Fences Elephants 2014 05 28
Even well-made and maintained fences may be broken by determined elephants as in this example from Kenya. Image: Lauren Evans.

They say good fences make good neighbours (at least if you ask Robert Frost), but things get thornier when it's wildlife rather than fellow humans on the other side of that fence. Over time, fences have morphed from simple wood or stone designs to the increasingly impenetrable metal and barbed-wire structures used today. These may (or may not, as these fence-demolishing elephants clearly prove) do a great job of containing grazing livestock and preventing wildlife from entering areas where humans don't want them ... but putting up fences can also have some unfortunate and unintended consequences.

A recent paper in the journal Science calls attention to this complex and tricky problem, recognising that people and wildlife are sometimes uneasy neighbours. Dr Rosie Woodroffe at the Institute of Zoology in London, with colleagues there and at the Wildlife Conservation Society in New York, points out that although fencing can have conservation benefits, it can cause a lot of damage too (the paper also contributes to a recent debate sparked by scientists arguing the costs and benefits of fencing for lion conservation).

For a start, fences can be a treacherous obstacle, as grisly photographic evidence of animal casualties, everything from garroted birds to ensnared deer and antelope, clearly shows. In the North American prairies, fencing collisions are suspected as one factor contributing to the decline of sage grouse. Fences can also separate mother deer from their fawns (a sight likely to break even the most hardened of human hearts).

Thanks to their habit of impaling prey on fences (or thorny tree branches), shrikes are sometimes called 'butcher birds'. Image: Billtacular, Flickr

And then there are those wily predators that have figured out how to use fences to their advantage. Wolves and African wild dogs, for example, have learned to chase prey into fences, while the loggerhead shrike, a North American bird of prey, often impales its quarry on barbed wire (a useful substitute for thorn bushes), stashing it there for later snacking, or decorating its strung-out victim to attract a mate. For predators of another kind – poachers – fencing can also provide a convenient supply of wire for constructing snares, Woodroffe and colleagues point out.  

Fences can also create barriers that carve up and sometimes diminish habitat for wildlife, decreasing the number of animals a landscape can support. In the 1950s, veterinary fences were constructed in Africa to prevent diseases from spreading between wild animals and livestock. Fence construction in Kruger National Park, for example, restricted wildebeest to half of their original range, obstructing their migration to seasonal water sources and contributing to a population drop of almost 88%. Similar scenarios have played out in other parts of the world too. In the North American prairies, fencing sometimes prevents pronghorn antelope from reaching high-quality habitat. Climate change adds an additional wrinkle to the problem – as the suitability of some habitats shifts, fences can stand in the way of animals seeking new ranges.

"In some parts of the world, fencing is part of the culture of wildlife conservation – it's assumed that all wildlife areas have to be fenced. But fencing profoundly alters ecosystems, and can cause some species to disappear,” Woodroffe warns.

“In some parts of the world, fencing is part of the culture of wildlife conservation. But fencing profoundly alters ecosystems, and can cause some species to disappear.”

But fences do have their pros. For endangered species like the Hawaiian silversword, a plant that belongs to the daisy family, fences are actually critical to survival. Without fenced enclosures to protect them, the tasty silverswords would be nibbled to nothing by munching ungulates like feral goats.

Clearly, the pros and cons of new and existing fences need careful consideration. Woodroffe's co-author Sarah Durant of the Zoological Society of London points out that there are plenty of fencing alternatives out there. When it comes to keeping trampling hooves away from crops (or hungry predators away from livestock), for example, better animal husbandry, community-based crop-guarding, insurance schemes and planning for wildlife-sensitive land use are all possible solutions for warding off conflicts between people and wildlife.

And throwing some creative thinking into the mix can bring novel solutions. If fencing is unavoidable, there are guidelines to make it more wildlife-friendly, such as partial or permeable fencing that allows management on a species-by-species basis. Rhino fences, for example, keep rhinos out but allow other animals to pass. 'Living' fences incorporate thorns or thick shrubbery, and using beehives along modified fences shows promise for keeping the peace between humans and crop-raiding elephants by exploiting the pachyderms' fear of the winged insects (though it's unclear whether this solution will work for elephants marauding at night, when bees are snoozing).

Enclosed by a boma's thorny fence, cattle and other livestock are protected from predators at night. Image: George Lamson, Flickr

But let's not rule out thinking inside the box. In Kenya and Tanzania, Maasai herders bring their grazing cattle and livestock into a boma or corral at night, where a thorn fence keeps the animals safe from predators, explains Durant. "You can produce more secure versions of that, that keep communities safe at more dangerous periods, such as at night," she explains. At a tenting campground in Canada's Lake Louise, for example, an electric fence runs along the perimeter, keeping the campers within safe from possible run-ins with grizzly bears.

Fences can play a role in conservation, but there are many downsides associated with their use on a large scale, Durant adds. "Animals need to be mobile to access resources," she explains, and fences prevent that. Increased awareness of this has created a trend towards removing fences instead of building more, such as partial removal of fencing between the Kruger National Park and Limpopo National Park in Mozambique.

Durant emphasises that conservation is not just about a single species. Fences that safeguard one species might harm another. Ultimately, she says, conservation of awe-inspiring wild animals requires much more money. "We should be thinking about increasing the budget for reserves, because they all run on very, very little money." It’s an issue, it seems, of dollars and fence.

Top header image: Ingrid Taylar, Flickr