Since the initial releases on Norias Division of King Ranch during the first half of the 20th century, nilgai antelope (Boselaphus tragocamelus) have proliferated to occupy a portion of the Gulf Coastal Prairies and Marshes region of southern Texas located between Baffin Bay and the mouth of the Rio Grande River and south into Mexico (Sheffield 1984, Mungall 1994). Although there are isolated populations in other areas of Texas, the aforementioned area is their primary range in Texas (Sheffield 1984, Mungall 1994). Nilgai herds in this area are very prolific, and their densities often exceed those of native ungulates (El Sauz Ranch, unpubl. data).
In southern Texas, nilgai are primarily grazers (Sheffield 1984). However, nilgai require a higher quality diet than can be provided exclusively by grazing and must consume more forbs and browse than cattle (Mungall 1994). As the quality and quantity of available grass declines, nilgai readily increase consumption of forbs and browse (Mungall 1994). Nilgai are large animals and, therefore, have high consumption rates (Abrams 1990). This creates a myriad of concerns for the modern range manager operating in this portion of southern Texas.
Because of their large size and high consumption rate, nilgai antelope may displace other animals and dominate areas of higher quality habitat. Grazing activity of nilgai may compete directly with domestic livestock, thus affecting appropriate stocking rates. Their ability to shift their diet from grass to browse and forbs combined with their ability to browse higher into trees and shrubs may give them a competitive edge over native ungulates such as white-tailed deer (Odocoileus virginianus) (Sheffield 1984).
The objectives of this study are to determine home range sizes of nilgai; determine whether nilgai utilize available habitats at random; rank available habitats in order of preference; compare use of available habitats by male and female nilgai; relate use of available habitats by nilgai to season, temperature, water availability and grazing of domestic cattle; and to examine the effects of habitat on movement and home range size of nilgai. We will test the following hypotheses: (1) Nilgai will concentrate in areas that have been deferred from grazing by domestic cattle; (2) Nilgai will emigrate from pastures that have been deferred from grazing upon the return of domestic cattle; (3) Nilgai in areas of relatively low quality habitat will exhibit larger home ranges than nilgai in areas of relatively high quality habitat; (4) Nilgai will migrate in response to water availability.