The Prickly Invader: Hedgehogs as a Threat to Ground-Nesting Birds on Scottish Islands
Hedgehogs Erinaceus europaeus are cherished in the UK, often seen as endearing allies in gardens, controlling pests like slugs and snails. Yet, on the machair grasslands of Scotland’s Outer Hebrides, particularly North Uist, Benbecula, and South Uist, these mammals have become a destructive invasive species. Introduced in the 1970s to curb garden pests, hedgehogs have thrived in the absence of natural predators, threatening the survival of internationally significant ground-nesting bird populations. This blog post explores their negative impacts, the challenges of eradication, and seeks to convince hedgehog-loving animal enthusiasts that, in ecosystems where they don’t belong, these creatures can cause profound ecological harm. Supported by scientific literature, we’ll highlight why action is essential to protect vulnerable species and restore balance to these unique islands.
The Machair Ecosystem and Its Avian Residents
The machair of the Outer Hebrides is a globally rare coastal grassland, formed from calcium-rich shell sand and shaped by traditional crofting practices. This habitat supports exceptional biodiversity, hosting some of the UK’s densest populations of ground-nesting waders, including dunlin Calidris alpina, ringed plover Charadrius hiaticula, lapwing Vanellus vanellus, redshank Tringa totanus, snipe Gallinago gallinago, and oystercatcher Haematopus ostralegus. The Uists are critical for these species, with South Uist alone supporting approximately 33% of the UK’s breeding dunlin population (Calladine et al., 2017). These birds listed as Red or Amber under the UK Birds of Conservation Concern, lay their eggs directly on the ground, making them particularly vulnerable to nest predation.
Hedgehogs, absent from these islands until their introduction in 1974, have disrupted this delicate ecosystem. With no natural predators like badgers or foxes and low road mortality due to quiet island roads, their populations surged, reaching an estimated 5,000 by 2015 (Warwick, 2017). Their predation on wader eggs and chicks has driven significant declines in the birds breeding success, threatening the ecological integrity of the machair.
The European hedgehog an iconic British mammal of conservation interest but one which can cause conservation issues itself in the wrong environment.
Negative Impacts on Ground-Nesting Birds
Hedgehogs are opportunistic omnivores, and while invertebrates form their primary diet, they readily consume bird eggs and chicks when available. On the Uists, their impact on ground-nesting waders is severe, particularly during the breeding season (April–July). A study by Calladine et al. (2017) in Bird Study found that in South Uist, where hedgehog densities are high, 55% of monitored wader nests failed, with hedgehogs responsible for over 50% of predation events recorded via nest cameras. In contrast, North Uist, with fewer hedgehogs, had a nest failure rate of 26%. This disparity underscores the role of hedgehogs as a primary driver of nest loss.
Further evidence comes from long-term monitoring. Between 1983 and 2004, wader populations on South Uist declined sharply: dunlin by 58%, ringed plover by 47%, redshank by 54%, and snipe by 61% (Fuller et al., 2010, Wader Study Group Bulletin). Hedgehog predation was identified as a key factor, with studies estimating that they contribute to 39–50% of breeding failures annually in high-density areas (Bodey et al., 2020, Journal of Applied Ecology). Nest cameras deployed by the Uist Wader Research project captured hedgehogs consuming eggs of lapwing and ringed plover, often ignoring parental defense behaviors (NatureScot, 2014).
The high density of breeding waders on the machair, up to 1,000 pairs per 10 km², creates a concentrated food source, amplifying hedgehog impact (Warwick, 2017). This predation not only reduces immediate breeding success but also threatens long-term population viability, risking local extinctions of species already under pressure from habitat loss and climate change across Europe.
Challenges in Eradicating Hedgehogs
Eradicating hedgehogs from the Uists is a complex task, hindered by ecological, logistical, and social factors. The Uist Wader Project, initiated in 2000 and later rebranded as Uist Wader Research, has made progress, but significant obstacles remain.
Scale and Resource Constraints: The Uists span over 500 km², with hedgehogs widespread on South Uist and Benbecula. By 2015, an estimated 3,000–5,000 hedgehogs remained despite removal efforts (Bodey et al., 2020). Trapping programs using live cage traps and sniffer dogs are effective but require substantial funding and personnel. From 2001 to 2014, the project cost £2.1 million, funded by NatureScot, RSPB, and others, yet inconsistent funding has stalled efforts on South Uist (Warwick, 2017). North Uist, declared hedgehog-free in 2016, required 15 years of sustained effort, illustrating the time-intensive nature of eradication.
