Mammals like the the otter and water vole use Norfolk's habitat for their homes
Norfolk Wildlife Trust has backed a new set of stamps which feature some of Norfolk's threatened mammals.
The otter, water vole, hedgehog and brown long-eared bat appear on the stamps and can be found in the county.
"It is brilliant that some of the species highlighted are really making a come back in Norfolk," said David North, education manager for Norfolk Wildlife Trust.
The stamps from Royal Mail will be available from Tuesday, 13 April 2010.
"Otters declined catastrophically throughout England in the late 1950s. In Norfolk by the 1970s, most traditional otter sites were deserted and whole river systems no longer supported any otters," said David.
"Today though, otters have returned to most of their former haunts in Norfolk.
"This conservation success story is the result of both better legal protection for otters and the banning of the pesticides which poisoned them."
You may not think of bats and hedgehogs as under threat but changes to their habitat have had an impact.
Changes to the environment caused by growth in roads and housing developments have made it hard for the once thriving garden regular.
"Species like hedgehog and brown long-eared bat are still widespread in Norfolk with larger gardens providing good sites, but both species are thought to be declining," said David.
Since the 1960s, bats have suffered due to disturbances to their breeding and hibernating places, as well as a lack of insects to eat because of increased pesticide use.
However, the introduction of legislation and bat boxes has helped the brown long-eared bat.
"Bats and their roosts are protected under the Wildlife and Countryside Act 1981 (as amended), which means it is an offence to block access to or damage or destroy a bat roost," said David.
"It is also an offence to kill, injure, disturb or handle a bat without a licence," he added.
Norfolk is an important stronghold for the water vole
The water vole has suffered massively due to changing environment and the introduction of the American mink - a predator.
"Norfolk is a particularly important area for the endangered water vole and Norfolk Wildlife Trust nature reserves, including Cley Marshes, Hickling Broad and Ranworth Broad are great places to look for this species," said David.
"The water vole has suffered the largest decline of any British mammal in recent years. Some estimates now place the population decline of water voles at 90%.
"Although water voles have declined in Norfolk, it remains a national stronghold with strong populations in the Broads, along the north Norfolk coast, in the Fens area and on the south Norfolk claylands."
Mammals is the Royal Mail's fourth Action for Species series and is available from Tuesday, 13 April 2010.