Past Life: An unlucky Storm Petrel

From Shetland Life, October 1986, No.72

by Bob Furness

Having visited Foula every year since 1971 to ring and study seabirds, I was recently quite surprised to receive a computer printed letter notifying me that one of the birds I had ringed during my one and only visit to the Summer Isles off Ullapool had been recovered by a visitor to Foula. The bird was a storm petrel, a species that is rarely found dead.

Each bird that is ringed is given a metal ring with a unique number stamped onto it, and the instructions “Inform British Museum, London SW7”. The ringer has to fill out schedules which give the date and place of ringing, the age, sex and species of the bird. These records are stored until a ringed bird is reported via the British Museum, and then the ringing and finding details are entered onto computer and the printouts are sent to the ringer and finder. My printout explained that the storm petrel adult I ringed in May 1981 on Priest Islands, Summer Isles, had been recovered on Foula in early August. The ring and some remains of the petrel had been teased out of a pellet of indigestible material that had been regurgitated by a bonxie.

Although storm petrels are only about the size of a sparrow, like most other seabirds they are very long-lived. Storm petrels only start to breed when they are about five years old, and many may survive to breed for ten or 20 years. Our ringing in Foula has produced a few recoveries of storm petrels in winter. They all go to the seas off southern Africa, where one or two may be recovered dead on the beach each year. During summer, recoveries of dead storm petrels are very rare, although ringers often catch each other’s stormies in nets set at colonies. We know that most of those movements involve young birds, from two to five years old, that visit many different colonies before they choose where to breed. These prospecting “wanderers” may be caught one night on Foula, and the very next night on Fair Isle, Mousa, Yell or even as far away as Orkney or the Hebrides.

Stormies only visit their colonies during the hours of darkness to avoid being attacked by gulls or skuas, but our bird must have been caught despite this strategy. In fact, bonxies eat quite large numbers of stormies. I have often found their remains in bonxie pellets, though I have yet to find a ring on any of them. As bonxies are generally inactive at night I presume that they sometimes manage to catch stormies at sea during the daytime. The only ring I have ever found in a bonxie pellet was one which had been put on a tirrick chick at a colony in Finland 28 days earlier. It came as a surprise to discover that some of the tirrick chicks in Shetland in the late summer come from as far afield as Finland, and I had to feel sorry for this chick which had flown so far just to become a meal for a bonxie.

Storm petrels breed as far north as northwest Norway. There they find continuous daylight in mid-summer and to reduce the risk of being eaten by predators they don’t visit their Norwegian colonies until after the continuous daylight period is over. As a result, they lay their single egg several months later than our Shetland stormies, and the chicks don’t leave their burrows until about Christmas time, when it is continuously dark and they often have to dig through fresh snow to set off on migration to their winter holiday off southern Africa.

Because of their nocturnal habits and small size which allows them to nest in inaccessible crevices and burrows, we know less about the biology of storm petrels than we do about most other seabirds, but clearly they live interesting and eventful lives, and are remarkably well adapted to survive the difficult conditions that must face such small seabirds.