Sympatric cattle grazing and desert bighorn sheep foraging

Abstract

Foraging behavior affects animal fitness and is largely dictated by the resources available to an animal. Understanding factors that affect forage resources is important for conservation and management of wildlife. Cattle sympatry is proposed to limit desert bighorn population performance, but few studies have quantified the effect of cattle foraging on bighorn forage resources or foraging behavior by desert bighorn. We estimated forage biomass for desert bighorn sheep in 2 mountain ranges: the cattle‐grazed Caballo Mountains and the ungrazed San Andres Mountains, New Mexico. We recorded foraging bout efficiency of adult females by recording feeding time/step while foraging, and activity budgets of 3 age‐sex classes (i.e., adult males, adult females, yearlings). We also estimated forage biomass at sites where bighorn were observed foraging. We expected lower forage biomass in the cattle‐grazed Caballo range than in the ungrazed San Andres range and lower biomass at cattle‐accessible versus inaccessible areas within the Caballo range. We predicted bighorn would be less efficient foragers in the Caballo range. Groundcover forage biomass was low in both ranges throughout the study (Jun 2012–Nov 2013). Browse biomass, however, was 4.7 times lower in the Caballo range versus the San Andres range. Bighorn in the Caballo range exhibited greater overall daily travel time, presumably to locate areas of higher forage abundance. By selecting areas with greater forage abundance, adult females in the Caballo range exhibited foraging bout efficiency similar to their San Andres counterparts but lower overall daily browsing time. We did not find a significant reduction in forage biomass at cattle‐accessible areas in the Caballo range. Only the most rugged areas in the Caballo range had abundant forage, potentially a result of intensive historical livestock use in less rugged areas. Forage conditions in the Caballo range apparently force bighorn to increase foraging effort by feeding only in areas where adequate forage remains. © 2015 The Wildlife Society.

Determining Timing of Births and Habitat Selection to Identify Lambing Period Habitat for Bighorn Sheep

“…Domestic sheep and goats can transmit diseases to bighorn sheep (McClintock and White, 2007;Wehausen et al, 2011;Besser et al, 2012), and these issues are critical for the conservation and management of bighorn sheep populations (Cahn et al, 2011;Carpenter et al, 2014;O'Brien et al, 2014). Additionally, domestic cattle can affect habitat use by bighorns (Garrison et al, 2016). With female bighorn sheep showing general fidelity to birth sites and habitat for nursery groups (Etchberger and Krausman, 1999;Whiting et al, 2012), our data can be used to guide land-management decisions when assessing domestic livestock grazing allotments on public land, and when working with land owners on private land, which will help minimize conflict between these domestic and native ungulates.…”