Call sounds help Skomer's Manx shearwater census

Half the world's population of Manx shearwater are thought to be living on Skomer off Pembrokeshire.

Researchers have been holding a census of the seabird, which breeds on the island.

Last estimates put it at 300,000 pairs.

Results of the latest survey are now being analysed.

The health of the bird is seen as a good indicator of the state of the seas and marine environment around Wales.

Sarah Parmor, Skomer visitors' officer, explains how an MP3 recording of call of the adult shearwater is played down burrows to count whether there is a bird inside.