Field mice may not carry passports, and nobody ever asked a tree frog for a green card, but do animals care about imaginary lines on a map? In fact, national borders can become natural borders over time, with significant consequences for the nonhumans living on either side.
After Israel normalized relations with its neighbor Jordan in 1994, University of Haifa biologist Uri Shanas studied how the fauna on either side of the border differed. He found that rodents in Israel were much more cautious than their counterparts in Jordan -- a distinction Shanas attributes to Israel's more modern agricultural development.
Such differences can persist for decades. Scientists have observed that red deer in the forests on the Czech-German border are still stuck in the Cold War, avoiding the old boundary because a long-dismantled electric fence once ran along it. But the effect isn't always negative. The 390-square-mile demilitarized zone between North and South Korea has been a no-go area for humans for decades, which makes it a great place for rare red-crowned cranes and Chinese water deer. Now there is talk of making the de facto wildlife preserve permanent: a very rare case of animals benefiting from human conflict.
Border: Largely fenced
Animals affected: Gerbils and red foxes
Border: Open and unfenced since 1989
Animals affected: Red deer
Border: Nearly a third fenced
Animals affected: Jaguars and ocelots
North Korea/South Korea
Border: Patrolled on both sides by nearly 2 million troops
Animals affected: Red-crowned cranes, Chinese water deer, spotted seals, and lynx, among others
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