The Pollycrisis

London’s feral parakeets are an invasive species—but they are also beautiful, and David Wingrave takes the chance to linger on their nightly roost at Hither Green Cemetery before asking whether they should be here at all. As calls for culls grow—backed by fears of crop damage, disease, and pressure on native wildlife—he probes what we really know about the harm these birds cause. Along the way, he asks deeper questions: how we decide where an animal “belongs,” when (if ever) it becomes native, and why we are so uneasy about seeing bright green birds in London’s parks.

The fix O’Gorman endorses may sound drastic, but his precautionary principle is shared by invasion biology, the subdiscipline devoted to the study of species transplanted from their native ranges. There is a long history of organisms moved by humans, whether deliberately or inadvertently, wreaking total havoc upon their new homes. The brown tree snake, native to Indonesia, northern Australia, and Papua New Guinea, was accidentally introduced to Guam by the US military following World War II and promptly ate its way through ten of the island’s twelve endemic forest bird species. Similarly, Nile perch released into Lake Victoria by British colonial forces gulped down roughly two hundred species of homegrown cichlids, fish found nowhere else on Earth. Cane toads in Australia, Miconia trees on Hawaii and Tahiti, rats just about everywhere—the list goes on. And if biodiversity loss, however regrettable, seems like an abstraction in the scheme of things, know that human culture frequently suffers direct impoverishments because of invasives. Chestnut blight, discovered in the United States in 1904 after chestnut trees were imported from Japan, effectively deleted the American chestnut tree from the continent; its products were central to the diet and lifestyles of various indigenous peoples and communities across Appalachia. Phylloxera, an aphid relative, was imported to Europe on American grapevines during the second half of the nineteenth century. The subsequent infestation resulted in the destruction, by some estimates, of 90 percent of all European vineyards.