The flora and fauna of the Outer Hebrides in northwest Scotland comprises a unique and diverse ecosystem. A long archipelago, set on the eastern shores of the Atlantic Ocean, it attracts a wide variety of seabirds, and thanks to the Gulf Stream a climate more mild than might be expected at this latitude. Because it is on the Gulf Stream, it also occasionally gets exotic visitors.

Wildlife

Birds

Three hundred and twenty-seven species of birds have been recorded in the Western Isles and more than 100 breed. The islands provide a natural flyway for migrating landbirds to and from their Arctic breeding grounds and a refuge for windblown vagrants from America and northern Europe. Many species of bird breed in the Western Isles and the surrounding islands, including, most of Britain's corncrakes which breed on the croftlands of all the islands. Local Authority Web Site

Many species of seabirds inhabit the coastal areas of the islands, such as shag, northern gannets, northern fulmars, kittiwakes, guillemots and multiple species of gull.

In the Uig hills in Lewis, it is possible to spot golden eagles; it has also been claimed that white-tailed eagles have been seen in the area. Isle-of-Lewis.com In the Pairc area, it is possible to see feeding Eurasian oystercatchers and Eurasian curlews.

A few pairs of peregrine falcons survive on coastal cliffs and merlin and common buzzard are not uncommon anywhere on hill and moor. Red-throated divers nest on countless small tarns and a few black-throated divers can be found on bigger lochs. Arctic skuas are spreading south from Lewis as far as South Uist but the great skua is still found breeding only in Lewis, St Kilda, North Rona, the Shiant Isles and Barra Head.

An important feature of the winter bird life is the great diversity of wildfowl. A variety of duck, such as common eider and long-tailed duck are found in the shallow water around Lewis.

Great Bernera hosts numerous seabird species, including gulls, waders and ducks such as goldeneye. More unusually, a jack snipe was observed on the island in 2007." Bird Sightings : Hebrides : December 2007" thewesternisles.co.uk. Retrieved 20 June 2008.

The Shiant Isles have a large population of seabirds, including tens of thousands Atlantic puffins breeding in burrows on the slopes of Garbh Eilean, as well as significant numbers of common guillemots, razorbills, northern fulmars, black-legged kittiwakes, common shags, gulls and great skuas. Although St Kilda has more puffins, the sheer density on the Shiants is greater.

Berneray (North Uist) The crofting practises on Berneray encourage a wide array of birdlife. On early summer evenings, you can sometimes hear snipe drumming and even the rasp of a corncrake. Mute swans can be seen on Loch Brusda, and greylag geese are common. In the winter they are joined by barnacle, and a few brent geese. Ravens and buzzards are often to be seen. Golden eagles and hen harriers are rarer sights, usually in the winter. Wading birds on the shore include redshanks, sanderlings, turnstones, oyster catchers, dunlin, curlews, whimbrels, ringed plovers and herons. Further out, around the shores of Berneray, are mallards, eiders, red-breasted mergansers, and, more rarely, black-throated and great northern divers. Shags and cormorants fish in the seas around Berneray throughout the year, and in summer you can see gannets diving.

St Kilda

St Kilda is a breeding ground for many important seabird species. The world's largest colony of gannets, totalling 30,000 pairs, amount to 24 percent of the global population. There are 49,000 breeding pairs of Leach's petrels, up to 90 percent of the European population; 136,000 pairs of Atlantic puffins, about 30 percent of the UK total breeding population, and 67,000 northern fulmar pairs, about 13 percent of the UK total.Benvie, Neil (2000) Scotland's Wildlife. London. Aurum Press. Dùn is home to the largest colony of fulmars in the UK. Prior to 1828, St Kilda was their only UK breeding ground, but they have since spread and established colonies elsewhere, such as Fowlsheugh.Fisher, James & Waterston, George (Nov. 1941) The Breeding Distribution, History and Population of The Fulmar (Fulmarus glacialis) in the British Isles. Edinburgh. The Journal of Animal Ecology, Vol. 10, No. 2 pp. 204–272. Retrieved 24 March 2007. The last great auk (Pinguinus impennis) seen in Britain was killed on Stac an Armin in July 1840. Unusual behaviour by St Kilda's bonxies was recorded in 2007 during research into recent falls in the Leach's petrel population. Using night vision gear, ecologists observed the skuas hunting petrels at night, a remarkable strategy for a seabird.McKenzie, Steven "Bird night attacks may be unique" (5 November 2007) BBC News. Retrieved on 6 November 2007. A subspecies of Eurasian wren, the St Kilda wren Troglodytes troglodytes hirtensis, is unique to St Kilda.

Marine life

Salmon frequent several Lewis rivers after crossing the Atlantic. Many of the fresh-water lochs are home to fish such as trout. Other freshwater fish present include Arctic char, European eel, 3 and 9 spined sticklebacks, thick-lipped mullet and flounder.

Offshore, it is common to see seals, particularly in Stornoway harbour, and with luck, dolphins, porpoises, sharks and even the occasional whale can be encountered.

Occasional turtles, mainly loggerhead and leathery, may be met in coastal waters.

In Great Bernera, sea life is especially rich where there is tidal run between the Caolas Bhalasaigh (English: "Valasay Straits/Kyles") and the inner sea-loch of Tòb Bhalasaigh. There are numerous molluscs, sponges, brittlestars and starfish, the latter growing noticeably larger in size than normal. Cup coral, snakelocks anemone and dead man's fingers coral, may also be found here. Common fish include shanny and butterfish and Atlantic and common seals are regular off-shore visitors.The Outer Hebrides Handbook and Guide (1995) Kittiwake. pp 97–102.

