Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae. There are six to seven species of swan in the genus Cygnus in addition there is another species known as the Coscoroba Swan, although this species is no longer considered related to the true swans. Swans usually mate for life, though ‘divorce’ does sometimes occur, particularly following nesting failure. The number of eggs in each clutch ranges from three to eight.
The wild horse is a species of the genus Equus, which includes as subspecies the domesticated horse as well as the undomesticated Tarpan and Przewalski’s Horse. The Tarpan became extinct in the 19th century, and Przewalski’s Horse was saved from the brink of extinction and reintroduced successfully to the wild. The most likely ancestor of the domestic horse was the Tarpan, which roamed the steppes of Eurasia at the time of domestication.Since the extinction of the Tarpan, attempts have been made to reconstruct the phenotype of the Tarpan, resulting in horse breeds such as the Konik and Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, and therefore these breeds possess domesticated traits.