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Providing evidence to improve practice

Individual study: Protective fencing against livestock and human disturbance increases abundance and species richness of birds

Published source details

Brooks M. (1999) Effects of protective fencing on birds, lizards, and black-tailed hares in the western Mojave Desert. Environmental Management, 23, 387-400

This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Exclude grazers from semi-natural habitats Bird Conservation

A replicated study in 1994-1995 in the Mojave Desert, California, USA (Brooks 1999), found that bird abundance and species richness were higher inside two 2.25 ha sites protected from sheep grazing and off-highway vehicles (OHV) since 1978, compared to adjacent sites that were grazed and driven over by OHVs. Significant differences were observed for sage sparrow Amphispizia belli, Le Conte’s thrasher Toxostoma lecontei, loggerhead shrike Lanius ludovicianus, verdin Auriparus flaviceps and ash-throated flycatcher Myiarchus cinerascens.  The authors suggest the increased abundance of bird species within the protected area is linked to a greater food supply.


Other biodiversity: Exclude grazers Mediterranean Farmland

A replicated site comparison in 1994–1996 in a desert site in south-central California, USA, found more birds and bird species in plots with grazers excluded, compared to sheep-grazed plots. Fewer black-tailed hares Lepus californicus, but more lizards were found in fenced plots, compared to unfenced plots. Perennial plant cover was higher in fenced plots, compared to unfenced plots. Birds: More bird species were observed nesting in fenced plots, compared to unfenced plots (3 vs 1 species). More birds and bird species were found in fenced plots (0.9–3.1 vs 0.7–2.6 species/survey; 1–11 vs 1–9 birds/survey), and six of 22 species were more abundant in fenced plots. Mammals: Fewer black-tailed hares were found in fenced plots (0–1.5 vs 1–4 hares/survey; 11 vs 22–31 droppings/m2). Plants: There were no differences in species diversity of perennial plants in fenced or unfenced plots (data reported as Shannon-Weiner indices). Perennial plant cover was higher in fenced plots (13–14% vs 6–7% cover). There were no differences in diversity of height, cover, or volume of perennial plants between fenced and unfenced sites (data reported as Shannon-Weiner indices). Reptiles: Fewer lizards were found in ungrazed plots, compared to grazed plots (1–4 vs 2–10 lizards/survey), and two of six species were less abundant in ungrazed plots, in some comparisons. Methods: Two 2.25 ha plots that were fenced in 1980 were compared to two plots that were grazed by sheep until 1994. Sites were matched for environmental variables. Birds were counted using 16 point counts in each plot, four times during breeding seasons (1994–1995) and twice during winter (December 1994, January 1996). Lizards were surveyed using 1.25 km transects three times in summer (1994–1995). Hares numbers were estimated with four 1.25 km transects and in sixty 40 x 50 cm sampling units in each plot. Plants were surveyed at 16 points in each plot in June 1995. Unfenced plots were also driven over by off-highway vehicles.