Common seals often congregate at low tide on the rocks in Bays Loch in Berneray (North Uist), grey seals, which are larger and can be distinguished by the long noses, are also to be found there occasionally, but are more common off the West Beach. The grey seal now breeds on Hirta but did not do so before the 1930 evacuation.Fraser Darling, F. and Boyd, J.M. (1969) Natural History in the Highlands and Islands. London. Bloomsbury.

The beach at Village Bay in St Kilda is unusual in that its short stretch of summer sand recedes in winter, exposing the large boulders on which it rests. A survey of the beach in 1953 found only a single resident species, the crustacean isopod Eurydice pulchra.Gauld, R. Bagenal, T.E. and Connell, J.H. (1953) "The marine fauna and flora of St. Kilda, 1952". Scottish Naturalist 65 pages 29–49, quoted in Darling and Boyd (1969) page 184.

Amongst the more exotic species found off the Outer Hebrides, is the giant squid (Architeuthis) – specimens are occasionally washed up on the islands.

Land mammals

Eurasian otters and red deer are the Western Isles' native land mammals. Humans introduced species such as European rabbits, blue hares, hedgehogs, brown and black rats, feral cats, minks and polecats. Other species such as mice and voles are of unclear origin.

There has been considerable controversy over hedgehogs on South Uist. The animals are not native to the islands, having been introduced in the 1970s to reduce garden pests. They now pose a threat to the eggs of ground nesting wading birds on the reserve. In 2003 Scottish Natural Heritage undertook a cull of hedgehogs in the area.Epping Forest Hedgehog Rescue Retrieved 1 January 2007.Ross, John (21 February 2007) Hedgehogs saved from the syringe as controversial Uist cull called off. Edinburgh. The Scotsman newspaper.

American mink are another introduced species (escapees from fur farms) and cause problems for native ground-nesting birds, the local fishing industry and poultry farmers. Due to this impact and following a successful eradicationBBC News of the species from the Uists and Barra, the second and ongoing phase of the Hebridean Mink Project aims to rid mink from Lewis and Harris in similar fashion.

The Shiant Isles were home to a colony of black rats, which may originally have come ashore from a shipwreck.Haswell-Smith, Hamish (2004) The Scottish Islands. Edinburgh. Canongate. Apart from one or two small islands in the Firth of Forth, the Shiants were the only place in the UK where the black rat or ship's rat (Rattus rattus) could be found. There were thought to have been about 3,000 rats on the islands. Analysis of their stomach contents demonstrated that the Shiant rats did eat seabirds, but it is impossible to tell if they preyed on live birds or simply scavenged dead remains.Stapp, Paul (2002) "Stable isotopes reveal evidence of predation by ship rats on seabirds on the Shiant Islands". Scotland Journal of Applied Ecology 39 (5), 831–840. Following a program between 2014 and 2018 run by the RSPB, Scottish Natural Heritage and the custodians of the Shiants, the Nicolson Family the Shiants were officially declared free of the black rat."Shiant Isles Recovery Project" RSPB Retrieved 09 June 2021.

A subspecies of wood mouse known as the St Kilda field mouse (Apodemus sylvaticus hirtensis) is unique to St Kilda. A subspecies of house mouse known as the St Kilda house mouse (Mus musculus muralis), vanished completely after the evacuation of human inhabitants, as it was strictly associated with settlements and buildings. It had a number of traits in common with a sub-species (Mus musculus mykinessiensis)"The mammals on Mykines" Heima.olivant.fo. Retrieved 22 May 2007. found on Mykines island in the Faroe Islands.

The St Kildans kept up to 2,000 sheep, which were removed at the time of the evacuation, but a herd of 107 indigenous Soay sheep were transferred onto Hirta from Soay and now live in a feral state. Soay sheep are a very primitive breed that do not require shearing. Numbers vary from 600 to 1,700 on Hirta, and 200 remain on Soay. A few have been exported to form breeding populations in other nations, where they are valued for their hardiness and small size."Soays of America" soaysofamerica.org Retrieved 24 December 2007. On Hirta and Soay, they prefer the plantago pastures, which grow well in locations exposed to sea spray and include red fescue, sea plantain and sea pink. There is also a breed of feral sheep residing on Boreray, which is one of the most endangered British sheep in existence."Livestock breeds" Oklahoma State University Department of Animal Science. Retrieved 15 March 2007.Quine (2000) page 30.

There are claims that the Stornoway castle grounds are home to bats. In addition, there are farmed animals such as sheep, cattle and a few pigs.

Reptiles and amphibians In common with Ireland, no snakes inhabit Lewis,Morris, Dr P. (1984). Animals of Britain, Field Guide to the. London: Reader's Digest Association only the slowworm which is merely mistaken for a snake. Actually a legless lizard, it is the sole member of its order present. The common frog may be found in the centre of the island though it, along with any newts or toads present are introduced species.

Insects

The island's most famous insect resident is the Highland midge which is ever-present near water at certain times of the year.

During the summer months, several species of butterflies and dragonflies can be found, especially outside Stornoway.

The richness of insect life in Lewis is evident from the fact that carnivorous plants, such as the sundew, thrive in parts of the island.

Plant life