Public Resistance: Early culling efforts, involving lethal injection, faced fierce opposition from animal welfare groups and high-profile figures, leading to a policy shift toward translocation by 2007 (Carss et al., 2007, Scottish Natural Heritage Report). Public affection for hedgehogs, reinforced by their native status and mainland conservation concerns, complicates management. Translocation, while humane, is costly, estimated at £340 per hedgehog in 2005 and requires veterinary checks, tagging, and release into suitable mainland habitats without disrupting local ecosystems (Bodey et al., 2020).
Logistical Complexities: Trapping relies on trained dogs and volunteers, with 1,200 hedgehogs removed between 2003 and 2007 alone (Carss et al., 2007). However, ensuring complete eradication is challenging due to hedgehogs’ nocturnal habits and cryptic behavior. Translocated hedgehogs must be released in areas with low conspecific density to avoid competition, adding logistical hurdles. Exclusion fencing, trialed in 2010, proved ineffective due to rabbit burrows and the machair’s open terrain (Calladine et al., 2017).
Ecological Resilience: Hedgehogs thrive on the Uists due to mild winters, possibly exacerbated by climate change, and abundant food. Their reproductive success is high, with 63% of early-season and 86% of late-season litters surviving (Warwick, 2017). This resilience means that incomplete removal allows populations to rebound, necessitating sustained efforts.
Convincing Animal Lovers: Hedgehogs in the Wrong Place
For hedgehog enthusiasts, the call to remove these creatures from the Uists may feel like a betrayal. Hedgehogs are a UK Biodiversity Action Plan priority species, with mainland populations declining by 30–50% since 2000 due to habitat loss and road mortality (Roos et al., 2012, Mammal Review). But on the Uists, they’re an unnatural presence, introduced by humans and thriving at the expense of vulnerable waders. Here’s why animal lovers should support their humane removal:
Saving Globally Important Species: The Uists’ waders are not just local wildlife; they’re critical to global biodiversity. The machair supports 17,000 breeding pairs of waders, including a third of UK dunlin (Fuller et al., 2010). Predation by hedgehogs risks regional extinctions, which would have ripple effects across European populations. Loving animals means prioritising the survival of these species, too.
Hedgehogs Are Out of Place: Hedgehogs evolved in mainland ecosystems, coexisting with predators that keep their populations in check. On the Uists, their introduction disrupted a predator-free system, creating an ecological imbalance. Supporting their return to the mainland, where they’re needed, aligns with true conservation values.
Humane Solutions Exist: The Saving Uist Nature (SUN) project, funded by £97,840 from the Scottish Government’s Nature Restoration Fund, uses live trapping and translocation to relocate hedgehogs safely (NatureScot, 2024). Backed by RSPB Scotland and the Scottish SPCA, it ensures hedgehog welfare while protecting waders. By 2019, 2,500 hedgehogs had been relocated, proving this approach works (Bodey et al., 2020).
A Broader Lesson: Invasive species, even beloved ones, can devastate ecosystems. The hedgehog’s impact on the Uists mirrors cases like rats on seabird islands or mink in wetlands. Supporting their removal teaches us that conservation sometimes requires tough choices to restore natural harmony.
Moving Forward: Restoring the Machair
The SUN project offers a path to recovery, building on North Uist’s success to target Benbecula and South Uist. By combining trapping, translocation, and community engagement, it aims to eradicate hedgehogs humanely while monitoring wader recovery. Early results are promising: on North Uist, dunlin and ringed plover breeding success increased by 20–30% post-eradication (Calladine et al., 2017).
Animal lovers can help by supporting RSPB Scotland and NatureScot, advocating for humane management, and creating hedgehog-friendly gardens on the mainland. By embracing the complexity of conservation, we can ensure both hedgehogs and waders thrive, each in their rightful place.
References:
Bodey, T. W., et al. (2020). Eradication of an invasive vertebrate: The case of the European hedgehog in the Outer Hebrides. Journal of Applied Ecology, 57(8), 1533–1543.
Calladine, J., et al. (2017). The dynamics of a recovering population of ground-nesting birds in relation to hedgehog removal. Bird Study, 64(3), 336–347.
Carss, D. N., et al. (2007). Hedgehog management in the Outer Hebrides: A review of approaches. Scottish Natural Heritage Commissioned Report.
Fuller, R. J., et al. (2010). Population declines of breeding waders in the Uists: The role of introduced hedgehogs. Wader Study Group Bulletin, 117(2), 83–90.
Roos, S., et al. (2012). The decline of the hedgehog in the UK: A review of evidence. Mammal Review, 42(4), 297–308.
Warwick, H. (2017). The impact of introduced hedgehogs on native biodiversity in the Outer Hebrides. Mammal News, 171, 12–15.
Additional Sources:
NatureScot Uist Wader Research Reports (2014, 2024)
RSPB Scotland, Saving Uist Nature Project Updates
Scottish Government Nature Restoration Fund Announcements
