Storm Petrels

How the tiny storm petrel, not much bigger than a sparrow but with longer wings and weighing just over an ounce, can survive a lifetime spent wandering the stormy oceans of the world is one of life’s mysteries.

The fact that they do not land on the water makes the mystery even deeper, for as their Latin name (Hydrobates pelagicus - Oceanic water-walker) suggests, they fly thousands of miles pattering their tiny feet on the surface of the sea picking up tiny pieces of offal, fish oil, marine invertebrates and plankton.

The name petrel is derived from the fact that like St Peter in the Bible, they appear to walk on the water, and they are also revered by mariners who call them Mother Carey’s Chickens from Mater Cara, the Blessed Virgin Mary, as they believed they gave warning of stormy weather. Breton folklore holds them as the spirits of dead sea captains who mistreated their crews and were doomed to wander the oceans forever as a penance, or the souls of dead sailors from Davey Jones’s Locker.

These birds, the smallest oceanic seabirds in the world, breed on the Pembrokeshire islands, particularly Skokholm where they occupy small rock crevices and often stone walls, laying one egg and brooding one chick between April and July. They make landfall only at night because of their vulnerability to predators, their arch enemy being the Little Owl which frequents Skokholm and has the nasty habit of catching and beheading petrels and storing them in cracks and crevices for future consumption. Little Owls are strictly controlled on Skokholm during the petrel breeding season because of the toll they take on their favourite food.

Storm petrels range from Iceland down to the South African Cape and breed in Britain and Ireland, the Faroes, Biscay and the Mediterranean, 90% of them favouring the windy, plankton-rich seas round the Cape of Good Hope. The British population is estimated at 20,000 and they have a lifespan of about 20 years. Their flight is a constant, easy, relaxed wingbeat, rolling from side to side or turning and dropping to feed, swooping like swallows or bats over the surface, and their speed is deceiving for such a small bird. They have often been seen effortlessly overtaking ferries and other ships. Their call is a soft, purring trill with an abrupt ending and naturalists on Skokholm have learned to detect their nesting holes by listening for the distinctive sound. Their sharp sense of smell is said to enable them to detect oily fish, and small flocks gather to feed in the vicinity of ships which have stirred up the sea’s surface. Not surprisingly, because of their size, details of their life at sea is difficult to acquire but they are monogamous, keeping the same partner for life and also like to nest in colonies. They are extremely vulnerable to ground predators, so nest only on mammal-free islands where there are none, therefore the Pembrokeshire islands are ideal.

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