nest poles have been erected to facilitate nesting. The Milk River is also home to many pond and wetland birds, and the grasslands are sharp-tailed grouse (Pedioecetes phasianellus) dancing grounds, or leks. Sharp-tailed grouse also appear to be declining in Alberta and are considered a sensitive species due to the increase of land-use conversion to agriculture. Mammals Until the late 1800s, large herds of bison grazed the area until they were extirpated by human hunting, and cattle have — to a degree — taken their place as grazers, maintaining the grassland ecosystem in a mix of grazed and ungrazed patches. Pronghorn (Antilocapra Americana) and mule deer (Odocoileus hemionus) are also present on the grasslands along with deer mice, voles, and Richardson's ground squirrel, an important food source for the ferruginous hawk and occasional burrow host to the burrowing owl. The formerly extirpated and subsequently reintroduced swift fox (Vulpes velox), currently listed as endangered provincially and downgraded to threatened nationally in 2009, is resident as well. Swift foxes were originally abundant across the prairies, but population declines caused by land use conversion, trapping, hunting, predation by domestic dogs, competition with coyotes, and rodent control programs led to their elimination from Alberta in 1938 and declared extirpated in 1978. The swift fox was reintroduced to Canada in 1983 from the progeny of a captive breeding program using Colorado and South Dakota stock, a controversial but relatively successful initiative. The current population is estimated at 647 foxes in Canada as of 2006, but predation by coyotes and golden eagles continues to be a limiting factor, with golden eagles causing 75% of the deaths of swift foxes in 1997. In addition, due to their small size and inability to see above tall vegetation, and their avoidance of agricultural lands and the associated chemical spraying which reduces their insect prey, swift foxes appear to be habitat specialists preferring shortgrass native prairie and land use conversion to agriculture is a continued threat. The area's woodland habitat is home to a herd of elk, along with porcupines, cottontail rabbits, and white-tailed deer. The badlands area of habitat in the Milk River Natural Area is host to bobcats (Lynx rufus), listed as sensitive, and scorpions (Paruroctonus boreus). Fish The area features three rare fish species: the venomous stonecat (Noturus flavus), the only catfish species in Alberta, St. Mary's Sculpin (Cottus bairdi punctulatus), and the western silvery minnow (Hybognathus