Zebras in the Makgadikgadi region of Botswana have proven to be highly adaptable and have the flexibility to respond to significant environmental changes, a study exploring the effects of a 240km electrified fence has found.
Research conducted by Dr James Bradley as part of the Makgadikgadi Zebra Migration Research project indicates the fence, built in 2004 to keep wildlife and domestic stock apart, has benefited the 20,000 zebras of the Makgadikgadi, home to the world’s second-largest zebra migration.
The fence, which stands 2.4 metres high, was primarily built to protect livestock from lions in northern Botswana, where resources are scarce.
Bradley, 28, from the University of Bristol, in England, said his research was initiated as a follow-up study to the research of Dr Chris Brooks conducted between 2001 and 2005.
Bradley looked into the foraging behaviour, spatial distribution and adaptability to environmental changes of plains zebra (Equus quagga) in the Makgadikgadi.
Seasonal changes in resource availability were documented and GPS collars were used to record detailed movement data. Ongoing population dynamics were recorded throughout the study and the impact of the fence on the migratory zebra population was assessed where possible.
“The results of this study show that zebra are highly adaptable and have the flexibility to respond to significant environmental changes, yet they need to continue to be able to move freely within the Makgadikgadi,” he concluded.
“Initial results suggest that the Makgadikgadi fence has had a positive impact on the zebra population, but further monitoring is needed.”
Bradley said the Makgadikgadi region experienced significant unseasonal rainfall in June 2009, which had a major effect on the location of the zebra herds. In addition, the Boteti River started to flow again in 2009 after a 20-year hiatus, significantly changing water availability for wildlife and livestock.
That was followed by a large bush fire in September 2010 that removed nearly all of the available forage biomass, significantly influencing movement patterns and foraging behaviour.
There was also above average rainfall from 2008 to 2011 which led to increased forage growth across the Makgadikgadi when compared to the pre-fence study period.
“When [the] large bush fire passed through the Makgadikgadi in early September 2010, environmental conditions changed overnight, yet zebras were able to adapt their behaviour to minimise the impact of the fire. They were required to extend their drinking interval, travel further and work harder to meet nutritional requirements.
“All of the collared zebras followed a similar post-fire strategy suggesting that zebras have learnt to be highly adaptive to the challenges faced within the semi-arid Makgadikgadi.
“Yet, despite the foraging restrictions caused by the fire, zebras were not required to push their physiological limits as much as was necessary during the long dry seasons of 2002 and 2003.”
Bradley noted that during Brooks’ pre-fence study, zebras were recorded pushing their physiological limits; drinking on average every four days and foraging up to 35km from the Boteti riverbed.
“It was hypothesised that the construction of the Makgadikgadi fence and removal of livestock would influence zebra movement and foraging behaviour.
“The current study found that zebras decreased their drinking interval to every 2-3 days but with occasional longer intervals of 4-5 days.
“However, while zebras foraged within 5km of the riverbed, something they did not do prior to the fence being constructed, they continued to select forage areas that were 15-20km from the Boteti River.
“Before the fence was built, zebras were reliant on natural water seeps and two pumped waterholes in the riverbed for drinking water.
“However, these waterholes were also used by livestock and so competition for water was high. Following the erection of the fence and the consequent exclusion of farmers and livestock, zebras freely enter the riverbed throughout the day, even stopping to rest in the riverbed; something that did not happen pre-fence.
“The return of the Boteti River has provided abundant fresh water, resulting in zebras spending less than 0.5% of their time within 100m of the riverbed compared with nearly 5% of their time during the pre-fence study.
“Furthermore, while zebras are still vulnerable to predation around the riverbed, surplus killing is no longer evident. However, the observed changes cannot be attributed solely to the fence as forage and water availability were significantly different between the pre- and post-fence studies.”
Bradley noted that the fence was designed to be a physical barrier to separate wildlife and livestock yet, in its current state, it is highly permeable.
“Over time, multiple crossing points through the fence have been established by elephants which have allowed unrestricted access to the Boteti River. These crossing points have subsequently allowed cattle and donkeys to enter the [region] once more.”
“The fence appears to have had a positive effect on the behaviour of zebras. With this in mind, it is to be hoped that the fence can be modified and rebuilt in accordance with the Makgadikgadi Management Plan recommendations.
You can learn more about the Makgadikgadi Zebra Migration Research project here.