Rhoda Meek: There are no rabbits in Tiree

Here, on the other side of the Gunna Sound, even pet rabbits are viewed with suspicion. We don’t want rabbits, nor do we want their holes. Instead, we have hares, and we have no truck with them.

They cause very little damage unless you have an unprotected veg patch – and even then they are almost mannerly when compared to your average voracious rabbit. Critically, they don’t dig.

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Rabbits might be off-limits, but other species have invaded. Once upon a time, Tiree had no frogs, no toads and no hedgehogs. Thanks to the questionable genius of human beings, all three species are now firmly resident.

My dad tells the story of the first time he came face to face with a toad in one of our damp outbuildings. He thought he was losing the plot, and had to call the “bird man” (RSPB officer) to satisfy himself that he wasn’t seeing things.

Toads at our end of the island remain fairly rare, but the frogs have expanded their territory everywhere – as have the hedgehogs. Tales about how these creatures arrived vary. The amphibians tend to be blamed on science projects at the school, and a former vet has been credited with the hedgehog release.

Regardless of blame, too much time has passed for their origins to make any substantive difference. They are here, and unlikely to go anywhere.

In a number of islands, hedgehogs are an absolute menace to nesting birds because – as my hen house discovery one morning will attest – they are awfully fond of eggs. My invader was enormous. I suspect he had been dining there quite regularly. He was gently relocated.

We don’t have the same level of risk to our ground-nesting birds precisely because we don’t have rabbits. It’s thought that a lack of burrows means that hedgehogs are more exposed to the elements and as a result raise fewer young. It means that they are here, but that we are not overrun.

The same can’t be said for Uist, blessed as they are with both rabbits and hedgehogs.

Last week came the news that hedgehogs in Uist are to be fitted with GPS trackers so that scientists can better understand their movements. The goal is to be able to capture them more easily, and relocate them.

This is not Uist’s first rodeo with the prickly pests. They have been waging a war against hedgehogs for more than two decades. Reportedly introduced to the islands in the 1970s by a well-meaning gardener hoping to control slugs (a similar story unfolded in North Ronaldsay), the small population exploded in the absence of natural predators. By the late 1990s, an estimated 10,000 hedgehogs were roaming the islands, feasting on the eggs of birds such as lapwings, redshanks and dunlins.

Various eradication attempts followed – electric fences, sniffer dogs, even a controversial bounty scheme which offered a fiver for a dead hedgehog – but the spiky invaders proved tenacious. Lethal control was eventually abandoned after a backlash, and efforts shifted towards trapping and relocation. North Uist is now thought to be hedgehog-free, but an estimated 4000 remain in Benbecula and South Uist – hence the latest high-tech exercise.

In 2015, a NatureScot (formerly Scottish Natural Heritage) report found that wader clutch survival rates were higher in North Uist (low hedgehog density) compared to South Uist (high hedgehog density), suggesting a positive impact of hedgehog removal on wading birds, however, caveats around gull predation and other factors remained.

Hedgehogs are far from the only species to have thrown island ecosystems into chaos. Where hedgehogs sneak into nests for eggs, American mink brought full-scale destruction. First introduced to Scotland for fur farming in the mid-20th century, they escaped into the wild. With no natural predators, they spread across Lewis, Harris, and North Uist, decimating populations of ground-nesting birds such as terns, lapwings and corncrakes.

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Realising that something had to be done, conservationists launched the Hebridean Mink Project in 2001, a large-scale exercise to trap and remove mink from the islands. Twenty-four years later, they have been successfully eradicated from Uist and Barra, and numbers in Lewis and Harris are now dramatically reduced – although they remain closely monitored.

This isn’t the only success story in the fight against invasive predators. The Isle of Canna, home to important seabird colonies, suffered for decades from a rat infestation that wiped out entire populations of birds like storm petrels and Manx shearwaters. In 2005, a bold eradication programme was launched, using carefully controlled baiting to remove every last rat from the island. The project no doubt benefited from the island being smaller than most, and by 2008, Canna was declared rat-free. The seabirds have been making a steady comeback ever since.

The Canna rats most likely arrived unknown on a boat and this is just one example of how small human actions – deliberate or accidental – can have huge consequences. It could be argued that the same applies to species reintroduction. Where a species has been absent for a long time, its reintroduction can have a dramatic, and not always positive, effect on the ecosystem where it once fitted.

The reintroduction of wolves to Yellowstone National Park in the 1990s is one of the most well-documented examples of how returning a lost species can restore balance to an ecosystem. After being hunted to extinction in the early 20th century, wolves were brought back to the park. Controversial at the time, their presence resulted in positive changes. Elk populations, which had grown unchecked, were kept in balance, allowing vegetation to recover and creating better conditions for beavers, birds and other species. Even coyotes, which had flourished in the absence of wolves, saw their numbers controlled.

It’s a striking success story but crucially, it was a carefully managed, science-led process with long-term monitoring. That reintroduction is in stark contrast to the ongoing debates over sea eagle reintroduction here in Scotland, where some farmers and crofters report devastating losses of lambs.

That lesson seems particularly relevant now, as the release of feral pigs near Kingussie also made headlines last week. They were found in the same vicinity as the four lynx illegally released last month. The lynx were captured and rehomed (one died). The pigs were less fortunate. They were caught and culled.

However, other boars are out there. NatureScot says that there are at least four separate breeding populations, located in Lochaber, Dumfries and Galloway, and Ross-shire, where they have either been released illegally or escaped from farms. A story broke in December of ones weighing up to 32 stone digging up gardens and terrorising dog walkers in the Great Glen. Apparently, they can reach a top speed of 20mph. It makes the toad which caused my dad to jump pale into insignificance, and had me checking the date in case it was the first of April.

We can only hope that whoever is behind these most recent reckless releases is found before they do any more damage. Because when it comes to species introductions of any sort – however well-intentioned – history shows that once the frog is out of the bucket, you’ll never get it back in.