Shocking reduction in Africa's elephant numbers

There has been a big reduction in Africa's elephant population, according to the first continent-wide aerial census.

Numbers have been cut by a third in the last decade, with at least 144,000 killed.

Botswana is home to more than 40% of the continent's elephants but, as our Africa correspondent Alastair Leithead reports, it is now being targeted by poachers.