Using Artificial Passageways to Facilitate the Movement of Wildlife on Namibian Farmland

1. What they did

Wildlife-proof fences are spreading across southern Africa’s private farmland as wildlife farming grows. They keep valuable game in, but they also block free-ranging animals, and digging animals such as warthogs, porcupines and aardvarks keep breaking through underneath, which means daily patrols and repairs.

On a Namibian wildlife farm, the researchers tried a cheap fix:

• Installing the tyres. They set 49 discarded car tyres (40 cm radius, giving a 37 cm opening) into a 19.1 km wildlife-proof fence at ground level, at the places where warthog damage was worst. The tyres were anchored with short metal poles and wired to the fence. Tyres were on average 277 m apart.
• Watching one tyre. One tyre, between the wildlife reserve and a neighbouring cattle farm, was watched with a motion-triggered infrared trail camera for 96 trap days between August and December 2010. Cheetah, leopard and brown hyaena spoor had often been seen there on fence patrols. No bait was used. The camera stood 15 m from a captive cheetah holding facility.
• Checking spoor. An experienced San tracker checked the spoor at the monitored tyre and also recorded spoor of animals crossing through the other, unmonitored tyres. Spoor at the monitored tyre was erased after every visit.
• Counting costs. They compared the number of holes repaired per day along the fence before and after the tyres went in, and calculated what the tyres cost to install.

2. What they found

At the monitored tyre

• The camera made 100 independent records (photos of the same species at least 12 hours apart) of 11 mammal species passing through the tyre.
• Black-backed jackals used it most (44 records), then porcupines (21), cheetahs (9) and warthogs (7). Six of the 11 species were carnivores, and carnivores made up 62% of the independent records.
• The nine cheetah records were of at least seven known individuals: a collared coalition of three males (four times), a coalition of two uncollared males (three times), and an adult female with a subadult cub (once). One set of photos was overexposed and could not be identified. One male leopard was photographed four times. All were known residents of the area.
• Spoor showed one cheetah and two leopard crossings that the camera missed, probably during its 1 minute pause between triggers.
• Cheetahs passed only in the evening (19:00 to 21:00), around midnight and especially in the morning (07:00 to 09:00). The leopard passed at night and in the morning. Jackals used the tyre at all hours.
• It appeared that one pair of jackals made 27 of the 44 jackal records, although this was not measured.

At all 49 tyres

• Warthogs were seen using all 49 tyres.
• The San tracker identified spoor of 11 species at unmonitored tyres, including aardvark, honey badger, springhare, steenbok and Helmeted Guineafowl. Cheetah and leopard spoor was found at six of the 49 tyres.
• A springbok and a juvenile red hartebeest were seen passing through.
• Altogether, the tyres were used by at least 18 mammal species and three bird species. There was no sign of brown hyaenas at any tyre.

Costs and fence damage

• Holes needing repair fell from an average of 31.3 per day to 13.6 per day (10 days each), a significant drop.
• The whole programme cost USD 252, or USD 5.13 per tyre: 79% labour and 21% fuel. Tyres, poles and wire all came from scrap. Each tyre took about 1 hour to install.
• Daily patrols and repairs fell from 4 to 5 hours to under 2 hours, saving about USD 1.4 a day, so the installation paid for itself in about 180 days.

3. What they concluded

• Although their data are preliminary, discarded tyres gave an effective, cheap passageway for many wildlife species and eased one of the common harms of impermeable fences, at least for the species seen at their site.
• Repeat visits by known cheetahs and the leopard suggest that using the tyre was habitual, not chance. The high numbers at the monitored tyre were probably boosted by the captive cheetahs nearby, which may have drawn resident males.
• Collared cheetahs and leopards kept their existing home ranges despite the fence, crossing through the tyres. This may let predators reach prey on other properties and so ease predation pressure on fenced-in game.
• They found no evidence that predators used the tyres as prey traps. But tyres could let carnivores into areas holding very valuable game such as sable antelope; there, swing gates may be better.
• Different tyre sizes could allow some choice over which species can pass.

4. How tracking was or was not used

Tracks and signs identification was a key part of the study alongside the camera. An experienced San tracker did all the spoor assessments: confirming crossings at the monitored tyre, including three large carnivore crossings the camera missed, and identifying which species had crossed through the 48 unmonitored tyres. Most of the species list beyond the camera’s 11 species came from spoor. Spoor at the monitored tyre was erased after every visit so new crossings could be read. Spoor of cheetah, leopard and brown hyaena seen on earlier fence patrols guided where the camera was placed. No trailing was reported.

5. Tracker or observer certification

Reported but not validated. The paper describes “an experienced San tracker working for the carnivore research programme” but does not name them, give a certification or test their skill. Their spoor identifications account for several of the species recorded and for the extra cheetah and leopard crossings.

6. Other technologies, skills or innovations

• Discarded car tyres as fence passageways, built from scrap materials.
• An infrared, motion-triggered trail camera (Stealth Cam Rogue 5.0) set 48 cm above ground at an angle of 15 to 25 degrees to the tyre, to capture both flank and face of animals passing through. It took a photo every four seconds when triggered, with a 1 minute pause between bouts.
• Individual cheetahs and leopards identified from spot patterns and collars (some cheetahs carried GPS collars).

7. Implications for conservation (from the paper)

• Fences fragment habitats and populations, and very few techniques had been developed in Namibia to let chosen wildlife through or keep it out. Tyre passageways can restore some connectivity at very low cost.
• Tyres reduce fence damage and patrol time, which makes them attractive to landowners.
• Africa lacks the applied research on predator passages that has been done for cougars in North America, even though Namibia has six large carnivore species living alongside valuable wildlife and livestock.