From time to time the wetlands of northern Xizang stage one of nature's most entertaining confrontations. When a stray sheep blunders into their domain, the normally graceful black-necked cranes transform into feathered enforcers, flapping, charging and screaming until the intruder beats a hasty retreat. By coincidence, their latest triumph takes place on May 22 – International Biodiversity Day. Their victory dance, a jubilant display of jumps and calls, proves that even the normally gentle cranes know how to celebrate a hard-won battle.