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Black-footed ferret
The black-footed ferret (''Mustela nigripes''), also known as the American polecat〔Heptner, V. G. (Vladimir Georgievich); Nasimovich, A. A; Bannikov, Andrei Grigorevich; Hoffmann, Robert S. (2001). (''Mammals of the Soviet Union'' ) Volume: v. 2, pt. 1b. Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation.〕 or prairie dog hunter, is a species of mustelid native to central North America. It is listed as endangered by the IUCN, because of its very small and restricted populations. First discovered by Audubon and Bachman in 1851, the species declined throughout the 20th century, primarily as a result of decreases in prairie dog populations and sylvatic plague. It was declared extinct in 1979 until Lucille Hogg's dog brought a dead black-footed ferret to her door in Meeteetse, Wyoming in 1981.〔(Black-footed Ferret Recovery Implementation Team ). Blackfootedferret.org. Retrieved on March 22, 2013.〕 That remnant population of a few dozen ferrets lasted there until the animals were considered extinct in the wild in 1987. However, a captive breeding program launched by the United States Fish and Wildlife Service resulted in its reintroduction into eight western states and Mexico from 1991–2008. There are now over 1,000 mature, wild-born individuals in the wild across 18 populations, with four self-sustaining populations in South Dakota (two), Arizona and Wyoming.〔
The black-footed ferret is roughly the size of a mink, and differs from the European polecat by the greater contrast between its dark limbs and pale body and the shorter length of its black tail-tip. In contrast, differences between the black-footed ferret and the steppe polecat of Asia are slight, to the point where the two species were once thought to be conspecific.〔 The only noticeable differences between the black-footed ferret and the steppe polecat are the former's much shorter and coarser fur, larger ears, and longer postmolar extension of the palate.〔
It is largely nocturnal and solitary, except when breeding or raising litters.〔〔 Up to 91% of its diet is composed of prairie dogs.〔〔
==Evolution==
Like its close cousin, the Asian steppe polecat (with which it was once thought to be conspecific), the black-footed ferret represents a more progressive form than the European polecat in the direction of carnivory.〔 The black-footed ferret's most likely ancestor was ''Mustela stromeri'' (from which the European and steppe polecat are also derived), which originated in Europe during the Middle Pleistocene. Molecular evidence indicates that the steppe polecat and black-footed ferret diverged from ''Mustela stromeri'' sometime between 500,000 and 2,000,000 years ago, perhaps in Beringia. The species appeared in the Great Basin and the Rockies by 750,000 years ago. The oldest recorded fossil find originates from Cathedral Cave, White Pine County, Nevada, and dates back to 750,000–950,000 years ago.〔 Prairie dog fossils have been found in six sites where ferrets are yielded, thus indicating that the association between the two species is an old one.〔 Anecdotal observations and 42% of examined fossil records indicated that any substantial colony of medium- to large-sized colonial ground squirrels, such as Richardson's ground squirrels, may provide a sufficient prey base and a source of burrows for black-footed ferrets. This suggests that the black-footed ferret and prairie dogs did not historically have an obligate predator-prey relationship. The species has likely always been rare, and the modern black-footed ferret represents a relic population. The earliest reported occurrence of the species is from a late Illinoian deposit in Clay County, Nebraska, and is further recorded from Sangamonian deposits in Nebraska and Medicine Hat. Fossils have also been found in Alaska dating from the Pleistocene.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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