Audubon magazine has a fascinating story by Sami Emory about how an area of Germany is being overrun by feral rheas: “Inside Germany’s Giant, Hungry, Flightless-Bird Problem”. It seems remarkable but I suppose not really more than feral hogs or goats.
The rhea’s unlikely appearance in the wild in this corner of the world began two decades ago, when seven birds escaped from their enclosure on a private property. Eventually, the escapees settled in the state of Mecklenburg-Western Pomerania, primarily inhabiting the meadows, marshes, and cultivated fields of the 120-square-mile Schaalsee UNESCO Biosphere Reserve. The rheas thrived, and their numbers quickly climbed to dozens, and then hundreds.
The massive birds gained a foothold at a time when Europeans are wrestling with rising human-wildlife conflicts as megafauna rebound on the landscape, from resurging wolf populations to a new free-roaming bison herd. Like those animals, the rheas of Germany have become a matter of great interest and contention. Some see them as a welcome addition—a boon for conservation of a bird threatened elsewhere. Others argue that rheas are yet another destructive, human-introduced mistake, like the Burmese pythons that have overrun the Everglades or the European rabbits that have eaten their way across Australia, wreaking havoc on crops and spurring the decline of native plants and animals. As the rhea population has increased, so have troubles with local farmers, whose crops have become a staple in the ratites’ diet, as well as concerns that they could become an ecological burden.
This is part of anthropogenic changes to habitat worldwide. We’ve eliminated predators and set up systems that bring fast-reproducing animals to new geographic areas. As the story notes, rheas in Germany are less fearful and cautious than those in South America.
Ecologically, they seem to be operating somewhat like wild turkeys in the U.S. The extent to which they eat insect pests is helpful. Turkey populations in North America have spread widely beyond their nineteenth-century range. They reproduce fast and they flourish in the mixed cropland-secondary woodland environments that people have created. Most important, humans have cut down on natural predators of adult turkeys, although plenty of wild predators of eggs and chicks remain abundant.
The German rheas seem to be causing more crop damage, especially because they will eat young rapeseed plants from farmed fields. I find it fascinating to read about the legal situation in Germany, which will protect the rhea population because it has survived for several generations. The process of weighing the effects of the rheas and deciding how to control them is an intricate problem.