In 2004, amid fears of bird flu, Europe banned the import of birds from Southeast Asia. Fourteen years later, Mexico declared monk parakeets, commonly kept as pets, an invasive species. These two events are directly linked, according to a study published in PLoS ONE and reported by Allie Wilkinson for Nature. The birds are agricultural pests and flocks can cause blackouts, writes Wilkinson.
How it happened: The ban (and a 2007 law expanding it to all countries) meant European demand for exotic birds declined. In 2008, Mexico banned the capture of native birds to protect wild populations. This shifted the monk parakeet market from Europe to Mexico, which imported over a half-million of the birds.
Why it matters: "This whole invasion seems like it was just a fascinating series of unforeseen consequences of regulation changes," study author Elizabeth Hobson told Nature. It shows how policies can have impacts an ocean away.