Why this bird is called a "turkey"

There are two theories for the derivation of the name "turkey" for this bird, according to Columbia University professor of Romance languages Mario Pei. One theory is that when Europeans first encountered turkeys in America, they incorrectly identified the birds as a type of guineafowl, which were already being imported into Europe by Turkey merchants via Constantinople and were therefore nicknamed Turkey coqs. The name of the North American bird thus became "turkey fowl" or "Indian turkeys," which was then shortened to just "turkeys".
The other theory arises from the fact that turkeys came to England from the Americas via merchant ships from the Middle East where they were domesticated successfully. Again the importers lent the name to the bird: because these merchants were called "Turkey merchants" as much of the area was part of the Ottoman Empire. Hence the name “Turkey birds” or, soon thereafter, “turkeys”.
In many countries, the names for turkeys have different derivations. Ironically, many of these names incorporate an assumed Indian origin, such as diiq Hindi ("Indian rooster") in Arabian countries, dinde ("from India") in French, Indjushka ("bird of India") in Russia, indyk in Poland, and Hindi ("India") in Turkey. These are thought to arise from the thought that Christopher Columbus had originally believed that he had reached India rather than the Americas on his voyage. In Portuguese a turkey is a peru; the name is thought to derive from the eponymous country Perú.
Several other birds that are sometimes called turkeys are not particularly closely related: the brushturkeys are megapodes, and the bird sometimes known as the "Australian turkey" is the Australian bustard (Ardeotis australis). The anhinga (Anhinga anhinga) is sometimes called a water turkey, from the shape of its tail when the feathers are fully spread for drying.