In the Edwards Plateau of Texas.
THE RE-ESTABLISHMENT OF THE COYOTE IN THE EDWARDS PLATEAU OF TEXAS
GARY LEE NUNLEY, U. S. Department of Agriculture, Animal and Plant Health Inspection Service, Texas Animal Damage Control Program, P.O. Box 100410, San Antonio, TX 78201-1710
Abstract In the early 1900s organized predator control was initiated to remove coyotes (Canis latrans) and wolves (C. lupus and C. rufus) from the sheep and goat producing areas of Texas. Operations were begun in the Edwards Plateau, the largest area of sheep concentration. By the 1920s, many of the inner Edwards Plateau counties were considered to be almost free of coyotes and wolves In the 1950s coyotes and wolves were extirpated from most of the Edwards Plateau. After a coyote population irruption in the early 1960s, coyotes began to re-establish themselves on the periphery of the Plateau. This encroachment process has accelerated in the 1990s and thus continues to expose more sheep and goats to predation by coyotes.
In the early 1900s, organized predator control was initiated to remove coyotes and wolves from the sheep and goat producing areas of Texas. Operations were begun in the Edwards Plateau, the largest area of sheep concentration. The Edwards Plateau and, to a lesser extent, portions of other adjoining ecological areas presently (1995) account for 19% (1.7 million head) of the sheep and 90% (1.95 million head) of the goats in the United States (USDA 1995) (Fig. 1). The Edwards Plateau itself encompasses about 24 million acres of “Hill Country” in west-central Texas, comprising all or portions of 37 counties (Fig. 2). By the 1920s, many of the interior Edwards Plateau counties were considered to be practically free of coyotes and wolves. Click on image to view content.
Factors responsible for coyote re-establishment
The range expansion of coyotes within the Edwards Plateau is directly related to the presence, viability, and geographical distribution of the sheep and goat industry. Gee et al. (1977) surveyed former sheep producers in Colorado, Texas, Utah, and Wyoming who had terminated sheep production. Factors which they rated of greatest importance in their decisions to discontinue sheep production were high predation losses, low lamb and wool prices, shortage of good hired labor, the sale of their land, and their own age. The sheep and goat industry is also now faced with the loss of the wool and mohair incentive program which will eliminate some additional producers.
A major factor for declining sheep and goat production on the eastern periphery of the Edwards Plateau has been the changing land use away from sheep and goat production. This occurs through the sale of properties due to economic pressures, especially near urban centers and recreational areas. It often follows that the new land managers or absentee landowners do not pasture sheep or goats. Further, they often do not engage in, or in many cases even allow, coyote control activities on their properties. Consequently, sheep and goat producers who border, or are surrounded by properties where coyote control is not conducted, bear the brunt of the coyote’s tendency to depredate sheep and goats. These producers on the fringe of the sheep and goat production area find that it especially difficult to control losses to predators on their ranges (Nunley 1995).
Predation losses due to the limitations and cost of the application of current predator control techniques have also contributed to the decline in the number of sheep and goats in Texas. The loss of toxicants in 1972 greatly reduced the efficiency and effectiveness of coyote control over large areas.
In their discussion of eradication or control for vertebrate pests, Bomford and O’Brien (1995) provided 6 criteria to determine whether eradication is preferred over continuing control. Since there was no end point to control, the historical events in the Edward Plateau do not meet their specific definition of eradication. However, the criteria are still important when attempting to extirpate coyotes from a given area, thus allowing control efforts to concentrate on the area’s periphery to prevent infiltration.
These essential criteria include (1) rate of removal exceeds rate of increase at all population densities, (2) immigration is prevented, (3) all reproductive animals must be at risk, (4) animals must be detected at low densities, (5) discounted benefit-cost analysis favors eradication over control and (6) suitable socio-political environment including access to private property. Bomford and O’Brien (1995) indicate that a negative in any 1 of the first 3 criteria will doom an eradication attempt; a negative in criteria 4-6 will greatly reduce the feasibility and desirability of eradication. Considering the difficulties in achieving all of these criteria, it is likely that the re-establishment of coyotes within the Edwards Plateau will continue.
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