There is an error in the Funding statement. The correct number for Wellcome Trust is 095787/Z/11/Z to KH. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
- Mark-recapture survey
- Questionnaire survey