| Between 1987 and 2001, pronghorn (Antilocapra americana) populations in Trans-Pecos, Texas have experienced a 70% decline. The causative factors associated with the decline are unknown, but appear to be related to drought. I evaluated the relationships between pronghorn population demographics (fawn production, buck:doe, population numbers) and precipitation (raw precipitation, Palmer Drought indices) for the Panhandle and Trans-Pecos districts of Texas from 1977-2004. In the Trans-Pecos, fawn production (range = 305-4,407) and population size (range = 5,061-17,266) showed high variability, whereas buck:doe (range = 1:0.48-1:0.69) remained stable. In the Panhandle, fawn production (range = 334-2,215), population size (range = 2,568-6,519), and buck:doe (1:0.31-1:0.62) remained stable. Precipitation in the Trans-Pecos was also highly variable, ranging from 18 to 57 cm. Precipitation in the Panhandle was more regular, ranging from 36 to 70 cm. In the Trans-Pecos, the relationship between fawn production and raw precipitation (R > 0.86, P < 0.001) suggested that fawn survival may be more closely related to immediate moisture conditions, whereas pronghorn population size was more influenced by long-term population trends. In the Panhandle, no correlation was found between pronghorn population demographics and precipitation. Management plans for pronghorn populations in more arid regions should include drought contingencies. |
