Seabird defies decline at Scots island colony

A recent survey has found numbers of the European storm-petrel have more than doubled at an important Scottish colony in 12 years.

The findings from the Shetland island of Mousa have delighted experts who have witnessed widespread decreases in other seabird populations in recent years.

Mousa has nearly 40 per cent of the UK population of storm-petrels, making it the largest colony of the birds in the UK.

In 1996, just 5,400 pairs of storm-petrels were found on the island reserve, which has been designated a Special Protection Area (SPA) and Site of Special Scientific Interest (SSSI).

But research in 2008 by RSPB Scotland and Scottish Natural Heritage (SNH) - the results of which have just been published in a scientific journal - recorded an estimated 11,800 pairs.

Staff had to adopt an unusual method to record the birds, which are notoriously difficult to count due to their nocturnal and nesting habits. They often set up home in dry-stone walls and boulder beaches on Mousa, as well as in cavities in the Iron Age broch to which they return under the cover of darkness.

To monitor the population, researchers played a tape recording of a storm-petrel call into the potential nest sites and then counted every return call.

Storm-petrels are the smallest seabirds in the Atlantic, but they are very robust and can travel long distances for food.

It is this ability, and the fact they are not dependent on a single source of food, that has helped them recover.

Dr Mark Bolton, RSPB principal conservation scientist, said: "Despite being a similar size to a sparrow, storm-petrels are capable of flying hundreds of miles from the colony to search for food, and chicks can tolerate periods of several days without being fed by their parents.

"They feed on a wide variety of prey species, which makes them resilient to the declines in any one particular food type. The fortunes of many other seabird species are closely tied to sandeels, whose stocks have diminished in recent years".

Glen Tyler of SNH said another key to the birds' success is the lack of introduced ground predators on Mousa.

"Rats, mink and feral cats all prey on storm-petrels, and the presence of such predators has led to the disappearance of some colonies in the UK. It is essential that Mousa remains free of ground predators if we are to safeguard the long-term future of this species."

Storm-petrels have connections to maritime folklore. They are seen as a sign of bad weather, while their habit of following sailing boats made the species a source of legend for early sailors, who believed the birds were bodies of lost sailors or wicked sea captains.