Responses of birds, rodents, and vegetation to livestock exclosure in a semidesert grassland site

Exclude grazers from semi-natural habitats

A controlled study in 1981-1983 at a semi-desert grassland site in Arizona, USA (Bock et al. 1984), found that bird communities differed between an area from which cattle had been excluded since 1968 and one that had been continuously grazed. Total bird numbers were higher on grazed plots than ungrazed in summer, with no difference in winter (summer: 193 birds counted in ungrazed sites vs. 270 in grazed; winter: 242 birds in grazed vs. 247 in ungrazed). Open-ground foraging species were significantly more abundant in the grazed area, whilst species that prefer grass and shrub cover were the most abundant birds in protected sites, but absent on grazed pasture. The authors argue that the bird communities prevalent in grazed areas were more typical of lower elevations and dry habitats, and may be an indication of desertification of intensively grazed semi-desert and plains grasslands.

Reduce intensity of grazing by domestic livestock

A site comparison study in 1981–1983 on a grassland ranch in Arizona, USA (Bock et al. 1984) found that reducing grazing intensity by excluding livestock increased rodent abundance. More rodents were caught in an ungrazed area (428 individuals) than in a grazed area (328 individuals). This was the case for hispid pocket mouse Perognathus hispidus (38 vs 16 individuals), western harvest mouse Reithrodonromys megalotis (26 vs 4), white-footed mouse Peromyscus leucopus (45 vs 24), southern grasshopper mouse Onychomys torridus (42 vs 8) and hispid cotton rat Sigmodon hispidus (118 vs 49). Merriam’s kangaroo rat Dipodomys merriami was less abundant in the ungrazed than the grazed area (5 vs 92 individuals). Silky pocket mouse Perognathus flavus abundance did not differ significantly between ungrazed and grazed areas (8 vs 5 individuals) and nor did deer mouse Peromyscus manicularus abundance (146 vs 130). Livestock were fenced out of part of a 300-ha study area from 1968 onwards. The grazed part was stocked with approximately one cow/10 ha. Rodents were live-trapped, from two hours before sunset to two hours after sunrise, on 71 occasions, from July 1981 to January 1983.

(Summarised by: Nick Littlewood)