Holy Island is a low rocky outcrop in the coastal mudflats connected twice daily by a causeway revealed by the tides. Arriving, straight away I could hear a low drone. I could not tell whether this was natural or the sound of many motors.
Initially I walked slowly along a long path until I crossed dunes to reach the sea. Then I hurried back and returned with my most powerful telescope. The constant gronking noise came from common seals resting on rocks just out to sea.
At first I was too distant to make out much more than their shapes.
Edging closer by rounding the shoreline, I began to make out the features on their flippers and faces.
I think these were mainly females with their pups. The moved contently, turning and twisting in the sun and slipping in and out of the sea.