Gruiformes are mostly ground-living birds, nesting in grasslands, marshes, and forests. On the ground, they are vulnerable to predators. Stoats introduced from Britain to New Zealand in the 1800s nearly wiped out the native takahe (Notornis mantelli). Impacts to grasslands, such as mechanical hay harvest, also destroy nests. European colonization of the U.S. was a disaster for whooping cranes (Grus americana). Hunting and agriculture reduced a thriving population of more than 10,000 to only 15 cranes. Conservation actions such as captive rearing have helped many gruiformes. The whooping crane population has increased to several hundred individuals, thanks to clever ideas such as using ultralight planes to teach migration routes to young birds. However, crane populations continue to be threatened by collisions with power lines, shooting, and predators. Several other crane species are listed on the "IUCN Red List of Threatened Species". Cranes are a symbol of good luck in Asian countries, but may need some good luck themselves to survive in the future.