The bats of Sherkin Island
Due to the presence of the sea, islands are extremely difficult places for terrestrial mammals to colonize. If the island is close enough to the mainland then some can swim across, such as the case of foxes on Sherkin and badgers on Coney Island. Of course semi aquatic mammals such as the otter can colonize islands much farther out and because of this were probably one of the earliest mammalian colonists to reach Ireland at the end of the last ice age.
Most mammals rely on human aided transportation to get there, either intentionally in the case of rabbits or accidentally in the case of the wood mouse. But due to their ability to fly, bats are one mammal group for which colonization of islands shouldn’t be a problem. Bats are the only mammals that can truly fly. Their wings are actually modified arms with elongated finger and wrist bones making up the basic structure and support for a double membrane of skin which envelopes them. Aerodynamically, bat wings act like sails on a boat, catching the wind and, because of the presence of fingers, are much more maneuverable in flight than bird wings. This ability to fly has allowed bats to colonize every continent in the world except the Antarctic.
Bats belong to the order Chiroptera, which means hand wing. This order is extremely rich and diverse, containing approximately 1,100 species. There are 47 known bat species in Europe, 17 in Britain and 10 in Ireland, making up a third of Ireland’s mammal fauna. Worldwide, these animals can be divided into three groups based on what they eat; fruit eaters, insectivores and carnivores. All bat species in Ireland and Europe eat insects and spiders. In temperate regions of the world where there is a winter and insects are unavailable, bats can go into hibernation during cold periods to avoid starvation and the harsh weather.
Irish islands can be very difficult for bats to live on because they are generally small in size with a limited number of habitats. One of the most important habitats for most bats in Ireland is deciduous woodland. This habitat provides foraging habitat for woodland edge and woodland interior species and roosting sites for both woodland bats and bats that forage in other habitats. Very few of our islands have any substantial tree cover, either due to the harsh winds coming off the Atlantic Ocean that burns the leaves of trees or because of human clearance of the original native woodlands there for the creation of agricultural land or building material and fuel. The pollen records from Lough Ordree tell us that Sherkin was once covered in mixed woodland of oak, pine and hazel and it is likely that the island would have provided suitable habitat for a number of species.
All Irish bat species have adapted to roosting in human dwellings and this may allow some species to live on islands where woodland cover is scarce or absent. The bat fauna of Irish offshore islands is not very well known. Bats are known to occur on Cape Clear (1 resident species and 2 vagrants), Clare Island (3 species) and Rathlin Island (1 species). Sherkin Island’s bat fauna was unknown until quite recently when a survey was conducted in August 2006 by the Cork County Bat Group when four species were found to occur on the island; the common pipistrelle, soprano pipistrelle, brown long-eared and Leisler’s bats. Given the size of the island, this is quite a diverse number of species.
So what is so great about Sherkin Island for bats compared to other offshore islands? Firstly, Sherkin is quite close to the mainland and so is much easier to colonize than say Cape Clear. Secondly, because it lies in the shelter of Roaring Water Bay, trees find it much easier to grow here than Cape Clear, which is much more exposed. Sherkin Island also has some good pockets of elm woodland that provide excellent foraging habitat for the brown long-eared bats that are a woodland interior species that feeds mainly on moths, catching them in flight or by gleaning them off foliage. Sherkin also possesses some freshwater bodies that provide foraging habitat for the pipistrelle species and Leisler’s bat. Leisler’s are likely to be non-resident visitors here due to the small size of the Island, which would probably not be big enough to maintain a resident population.
Bats are threatened both globally and locally from habitat destruction, roost destruction, pollution and human persecution. So what can be done to protect the bat populations on Sherkin? Currently, roosts are at risk due to the renovation of houses, whereby access is prevented due to filling in of entry points during building work. Bat roosts need to be identified and the house owners educated about the beneficial nature of bats so roosts are tolerated and retained during repairs. It should be pointed out that bats are protected under the Wildlife Act 1976 (amended 2000) and it is illegal to disturb bats in their roosts.
Landowners on the island in the Rural Environmental Protection Scheme could plant trees around their farm buildings and hedgerows and treelines along their field boundaries to link up important foraging sites. The creation and expansion of broadleaf woodland would also increase the amount of foraging habitat for bats especially the brown long-eared and potentially provide suitable roosting sites in the future. The protection of existing freshwater bodies from pollution would ensure that their value as bat foraging habitat would be ensured. Again, farmers in REPs could dig new waterbodies which would increase this habitat for bats and other aquatic life such as dragonflies and frogs. The small amount of elm woodland on the island needs to be protected and expanded if possible.
The bats of Sherkin are part of the island’s heritage, just as much as the abbey and other archeological sites. They need to be protected and appreciated. So the next time you are wandering through the elm tree lined road on the way to the Jolly Roger pub keep an eye out for those 'flying goblins of the night' and take some time to observe their skillful flight and precarious existence on a small but diverse island on the edge of the Atlantic.