The Independent (London)
Species of seabirds in the Outer Hebrides are threatened with
extinction because of a biodiversity experiment to introduce hedgehogs
to the islands off the northern British coast, according to a study
published this week.
Numbers of ground-nesting birds, such as
dunlin, lapwing, redshank, and snipe, have fallen in recent years
because their eggs are being eaten by Erinaceus europaeus, the
European hedgehog.
A study published in the Journal of Applied Ecology showed that on the island of South Uist the chances of wading birds successfully nesting more than doubled in areas that were cleared of hedgehogs.
The discovery has important implications for several other Scottish islands where hedgehogs have been introduced in the belief that they are strict insectivores whose effect on the fauna is entirely benign.
For the study, conservationists created safety zones at Loch Bee and Drimore barring hedgehogs. The trials, on sandy ground considered ideal habitat for ground-nesting birds, were ringed by half-metre-high electrified wire. Hedgehogs were observed as they unsuccessfully tried to enter the protected zone, their tiny legs carrying them up to half a kilometer (third of a mile) in search of eggs.
The fence was breached in parts by burrowing rabbits, but it proved an effective deterrent to the hedgehogs' nocturnal forays, and showed the birds would thrive without the mammals' interference.
Hedgehogs were introduced to the Western Isles in 1974 and have since colonized areas on Benbecula and North Uist; they now number 5,000 in total. At the time it was considered a progressive project for the wildlife of the Western Isles whose only other native mammalian predator is the otter. Other attempts to boost the islands' biodiversity have seen the introduction several years ago of the brown rat and the polecat ferret, neither of which prey on birds' nests.
Conservationists, backed by the Royal Society for the Protection of Birds—which says that since the hedgehog introduction the dunlin population has been cut by 65 percent and the redshank's by 40 percent—acknowledge that moves to relocate the hedgehog have backfired. They are now calling for a wider purge.
The consequences for ground-nesting birds of the introduction of mammalian predators are well documented, particularly on islands. According to a study in 1984, such experiments have been the cause of about 42 percent of bird extinctions.
Legislation in Britain prohibits the introduction of species but does not place the same restrictions on animals native to one part of the country being moved outside their natural range.
The report's author, Digger Jackson, said: "The threat to biodiversity, particularly on the islands from the redistribution of native species within a country is generally overlooked…yet the biological consequences are potentially just as serious. Application of good ecological principles and practice is important…and ultimately that could make the difference between a species' survival and its extinction.
"The outcome of this work contrasts with the widely held perception that hedgehogs are harmless insectivores and, on many other Scottish islands where they've been naturalized for much longer, that they are a benign addition to the fauna."
