The phrase "As bald as a coot" refers to which type of animal that has the appearance of baldness on its head?

Coots are rather small water birds that are members of the rail family, "Rallidae". They constitute the genus "Fulica", the name being the Latin term for "coot". Coots have predominantly black plumage, and—unlike many rails—they are usually easy to see, often swimming in open water. They are close relatives of the moorhen.

Coots have prominent frontal shields, with red to dark red eyes and coloured bills. The featherless shield gave rise to the expression "as bald as a coot," which the Oxford English Dictionary cites in use as early as 1430. Like other rails, they have long, lobed toes that are well adapted to soft, uneven surfaces. Coots have strong legs and can walk and run vigorously.

The greatest species variety occurs in South America. They are also common in Europe and North America. Coot species that migrate do so at night. The American coot has been observed rarely in Britain and Ireland, while the Eurasian coot is found across Asia, Australia and parts of Africa. In southern Louisiana, the coot is referred to by the French name "poule d'eau", which translates into English as "water hen" or "moorhen".

Coots are omnivorous, eating mainly plant material, but also small animals, fish and eggs. They are aggressively territorial during the breeding season, but are otherwise often found in sizeable flocks on the shallow vegetated lakes they prefer.