Department staff carrying Kofa bighorn from capture helicopter

Since the 1950s, translocation of bighorn sheep has been the primary means to reestablish populations in historical and unoccupied habitat, and to supplement dwindling populations.  Research published in 2001 reviewed 100 translocations within six western states between 1923 and 1997 and found that 41% were successful.  Successful translocations were defined as the establishment of a population of >100 individuals, because one hundred animals is considered the minimum number required to assure a high probability of survival for the next 100 years.  Some transplants have failed entirely due to heavy predation or unknown causes.  Many transplants in the western U.S. have consisted of groups of 12 to 40 animals. The minimum number suggested for direct release is 20.

From 1955 to 2000, over 1,200 bighorn sheep were transplanted within Arizona, and bighorn populations increased from 2,500 to over 6,000 during that time.  Notable reintroductions occurred at Aravaipa and Paria canyons and Goat Mountain, all of which support viable populations of bighorn sheep today.

The first successful translocation of sheep from Kofa was in 1957 when 4 bighorn were released at the Black Gap Wildlife Management Area in west Texas.  Through 2006, a total of 569 sheep have been translocated from the refuge.  Transplants of sheep from the Kofa were conducted nearly every year from 1979 through 1998 with no apparent decline in the population.  The 1996 Kofa National Wildlife Refuge & Wilderness and New Water Mountains Wilderness Interagency Management Plan and Environmental Assessment listed the following factors for consideration in transplanting sheep:

            1) estimated population and trends
            2) minimum estimated population of 120 in the New Waters
            3) minimum estimated population of 800 on the refuge
            4) herd demographics (minimum of 50% ewes, 14 lambs:100 ewes)

These factors are always considered but are not binding in determining whether a transplant will take place.  No transplants were conducted in 1991, 1996, 1997, 1999, 2000, 2003, or 2004 because of drought conditions or population estimates below 800.  In 2005, 31 sheep were transplanted from the Kofa.  Even though the 2003 population estimate was 623, it was thought that the population was on an upward trend and would recover quickly after the abundant 2005 rainfall and resulting improvement in habitat conditions.  While not the ultimate cause of the population decline, the 2005 transplant may have contributed to the low numbers seen in the Castle Dome Mountains on the 2006 survey. 

There continues to be a high demand for sheep of the mexicana subspecies to repopulate extirpated or dwindling populations in southern and central Arizona and New Mexico.  The Kofa NWR population is the most likely source for these transplants.  Sheep numbers on the Kofa are at historically low levels; therefore no transplants are currently being considered.  Transplant efforts will continue when population numbers approach the long-tem average (1981-2000) of 800.