National Mammal Week 2020: Day 10: Islands
Mammal Society Vice Chair and Biosecurity & Invasives Manager of South West Water Kate Hills writes about islands, their endemics and invasive species…
This summer I went to the Isles of Scilly with the family, but also to hunt out a couple of key mammals, the first being the ‘Scilly shrew’. This fascinating little mammal, also known as the Lesser White-Toothed Shrew (Crocidura suaveolens), is the only shrew found in the Isles of Scilly (but is also found on the Channel islands). It was probably introduced by boats, from France or Northern Spain but there are archaeological remains of this shrew from the Bronze Age. This shrew is also distinctive because it does not have red-tipped teeth and is the most grey in colour. They are active day and night and may be heard, even if they are not seen. They are found on the larger islands and I’ve seen them on St Mary’s and Tresco. This shrew can be found in a range of terrestrial habitats where there is suitable cover and can be found on shores. The Scilly shrew is an insectivore and key foods include sand hoppers found along the shore line, and snails and slugs, so may be considered a gardeners friend. Many locals don’t like the shrews in their house and consider them intruding vermin. I was delighted to be given adult and baby Scilly shrew corpses on the last day of my week’s holiday in the Isles of Scilly – which will make guest appearances at Cornwall and Devon Mammal Group events (when we are allowed to meet again).
Invasive Non-Native Species (INNS) are plant or animals (terrestrial, fresh water or marine) that have been moved from their place of origin by humans, accidentally or intentionally, and have a negative impact on the environment, the economy or health. INNS can thrive if they have no natural predators, competitors or diseases to control them and they can have a greater impact on islands as island species can be small, localised or highly specialised and therefore more vulnerable. Invasive mammals can have a disproportionately large impact and there are three INNS mammals in the Isles of Scilly: brown rat, rabbit and hedgehog.
Brown rat (Rattus norvegicus)
The brown rat is one of the most successful mammals world-wide, occupies a range of rural and urban habitats and has a close association with humans. Rats are recognised pests with negative economic impacts on food, crops and property. They also impact on human health and spread disease. They can have a negative impact on the environment and in 2013 the Isles of Scilly Seabird Recovery Project was established to protect shearwaters, petrels and puffins. Rats were successfully eradicated from St Agnes and Gugh and chicks were successfully recorded in 2014. We only saw a live rat once on this trip, on a small island, at high tide, on our nearest beach Porthloo.
Rabbit (Oryctolagus cuniculus)
Rabbits have recently been confirmed as being introduced to GB by the Romans. They have long been associated with islands, where they introduced as a food store; such islands were often called Coney Island – coney is an old name for rabbit. Rabbits are found in a wide vary of habitats, but are most abundant in short grassland and arable fields, especially where there is cover such as hedges or scrub. They can be considered agricultural or garden pests. They are found on a number of the islands, and although not often seen they leave visible droppings. We regularly saw rabbits in a couple of places on St Marys, but only 2 each time; I thought they would be more abundant. Rabbits are widespread in GB, however, they are declining and there are concerns and they are classified as ‘near threatened’ in Scotland and ‘vulnerable’ in England, on the IUCN* red list.
Hedgehog (Erinaceus europaeus)
The hedgehog, probably GB’s most distinctive mammal, is the second mammal we were on the lookout for on our holiday, as my 10 year old daughter had never seen a live one. Hedgehogs can be found in a range of rural and urban habitats. Although native to the mainland, hedgehogs are not native to the Isles of Scilly and are believed to have been introduced to St Mary’s in the 1980s. Many welcome this charismatic species, especially as a gardener’s friend eating slugs and snails. However, hedgehogs can pose a threat to beetles, shrews and ground nesting birds, eating eggs and young chicks. Hedgehogs were also introduced to the Outer Hebrides in the 1970s. A control programme started in 2000 and they hope that North Uist will be confirmed as hedgehog free this year, after two years of monitoring. Hedgehogs are only found on the one island in the Scillies and do not appear to have a negative impact that warrants a control programme. My daughter and I were delighted to have a hedgehog visiting our garden regularly. Although hedgehogs are widespread in Great Britain, they have declined significantly and are considered ‘vulnerable’ on the IUCN red list.
Other islands in the UK have their own specialities and invasive species – such the Orkney vole (Microtus arvalis orcadensis), a subspecies of the common vole (Microtus arvalis) which is found there and the Channel Island of Guernsey. Stoats (Mustela erminea) were first recorded in Orkney in 2010 and have established well, causing significant problems as the only ground predator, to this vole and many birds. Following a review to assess the wildlife risks posed by stoats in 2014, The Orkney Native Wildlife Project was initiated; an ambitious partnership project to eradicate stoats. Scotland has a history of invasive mammal eradication programmes including for the American Mink (Neovison vison) with the Hebridean Mink Project in 2001 and the Shiant Isles Recovery Project from 2014- 2018 to eradicate the black rat (Rattus rattus), both programmes to promote bird conservation.
Wales too has an endemic species, the Skomer vole (Myodes glareolus skomerensis), a sub species of the bank vole (Myodes glareolus), which is larger than the bank vole and, having no ground predators, can be less shy. Finally, there is the greater white-toothed shrew (Crocidura russula), which is found on the Channel Islands of Guernsey, Alderney and Herm as well as Ibiza and Gran Canaria (where it was introduced). These small mammals are found in a range of habitats across Europe and North Africa. In the Channel Islands, they show a preference for being near humans and in farm buildings. I suspect they may be viewed in the same way as the Scilly shrew.
* The International Union for Conservation of Nature (IUCN) is an independent, worldwide organisation that supports the integrity and diversity of nature.
What can you do to help?
Islands and mammals are both magnets for attention. As ever, please help track the status of mammals and send details of sightings (dead or alive) or their signs by using Mammal Mapper our FREE app – find out more about the app/download it here