On a dark moonless night an eerie cackling can be heard across the island as 16,000 pairs of Manx shearwaters , 5 per cent of the British population , come ashore to lay and incubate their eggs in abandoned rabbit warrens or newly dug burrows .
On a dark moonless night an eerie cackling can be heard across the island as 7,000 pairs of Manx shearwaters , 3.5 per cent of the British population , come ashore to lay and incubate their eggs in abandoned rabbit warrens or newly dug burrows .