Why hedgehogs are not welcome in the Hebrides
The hedgehog is arguably one of Britain's favourite mammals and possibly our most threatened.
Since the 1940s hedgehog numbers have dropped from an estimated 30 million to fewer than one million and conservationists warn they could even be extinct in Britain by 2025.
But during the past decade hundreds of hedgehogs have been deliberately killed by official government bodies, at eye-watering costs to the taxpayer.
In the Western Isles of Scotland, the non-native hogs have a bad reputation. But are they really to blame for a decline in wading birds?
The story begins almost 40 years ago, in 1974, when some hedgehogs were released into a garden on the Hebridean island of South Uist, in order to help control slugs and snails.
Here, the hedgehogs faced few of the hazards that have so reduced numbers of their mainland cousins, such as heavy traffic on trunk roads and city streets, pesticides in gardens, or predation by badgers.
No wonder they soon multiplied and spread, and within a couple of decades had a population estimated at about 5,000 individuals.
By then they had also spread to the neighbouring islands of Benbecula and North Uist, which are connected to South Uist by causeways along which the hedgehogs were able to travel.
Every spring, the sandy soils along the western side of these islands are covered with a carpet of grasses wild flowers, known as 'machair'.
Machair is home to some of the densest breeding populations of wading birds anywhere in the world; with dunlin, ringed plover, oystercatcher and redshank filling the air with their calls throughout the spring and summer months. The numbers of these birds are so high that the islands are an internationally important site for them.
When the wader population on the islands began to drop rapidly, the invading hedgehogs were soon implicated in the decline: the wader nests provided easy pickings in the form of tasty eggs.
Almost 30 years after the hedgehogs were first introduced to the islands, an organisation called the Uist Wader Project was formed to launch a cull of the hedgehogs, in order to prevent the nesting waders being wiped out.
The project - a coalition between Scottish Natural Heritage, RSPB Scotland and the Scottish Government - did manage to cull about 700 hedgehogs, but this soon attracted criticism: partly because there were still so many hedgehogs remaining at large, and partly because this had reportedly cost more than £800 per hedgehog in taxpayers' money.
The biggest barrier to the continuation of the cull however was not financial, but emotional. Many people - both on the islands and elsewhere - were angry that the hedgehog, an otherwise harmless mammal, was being targeted and killed at the same time as it was disappearing from much of mainland Britain.
So in the same year as the cull began, a coalition of animal welfare organisations and charities formed Uist Hedgehog Rescue (UHR).Tender trapping
UHR agreed that hedgehogs were causing problems to wading birds on the islands, but offered an radical alternative solution: instead of killing the animals, why not trap them and relocate them to the mainland, to help boost declining populations there?
During the next three years they relocated more than 700 hedgehogs, and once they had shown that relocation was both feasible and effective - and most importantly did not cause any problems such as the spread of disease back to the mainland population - then in February 2007 the cull was halted.
Instead of killing the animals, Scottish Natural Heritage began to fund the translocation project run by UHR instead. So far about 1600 hedgehogs have been safely removed from the islands and relocated elsewhere.
But what might appear to be a triumph of common sense over a knee-jerk reaction against 'illegal immigrants' may be more complicated than it looks.
In February 2010, hedgehog expert Hugh Warwick, questioned the validity of the original hypothesis. Although no one would deny that hedgehogs do take the eggs of ground-nesting birds, does that necessarily mean that the rapid decline in breeding waders has been caused by the arrival of the hedgehogs?
He suggested that other factors - including changes in farming methods and climate change - might be equally, if not more, to blame than the hedgehogs. Might the hedgehogs even have become convenient scapegoats?
Earlier this year Scottish Natural Heritage announced that it was increasing funding into research on the decline of waders on the Uists.
According to the organisation, this is specifically because there are "still a number of unanswered questions about the full extent of predation on Uist waders, and the degree to which hedgehogs are responsible."
The British Trust for Ornithology in Scotland is also involved in trying to find the root cause of the waders' decline.
With many hedgehogs still at large on the islands, and a fear that the animals are becoming more firmly established on North Uist, this investigation could not be timelier.
Meanwhile trapping of hedgehogs continues, and those captured are still being relocated to the mainland rather than killed.
Whether the hedgehogs are fully, or only partly, to blame for the decrease in the numbers of waders on the Hebrides, one thing is certain: the results of releasing an animal into a new environment can have massive consequences not only for our delicate ecosystems and their wildlife, but also for conservationists, scientists and taxpayers.
Almost forty years on, we still do not know the full implications of that first innocent, but ultimately misguided release.
Hebrides: Islands on the Edge begins on BBC One, Monday 6 May at 2100 BST for viewers in Scotland and is available on iPlayer.