Invasive species blamed for extinctions

Scientists say invasive species are responsible for the majority of plant and animal extinctions and cost the world hundreds of billions dollars a year. The UN Convention on Biodiversity said they destroy forests and crops, and cause pollution. The UN study says human activity is making the effects worse, and recommends tougher border controls. Also on the programme: teachers strike in South Korea; and classical music performed by dogs. (Photo: A grey squirrel sitting on a branch. CREDIT: BBC)