These are the wild donkeys of Bonaire. It was thought that these were
ordinary donkeys, and an aggressive effort was made to capture and sterilize all of them.

Subsequent genetic testing has shown these to be the only remaining wild population in the world of an African Wild Donkey, the Nubian Ass.

A belated effort was made to preserve them, but only a few fertile individuals remain.
http://en.wikipedia.org/wiki/Nubian_wild_ass