Coots are small to medium-sized duck-like waterbirds that belong to the genus Fulica and family Rallidae. They are found across most of the world and while there are several species, the most widespread is the Eurasian or common coot (Fulica atra). Coots have distinctive white frontal shields above their black heads and reddish-brown bodies. Their toes have lobed flaps of skin that allow them to swim and walk on vegetation. So what are coots’ closest living relatives?
Coots Belong to the Rail and Crake Family Rallidae
Coots belong to the family Rallidae which includes rails, gallinules, moorhens, and crakes. This diverse family contains around 150 species found across the world. All members of the Rallidae are marsh birds adapted to wetland environments. They have long necks, rounded non-webbed wings, and range in size from small crakes to large swamphens. Coots share a number of characteristics with other Rallidae:
- Slender bodies adapted for squeezing through dense vegetation
- Long toes for walking on floating vegetation
- Forehead shields or facial wattles
- Chicks that are precocial and able to feed themselves soon after hatching
So while coots have their own distinctive genus Fulica, their closest relatives are considered to be the other members of the rail and crake family Rallidae.
DNA Evidence Confirms Rallidae Relationships
In the last few decades, DNA analysis has helped clarify and confirm the evolutionary relationships between coots and other Rallidae species. By comparing genetic sequences, scientists can determine how recently different species shared a common ancestor. DNA evidence generally supports the grouping of coots within the Rallidae:
- A 2014 study found Eurasian coots to be most closely related to moorhens and swamphens, with all three sharing a common ancestor around 25 million years ago.
- Another analysis found that coots diverged from a lineage leading to crakes and rails around 50 million years ago.
- Mitochondrial DNA analysis has identified the red-knobbed coot and Andean coot as the Eurasian coot’s two closest living relatives.
While minor adjustments are still being made, most experts agree that DNA evidence confirms the close evolutionary ties between coots and other marsh-dwelling Rallidae like gallinules, moorhens, and swamphens.
Moorhens Are Considered Coots’ Closest Extant Relatives
Based on anatomy, behavior, and DNA relationships, most ornithologists identify moorhens as coots’ closest living relatives. There are four species of moorhen:
- Common moorhen (Gallinula chloropus)
- Lesser moorhen (Paragallinula angulata)
- Tasmanian nativehen (Gallinula mortierii)
- Allen’s gallinule (Porphyrio alleni)
Moorhens share a similar swamp-dwelling ecological niche to coots and have number of physical and behavioral similarities such as:
- Foraging on aquatic vegetation
- Nesting in reeds and rushes
- Head bobbing displays
- Dark plumage with white undertail coverts
The two groups are not identical however. Moorhens tend to have greenish legs whereas coots have white shields above the bill. Recent genetic studies confirm moorhens and coots share a common ancestor as little as 25 million years ago, supporting their close relationship.
Other Close Rallidae Relatives
While moorhens are their closest cousins, coots are also closely related to other marshbirds in the family Rallidae:
Swamphens
Swamphen is the common name for roughly 6 species of the genus Porphyrio including the purple swamphen and takahe. Swamphens and coots overlap extensively in their wetland habitat and diet. They diverged around 25 million years ago.
Gallinules
Gallinules are medium-sized marshbirds found worldwide. They include the common gallinule, azure gallinule, and purple gallinule. Gallinules resemble a cross between moorhens and coots and likely share a common ancestor with them around 25 million years ago.
Crakes
Crakes are small and slender marshbirds in the genus Porzana and elsewhere. While more terrestrial than coots, they occupy similar wetland habitats worldwide. Molecular evidence suggests crakes and coots diverged around 50 million years ago but still retain common anatomical traits.
Rails
Rails are a diverse group of small to medium-sized marshbirds found worldwide. Notable species include the Virginia rail, sora, yellow rail, and clapper rail. Most are more secretive than coots but DNA evidence confirms they share a common Rallidae ancestor.
Conclusion
In summary, while coots have their own distinctive genus, they are closely related to other marshbirds in the family Rallidae. Based on anatomy, behavior, habitat, and DNA evidence, coots’ closest living relatives are considered to be moorhens. However, they also retain close evolutionary ties to other wetland Rallidae like swamphens, gallinules, crakes, and rails. Coots and these other marshbirds share common adaptations for swimming, walking on vegetation, and nesting in wetlands.