Canis lupus baileyi, a Mexican subspecies of grey wolf, is one of the most endangered canids in the world.  Historically, it occurred over a wide area of northern Mexico and the southern regions of Arizona, New Mexico, and Texas.  Like so many other subspecies of grey wolves, it fell prey to persecution by man.  Poisoned baits were in use by the mid-1800s throughout most of the grey wolf's southern range.  In 1976, the US Fish and wildlife service declared the the Mexican wolf an endangered species.  Afterward, a small number of facilities in the US began a captive breeding effort.  This has proved fairly successful, and there are now approximately 150 Mexican grey wolves in various zoos and wolf sanctuaries.