Wildlife

Wildlife overview

What makes Scilly special for wildlife?

Scilly has a unique assembly of native, migrant and introduced species. The sea surrounding Scilly isolates it from mainland Britain and the warm North Atlantic Drift current keeps the islands frost-free. In three areas around Scilly - the Irish Sea Front, the Ushant Front and the Continental Shelf - cold nutrient-rich waters mix with the warmer water of the North Atlantic Drift current. The combination of warmth and nutrients encourages the growth of phytoplankton (microscopic plants) which are a rich food source for planktonic animals and turns these three areas into feeding grounds for fish, sea birds and sea mammals living in and around Scilly. However, the tidal currents that circle round Scilly isolate it from these feeding grounds and Scilly lacks any rivers or estuaries to fertilize the coastal water. These geographical features account for the clear blue of the sea and limit the numbers of seashore species; they also hamper attempts to farm mussels and oysters here.

The history behind Scilly’s wildlife

In the last Ice Age, 20,000 years ago, the Atlantic coast was 100 km west of Scilly. At that time, Scilly, Ireland, Britain, mainland Europe and Scandanavia were all joined. An ice sheet covered most of Britain, just reaching the north ends of Tresco and St Martins. The plants and animals that lived where the Scillies are now were characteristic tundra wildlife (BBC Pleistocene wildlife video) and some of these, lichens, Dwarf Pansy, Greater Tussock Sedge and Red barbed ant remain in the islands.

After the last Ice Age, changes in climate and sea level isolated Scilly, first from continental Europe and then from mainland Britain, restricting the numbers of land animals and allowing some species to evolve separately and differently, giving rise to unique species special to Scilly (endemic species).

Since Neolithic times, human activity has linked Scilly with the rest of the world, importing alien species, both accidentally and intentionally, creating the extraordinary array of plants and animals that thrive in the comparative warmth offered by the North Atlantic Drift current.

These features of Scilly’s geography and history have shaped Scilly’s flora and fauna so that the wildlife we see here today covers a complete range from the exclusive, ‘endemic’ species, like the Scilly shrew, through nationally rare species such as the giant gobi, Lesne’s earwig, many lichens, red seaweeds and mosses, to common species such as shore crab and bracken. Scilly also houses what are arguably out-of-place alien imports such as stick insects and the pittosporum trees that are used as windbreaks.

Read more about unsual species >>

Explorers and colonizers

The seashore presents many challenges to its wildlife. How do the seashore animals arrive and stay on the part of Scilly’s rocky and sandy coastline that suits them best?

Seashore animals use a variety of breeding strategies to ensure the young remain in the preferred habitat and colonise new habitats as they become available: seahorses, rock periwinkles, and sandhoppers hold their eggs in brood pouches until they hatch; lugworm females lay their eggs in their burrows, where they hatch and develop a little before being washed to nearby sites; plaice, limpets and sea urchins broadcast eggs and sperm and their fertilized eggs are the start of a planktonic phase of their life cycle. Most marine invertebrates have planktonic larvae which are microscopic and are poor swimmers but hitch rides on different currents by moving up or down, arriving back in Scilly when they are ready to settle in their new habitat on the shore.

Seashore breeding strategies

Planktonic larvae

Endemic Scillonian wildlife

Scilly has been isolated from mainland Europe for 17,000 years and from mainland Britain for about 7,000 years. In this time some species have changed genetically making them ‘endemic’ (unique) to the islands. Some changes visibly alter their shape, colour or behaviour, others are only detectable biochemically as changes in DNA and proteins. The Scilly Shrew, St Martins Ant, Scillonian Specked Wood Butterfly, Scilly Bee, Shore Dock, Sea Rush and St Martins Buttercup are all different to varying extents from their mainland or European counterparts and are unique to Scilly. Studying these differences in local populations can help guide conservation strategies.

Alien invaders?

Many plants you may associate with Scilly are not native to the islands but were brought here from South Africa (hottentot fig), from New Zealand (pittosporum), or from California (Monterey pine). These plants have naturalized in Scilly and provide food and shelter for native wildlife. However, alien species can be a threat, by competing with native species or by interbreeding with species that are unique to Scilly. As well as resident and migrant wildlife, many vagrant species of birds, turtles and some insects pass through Scilly, finding food and shelter here. Occasionally, such vagrancy leads to colonisation, as has happened in the past, for example with the Eastern Collared Dove in the 1960s, and may be happening now with the Little Egret.

Timeline of arrivals and introductions >>