About the Authors
The Royal Society for the Protection of Birds, Edinburgh, United Kingdom
The Royal Society for the Protection of Birds, Sandy, Bedfordshire, United Kingdom
BirdLife International, Cambridge, United Kingdom
The authors have declared that no competing interests exist.
Conceived and designed the experiments: GMB PFD SHMB. Analyzed the data: GMB PFD. Contributed reagents/materials/analysis tools: GMB SHMB. Wrote the paper: GMB PFD SHMB.