Influence of range condition on density and diet of black-tailed jackrabbits and diet of cattle in southcentral New Mexico

A study was conducted near Las Cruces, in southcentral New Mexico, to determine the influence of range condition on jackrabbit (Lepus californicus) density and diet and cattle (Bos taurus) diet. Two range condition classes were selected for the study: (1) the fair condition (FC) range on BLM land, which contains about 25-50% climax vegetation, and (2) the good condition (GC) range on the College Ranch, which contains about 50-75% climax vegetation. Line transect procedures were used to estimate jackrabbit populations from July 1988 to December 1990. At the same time, vegetation cover and mean heights were determined using the line intercept procedure. Jackrabbit and cattle feces were analyzed seasonally from summer 1988 through spring 1990 by the micro-histological method.;Jackrabbit densities on the GC range differed (P = 0.056) from those on the FC range. I attributed this difference to the FC range containing more protection cover and preferred forage than GC range.;The GC range contained higher (P ;Range condition influenced the forb and shrub diets of jackrabbits, but not the grasses. On the GC range, jackrabbits consumed overall 22, 40, and 38% grasses, forbs and shrubs, respectively, and 22, 24, and 55% on the FC range. Cattle diets also were influenced by the range condition. Cattle consumed 60, 35, and 6% grasses, forbs and shrubs, respectively, on the GC range, and 57, 24, and 19%, respectively, on the FC range.;Comparative jackrabbit and cattle diets within each range condition revealed that overall jackrabbits consumed less grasses than cattle on a ratio of 1:3, both animal species ate a similar proportion of forbs; and jackrabbits ate more shrubs than cattle, resulting in moderate average dietary overlap of 41%. There was no detectable range condition influence on dietary overlap. On the average, poisonous plants comprised 12% of the total cattle diets on both range sites. Poisonous plants constituted 35% of the diet for jackrabbits. There was no range condition influence on the total amount of poisonous plants consumed by each animal species.