Scientists have long known that isolation with fatal fences is a killer of nature.

Organisms must be connected to others of their species – to maintain viable populations.

Such connectivity allows animal species to limit inbreeding, maintain genetic diversity, withstand random demographic fluctuations, and recolonize areas from which they have gone locally extinct.

Many species also rely on annual migrations – for example, to move between distant wintering and breeding areas.

Photo credit: Alert Conservation

Finally, for many millions of years, species have moved in response to climate change, such as the Ice Ages, shifting to higher or lower latitudes or elevations.  “Move or die” has seemingly been their motto (although a few species could adapt rapidly enough to survive changing climates).

But despite the undisputed importance of movement and population connectivity, habitat fragmentation is continuing apace throughout the world.

And many of the world’s great animal migrations have collapsed or are rapidly declining.

Photo credit: Alert Conservation


Among the usual suspects in fragmenting our planet – habitat destruction, roads, sprawling urban areas, to name a few – is an old nemesis that many had underestimated.

Scientists are increasingly seeing fences as a big problem, especially for many large mammals, flightless birds, and low-flying species that fail to see fences in their path.

According to Alert Conservation, researcher Penny van Oosterzee reported recently that Africa once supported 14 major large-mammal migrations, but five have failed completely and the remainder all are in trouble.


Fences are a big part of the problem.  For example, Botswana, a Spain-sized nation in southern Africa, today has over 5,000 kilometers of fences just for cattle ranching.

Those fences don’t just stop cattle – they also halt big mammals such as Wildebeest, Hartebeest, and Zebras.

The fences become especially problematic, according to van Oosterzee, when droughts hit and the wildlife would normally migrate to wetter areas.  Following droughts, even quick surveys have revealed hundreds of thousands of dead animals along the fences.

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As their prey have declined, predators such as Lions, Leopards, Cheetahs, Hyenas, and African Wild Dogs have also suffered serious population losses.

And Africa is far from alone.  Elsewhere in the world – such as North America, Indochina, Borneo, Australia, and Central Asia – great wildlife migrations have collapsed or are dwindling dramatically.

The article was published on Alert Conservation. Continue reading. . .