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Wildlife of Hilbre

1. Birds of Hilbre Island.
2. Wildlife on and around Hilbre Island.
3. Hilbre Islands' Status as a Nature Reserve.

Wildlife on and around Hilbre Island

Thrift and Bird's-foot Trefoil on Hilbre Island © Colin Jones

Introduction
Hilbre has two sorts of wildlife communities: the estuary shores, and maritime heath with grassland. Rocky shores are usually rich in species, but here, the sandstone is crumbly, and so many shellfish (molluscs) cannot attach themselves. Estuarine sea water varies in its salt content at different times of tide, and after heavy rain water run-off from the land. Silt and sand are carried in the water, and moved around from the River Dee and Liverpool Bay. No living species is isolated; there is a complex inter-connection of animals and plants through their food, predation, ideal situation on the shore, etc. Disturbing the balance of one species can upset the whole pattern.

Effects of salinity and salt winds
Some animals are damaged by alterations in salt concentrations in sea water, but shore crabs can stand a range of salinity. Hilbre’s prevailing winds come from the north west, their drying effect damaging to land plants and to shore animals when exposed between tides. The danger comes from winds drying out delicate living organisms as a windy day dries washing. Seaweeds and animals on the shore must shelter or have some protection when exposed by the falling tide. Mechanical wind damage wears away cliffs, its blown sand acting like blast-cleaning a building. This is evident where sandstone walls have worn away in the pattern of the masons’ chisel marks. Salt chemically destroys land plants, and some are adapted to the drying effects by storing water in their leaves, such as purslane and scurvy grass. Sea thrift has the same internal protection against salty soil as other plants have to avoid frost damage. Air temperatures in winter are generally mild because of the effect of a large body of sea water which cools slowly. Snow is rare on Hilbre.

Red beadlet anemone © Val Burnett

Shore invertebrate animals include red beadlet anemones, and worms in sand or stuck to the rocks. These have population cycles, peaking roughly every 20 years. Some shellfish (molluscs) live below the lowest tide levels in the sand and mud. Their shells and egg cases are often washed up, such as whelks and necklace shells. Dog whelks and winkles move over the rocks, feeding on algae, or each other! Mussels and barnacles sieve food from the sea water when covered by the tide. Sabellaria reef worms also filter sea water and build grey crusts on the western shores. Hermit crabs take over empty shells of dog whelks and common winkles. Edible crabs, once common, have almost died out. Shrimps and prawns inhabit pools in the sand.

Seaweeds show their usual shore zonation on Hilbre, with the exception of channelled wrack. On Hilbre, there is only one place where it is locally common, where the soft sandstone rock has a harder seam through it. Bladder wrack and serrated wrack are the least resistant to drying, and so found on the lower shore. Because there are no sub tidal rocks to anchor the plants, Hilbre has no Laminaria (oar weeds or kelps)

Sea vertebrate animals include Atlantic grey seals, occasional dolphins and porpoises, and whales. The Dee supports one of the few British non-breeding colonies of grey seals. Numbers have grown from a few animals in the 1930s to several hundred.

Birds visiting Hilbre in winter include waders, with some species of geese and ducks. Many land and shore birds pass through on their way to warmer winter quarters, and move north again in spring to breed in the long summer days of the Arctic. The land birds include resident breeding species, such as meadow pipit and (sometimes) skylark on the ground, linnets and wrens in the bushes, along with migrants on passage to warmer countries in autumn. Swallows sometimes nest in the buildings. If migrating birds are deprived of food, they quickly starve to death, as their energy needs are so high that they live on the margin of survival. There is often a kestrel hovering while it looks for small rodents such as mice and field voles, or even beetles.

Greenland Wheatear © Colin Jones

Fish species include gobies in the pools, flat fish (plaice, dab and flounder), in the gutters. Hilbre’s only poisonous fish are weevers, which hide under the sand with their stinging spines exposed. Sea fish numbers have fallen in the last 100 years. It is difficult to know whether over-fishing has contributed.

Land mammals seem to be casual visitors to the islands. Foxes and hedgehogs have been seen walking over the shore, and weasel was recorded in the 1960s. Rabbits were introduced in the Middle Ages as food for the monks, but died out in the 19th century. Field voles live in the grassland.

Land plants include sea thrift, yellow birdsfoot trefoil, sea spurrey, buckshorn plantain, white sea campion, and centaury. Ragwort, poisonous to cattle, provides food for the striped caterpillars of cinnabar moth. These support many other butterflies, such as migrating painted ladies. Hilbre’s specialities are the sea spleenwort, growing on sheltered cliff faces, and a sub species of rock sea lavender found in only a few other places in Europe. Small stone walls protect the plants from destruction by waves breaking over the island during storms. Bluebells are hybrids between the native and Spanish types.

Conservation
Please do not pick or collect samples, or light fires. Please walk with care, with dogs always on a lead, take litter home, and avoid disturbing breeding birds and animals by keeping to the path. Your reward will be the enjoyment of watching wild creatures in this unusual island setting. Hilbre is a Local Nature Reserve, and as part of the Dee Estuary is included in a Site of Special Scientific Interest, Special Protection Area, a Ramsar site of world importance for wetland birds and a candidate EU Special Area of Conservation.

© Susan Craggs, 2005

For further information on the biodiversity of Wirral with links to the Hilbre Islands please visit:
www.wirral.gov.uk/ed/biodiversity/home.htm