The Urban War on Invasive Species Cannot Be Won

Earlier this month, the city of Madrid announced that it would begin an “ethical” cull of up to 12,000 monk parakeets that had taken up residence in the Spanish capital. Native to South America, the chattersome, bright-green birds construct huge communal nests, often on utility poles, where they can cause fires and power outages. Their nests are so heavy that if they tumble to the ground, they risk injuring those below. The culling program—a combination of hunting with traps and egg sterilization—will cost €100,000.

A similar parakeet eradication campaign was waged in London earlier this decade; culls of rose-ringed parakeets, which are now common in much of Europe, are afoot in France. Meanwhile, in Berlin, it’s a North American transplant—the swamp crayfish—that is causing problems: Authorities announced this month that they had removed 22,000 of the crustaceans from the city’s many lakes this year, where they’d been seen as a threat to local fauna due to their extremely fast reproduction and lack of local predators.