GENETIC SUBSPECIES IDENTIFICATION OF A RECENTLY COLONIZED BIGHORN SHEEP POPULATION IN CENTRAL ARIZONA

Two subspecies of bighorn sheep currently occur in Arizona: the desert bighorn sheep (Ovis canadensis mexicana, O. c. nelsoni) and Rocky Mountain bighorn sheep (O. c. canadensis). In central Arizona (Game Management Unit 23 (GMU 23)), bighorn sheep colonized an area along the Salt River; however, the source of this population was enigmatic. Although the nearest desert bighorn sheep herd is <30 km to the southwest of the herd in Unit 23, no obvious movement corri- dors were evident between them. Rocky Mountain bighorn sheep from an earlier translocation occur about 160 km east of the herd in Unit 23, and these animals could have used the Salt River drainage as a movement corridor to colonize this new area. In an effort to clarify the subspecies affinity of big- horn sheep in the colonized area, we obtained mitochondrial DNA sequences (473-bp of the control region) from bighorn sheep in GMU 23 (n = 5), Rocky Mountain bighorn sheep as a reference (n = 8), and desert bighorn sheep references (n = 58). Our data provided strong support for the hypothe- sis that bighorn sheep in GMU 23 were of Rocky Mountain origin, suggesting that these sheep have moved about 160 km west along the Salt River drainage over the last 25 years. These data will facili- tate effective management of this herd to minimize its impact on neighboring native desert bighorn sheep populations. The future growth of this population could jeopardize the integrity of subspecific classifications in central Arizona. Given documented long-distance movements of males, sheep populations (including translocation programs) should be managed to maintain subspecific separa- tion.