Podiceps parvus
  • Podicipedidae gen. et sp. indet. UMMP 49592, 52261, 51848, 52276, KUVP 4484
  • Podicipedidae gen. et sp. indet.
  • Podicipedidae gen. et sp. indet. UMMP 74784