Mammals Stamp Issue 13th April 2010.

As Royal Mail’s contribution to the International Year of Biodiversity in 2010, our Action for Species series continues with Mammals, which features ten of our most engaging yet endangered indigenous mammals. From the giant Sperm Whale to the tiny Dormouse, each of these species has to contend with dangers caused by man’s continuing incursions into their natural habitats, as well as from predation by non-native species. Conservation efforts have been enormous however, and the stories of their success make this delightful Special issue particularly heartwarming.

First Class - Humpback Whale:- Megaptera novaeangliae

Average weight: 45 tonnes Total length: 13–15m

This big, black whale with white under its tail has knobbly flippers that are longer than those of any other whale. Seen mainly in summer to the west of Britain, it arches its back to dive and feeds by sieving small fish from the water using a complex array of frilly plates found in its upper jaw instead of teeth.

First Class – Wildcat Felis silvestris
Average weight: 5.5–6.5kg Total length: 75–110cm

Shy and nocturnal, and now confined to the wilder parts of Scotland, the wildcat resembles a tabby cat with prominent black stripes on the body and legs. Its tail is thick and round-ended compared to the domestic cat’s thin, pointed tail, but there are many hybrids. Female wildcats can produce one family a year, in spring.

First Class - Brown Long-eared Bat Plecotus auritus
Average weight: 6–10g Total wingspan: 26–29cm

A small fluttery bat with enormous ears, this mammal is found throughout mainland Britain, except for the extreme north of Scotland. It commonly occurs in attics, as well as hollow trees and bird boxes, and often hovers to pick insects and spiders off trees. Completely harmless and a gentle creature, this is the bat most often found flying inside houses.

First Class – Polecat Mustela putorius
Average weight: 700–1700g Total length: 50–60Cm

The polecat has a long, thin body with short legs and a distinctive face pattern. In the summer its overall colour is blackish and cream, becoming paler in winter. Interbreeding with escaped ferrets has produced lighter-coloured varieties. An inhabitant of farmland and hedgerows, mainly in Wales and the West Midlands, it feeds on mice, voles, frogs and small birds.

First Class - Sperm Whale Physeter macrocephalus
Average weight: 15–40 tonnes Total length: 10–15m

The sperm whale, with its huge, blunt-ended head, is normally found in deep waters to the west of Britain, but occasionally strays into estuaries and gets stranded when the tide goes out. Usually solitary, the sperm whale sometimes lives in small groups. After swimming at the surface for about 10 minutes, it then dives deep for half an hour to feed, mainly on squid.

First Class - Water Vole Arvicola terrestris
Average weight: 180–230g Total length: 29–31cm

A rat-sized animal with a chubby face and dark chocolate-brown fur, the water vole is a good swimmer and lives beside ponds, rivers and ditches, where it digs burrows in the banks and feeds on juicy vegetation, roots and bark. It is found mainly in the lowlands, throughout mainland Britain, usually in small colonies.

First Class - Greater Horseshoe Bat Rhinolophus ferrumequinum
Average weight: 15–30g Total wingspan: 33–39cm

Large and broad-winged, this species of bat has a distinctive cone-shaped nose-leaf through which its echolocation sounds are focused. Its wings and ears are pale brown, and the fur is grey or buff, with a reddish tinge in older animals. Found mainly in south-west England and south Wales, it hibernates in caves, cellars and mines from October to May, wrapping its wings around its body while roosting. Its food consists of beetles and other large-bodied insects, caught in flight or snatched from the ground. In summer, females seek out warm places such as barn roofs, where, after a 75-day gestation period, they give birth to a single baby each year, nearly a third of its mother’s weight.

First Class – Otter Lutra lutra
Average weight: 6–8kg Total length: 100–110cm

Large, long and sleek with short legs and webbed feet, the otter is normally seen only in or beside water, where it swims and dives frequently in pursuit of fish, crabs and other aquatic food. More widespread and numerous in western counties, many live along the shores of Scotland’s sea lochs. Otters will usually live alone or in a family group of a female and one to three young.

First Class – Dormouse Muscardinus avellanarius
Average weight: 10–30g Average body length: 12–15cm

This golden-yellow mammal is the only British mouse with a thick fluffy tail. Found mostly in southern England, it is usually nocturnal and hibernates over the winter. Active among the branches of shrubs and trees, it feeds on flowers, fruits and insects.

First Class – Hedgehog Erinaceus europaeus
Average weight: 500–1200g Total length: 20–25cm

Britain’s only spiny mammal is found throughout the UK. Normally nocturnal, it snuffles about in gardens, farmland and woodland, feeding on worms, beetles and other small prey. It rolls into a tight ball when alarmed, and hibernates for five to six months over winter.