How to put an elephant to sleep

Fitting a tracker on a large elephant is a risky operation. First a vet has to find a safe place to dart it with anaesthetic, then the team has to work quickly attach the collar.

Elephants Without Borders is working with southern Africa governments to monitor and protect the animals that wander across Botswana, Namibia, Angola, Zambia and Zimbabwe.

The BBC's Alastair Leithead reports.