How are people affecting the distribution of less migratory wildlife in the southern Kalahari of Botswana? A spatial analysis

1. What they did

Since the 1950s, boreholes have opened the Kalahari to year-round cattle grazing, and wildlife numbers have fallen in many areas. Earlier work suggested that some less migratory wildlife avoid areas near people. The authors tested two possible reasons: (1) livestock changing the habitat, and (2) people hunting and poaching wildlife.

In the south-western Kalahari of Botswana, they compared four kinds of data against distance from the nearest livestock waterpoint:

• Spoor counts (September 1991). At 43 points, they walked a 100 m transect at right angles to a vehicle track, starting 50 m from the track, and counted wildlife and livestock tracks and dung. Wildlife counts were turned into a density score from 0 (not present) to 5 (very high, over 20); livestock spoor was often too dense to count and was scored directly on the same scale.
• Vegetation surveys in 20 x 50 m plots at the same points, estimating the cover of trees and shrubs, dwarf shrubs, grasses and bare ground.
• Ground counts. Sixteen counts from a vehicle driving at 40 km per hour between Tsabong and Gemsbok National Park (April 1991 to April 1992), giving the mean number of each species seen per 5 km.
• Aerial surveys. The average of six aerial counts from 1989 to 1993.

They mapped everything in a Geographic Information System (GIS) and used spatial statistics to allow for the fact that nearby points are not independent.

2. What they found

Livestock and vegetation

• Close to waterpoints, grass cover was low (about 15%) and woody plants had spread (bush encroachment). Grass cover rose to about 45% further away.
• Cattle spoor and cattle counts fell sharply with distance. Cattle were not seen beyond 13 km, though some cattle tracks were found up to 20 km. Goats and sheep stayed closer to water than cattle.
• The authors describe four zones: 0–1 km, very high impact, often bare ground; 1–5 km, high impact, low grass and bush encroachment; 5–10 km, low impact; 10–20 km, only occasional traces of cattle. The national park and the wildlife management areas showed no livestock effects; most effects were along the border with South Africa.

Wildlife

• Gemsbok were the clear exception. Their spoor and road counts rose steadily with distance from water, out to about 45–50 km, and they were likely very rare within 20 km. They were scarcer at 20–40 km than beyond 40 km, well past the zone where livestock change the vegetation. Only two gemsbok were seen inside the livestock impact zone in the aerial surveys. Trend-surface analysis and kriging of the aerial counts confirmed the same gradual gradient, which was hard to see by eye on the density maps.
• Steenbok and duiker spoor was slightly lower within about 8 km of waterpoints, but high densities still occurred well inside the zone of high livestock impact.
• Springbok were often common near waterpoints, apparently drawn to the shorter grass there, but also chose pans that have nothing to do with waterpoints.
• Springhare and scrub hare showed no link with distance to water.
• Kudu were too few to analyse.

3. What they concluded

• Habitat change caused by livestock appears to have little effect on most of these less migratory species.
• The gap between the livestock zone and high gemsbok densities points to hunting pressure, not competition with livestock, as the cause. The authors link this to a preference for gemsbok meat, hunting with horses, dogs and spears, and poaching. Many subsistence hunters said that hunting steenbok and duiker still takes more effort per kilogram of meat than hunting gemsbok.
• Springbok gathering in the same patches all year could make them easy to over-hunt.
• Overall, people using wildlife (hunting) matters more for the current distribution of common game in the southern Kalahari than animals avoiding areas changed by livestock.
• Aerial surveys combined with spoor data, waterpoint and vegetation surveys, and to a lesser extent ground counts, are useful for mapping species distributions in the Kalahari.

4. How tracking was or was not used

Spoor (tracks and dung) counts were one of the main data sources. Wildlife and livestock tracks and dung were counted along 100 m transects at 43 points and turned into density scores. Tracks and dung were identified with a reference collection the team gathered by following herds and identifying fresh tracks and dung, with Liebenberg’s (1990) field guide to the animal tracks of southern Africa as an extra reference. Steenbok and duiker spoor were combined rather than told apart. No trailing of individual animals is reported.

5. Tracker or observer certification

Not reported. The paper does not say who identified the spoor or how skilled they were. The acknowledgements thank field assistants Baipidi Pelekekae and Selefo Sabone, “especially with spoor identification”. The findings for gemsbok, steenbok and duiker rest partly on these identifications.

6. Other technologies, skills or innovations

• Global Positioning System (GPS) readings for every sampling point and every 5 km of the ground counts.
• IDRISI Geographic Information System (GIS) to measure each point’s distance from the nearest livestock waterpoint and to overlay impact zones on animal density maps.
• Aerial surveys from a Cessna 206, with counting strips about 200 m wide marked by rods and streamers on the wing struts.
• Trend-surface analysis and kriging to bring out a gradual pattern that could not be seen on the raw density maps.

7. Implications for conservation (from the paper)

• Hunting and poaching, rather than livestock grazing, appear to be the main reason gemsbok are scarce far beyond the livestock areas.
• Special game licence quotas are now supposed to be included in each hunting area’s total gemsbok quota.
• Springbok, concentrated in the same patches all year, could easily be depleted by hunting.