One of 15 Darwin’s rheas emerges from its holding pen during its translocation from Argentina to Chile. The large flightless birds are being moved as part of a programme to rewild degraded areas of southern American grasslands. “If we want to reverse the mass extinction crisis, international cooperation is going to be essential,” said a project leader. “Nature knows no borders” Photograph: Rewilding Chile/AFP/Getty Images A bumblebee pollinates a cherry blossom tree in central London as spring begins in the UK Photograph: Vuk Valcic/Zuma Press Wire/Rex/Shutterstock A sick sea lion with possible domoic acid poisoning is rescued by volunteers in