Boxing clever to save St Kilda petrels

Petrel nest on St Kilda. Picture: National Trust for Scotland
Petrel nest on St Kilda. Picture: National Trust for Scotland
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IT’S not a bird-box as we know it but it has produced a world first.

Craftsmen have built a designer home for the storm petrel, one of Scotland’s rarest seabirds, in an attempt to ­reverse a serious decline in population.

Now conservationists are celebrating the birth of the first chick in the man-made nest-boxes, giving hope for the future of the species on the remote island of St Kilda. Scientists can now monitor the breeding cycle of the birds to see what factors are having an impact on their long-term ­survival.

The St Kilda colony of the storm petrel is of major importance as it represents 94 per cent of the total European population. However, repeat surveys show a decline of more than half in seven years, from 27,700 to 14,500, with no clear explanation as yet.

Gina Prior, the seabird Ranger for the island’s owner, the National Trust for Scotland, said: “The cause of the decline is not clear though some research suggests predation by great skuas is implicated. Other factors may ­include reduced adult survival or a reduction in breeding success but very little information is currently available about these factors.”

The problem for scientists is that the storm petrel builds its nests in rock crevices or ­burrows into the ground. “Studying Leach’s storm ­petrels during the breeding season is extremely difficult,” Prior said. “Birds build their nests in natural crevices under boulders, at the base of stone structures such as cleits or in burrows dug into grassy slopes.

“The entrances to burrows are indistinct and difficult to see. Once a burrow is located it is rare that the nest chamber is visible from the entrance. The only method available to allow easy and repeatable access to nests is by providing artificial nest chambers.”

Previous versions of artificial chambers have not been successful in producing chicks but this year a new design has been developed in collaboration with Inverness College. The new design, fitted inside a rock surround, more closely resembles the cramped and secure nesting sites that petrels would use in the wild to afford a degree of protection from weather and predators. A perspex lid has been fitted so monitoring can be carried out without disturbing the birds.

“Results from this study provide a clear and immediate indication that the newly ­designed nest boxes were attractive to Leach’s storm petrels.” Prior said. “That a chick successfully fledged was an unexpected result. With nest boxes installed it is possible to track laying and incubation, record the attendance patterns of parent birds, monitor the growth rates of chicks, estimate breeding success and investigate whether breeding phenology changes over time.”

“If occupancy of the nest boxes improves then they offer the first real opportunity to improve our understanding of the breeding biology and behaviour of the Leach’s storm petrel at St Kilda.”

Scottish Natural Heritage’s Western Isles Manager, Susan Bain, added: “This is very exciting. When the petrels come ashore to breed you never see them. This is a major development, the first in the world.”

The new nest chambers were made in workshops at Inverness College by first year Modern Apprenticeship students studying woodwork as part of the Carpentry and Construction course.

Prior said: “Their involvement was greatly appreciated and mutually beneficial. The boxes were quickly constructed and donated to St Kilda, saving NTS staff time and resources, and the task provided the students with valuable experience of a ‘real’ world conservation project.”

The St Kilda archipelago, lying 41 miles west of the Isle of Benbecula, was famously abandoned in 1930 at the ­request of the remaining 36 islanders when life on the edge of Britain in the Atlantic ­became unsustainable.

The islands were bequeathed to the NTS in 1957 and allocated World Heritage status by UNESCO in 1986 in recognition of their natural heritage, exceptional natural beauty and for the significant natural habitats that it ­supports.

Night hunters: Storm petrel facts

n The rare Leach’s Storm Petrel is a small bird with a maximum body length of just 21cm and a wingspan of 43-48cm. It has a dark plumage and a white rump.

n Outwith breeding time the bird stays far out at sea, but likes to set up its nest in remote areas where it can conceal its chicks in rock crevices or in ground burrows.

n When they breed they lay a single white egg and become nocturnal hunters, allowing them to protect their nests from predators such as gulls or skuas during the day.

n Storm petrels mainly feed on sea plankton and lantern fish, which may only be found at night near the ocean surface.

n They have a life span averaging 20 years – long for birds – as storm petrels have a genetic mutation that protects their chromosomes from the effects of ageing.

n The largest colony of the small bird has been found on Canada’s Baccalieu Island.

Amanda Crawford