What began as a mission to save the panda has become a wider quest to save the world's wildlife, and this year the World Wide Fund for Nature celebrates its 50th anniversary. To mark the occasion, the Royal Mail will launch a special set of Amazon stamps on Tuesday.

The stamps, printed on paper from trees grown in managed forests or recycled sources, feature the hyacinth macaw, the spider monkey, an Amazonian poison dart frog and the jaguar – symbols of a rainforest that conservationists are desperately trying to save.

In 1961, species such as pandas, polar bears, black rhinos and elephants were in danger of extinction. Determined to avert such disasters a group of conservationists including Sir Peter Scott and Sir Julian Huxley moved to act against an "orgy of thoughtless and needless destruction" of the world's wildlife. The result was the birth of the WWF.

The stakes are higher today than they were in 1961, with the charity taking on climate change. It will call on Britons to switch off their lights at 8.30pm next Saturday to mark Earth Hour.

To celebrate WWF's birthday, here are 50 things you may not know about the organisation.

1 It was founded in the Swiss town of Morges.

2 It was originally named the World Wildlife Fund – its name changed in 1986 to World Wide Fund for Nature, known as WWF.

3 A third of the world's known species – more than 18,000 – are endangered.

4 WWF's logo was inspired by Chi-Chi, London Zoo's giant panda.

5 It has been redesigned four times.

6 It employs more than 5,400 people worldwide.

7 Actor Leonardo DiCaprio donated £650,000 to save the tiger.

8 In the 1960s there were an estimated 5,000 polar bears. Now there are 25,000.

9 Its latest scheme to protect the jaguar aims to save one billion trees in the Amazon rainforest.

10 Nearly $10bn has been spent in more than 150 countries since 1961.

11 The Duke of Edinburgh is the President Emeritus of WWF.

12 In 1969, together with the Spanish government, it established the Coto Doñana National Park, one of the world's first wetland reserves.

13 Almost half (45 per cent) of WWF's total income comes from the Netherlands, the UK and the US.

14 One million regular supporters in 1981 have grown to a total of more than five million worldwide.

15 Elephant "flying squads" in India have been set up to prevent wild elephants from raiding crops.

16 Helped to bring about a ban on commercial whaling in 1986.

17 In 1990, WWF helped bring about an international ban on ivory trade.

18 It was the first conservation organisation invited to China in 1979 to assist in giant panda conservation.

19 China has committed to protect three million hectares of panda forest – an area the size of Belgium – by 2015.

20 The greater bamboo lemur – believed extinct – was rediscovered by WWF in Madagascar in 1986.

21 WWF helped to reintroduce the golden lion tamarin to Brazil's Atlantic forest.

22 The Royal Mint has produced a 50p coin for the 50th anniversary.

23 In 2002 WWF won a court battle against the World Wrestling Federation over the use of the initials WWF.

24 Sir David Attenborough was one of WWF UK's first trustees.

25 It estimates nearly half of the world's tropical forest has been lost over the past few decades.

26 Helped to create the Cockscomb Jaguar Preserve, Belize, home to one of the largest jaguar populations in Central America.

27 In 1992, a WWF team discovered a new species of large mammal – the saola, or vu quang ox – in Vietnam.

28 It helped to set up the Charles Darwin Foundation Research Station in the Galapagos Islands in 1962.

29 Giant pandas lost 50 per cent of their habitat between 1954 and 1989.

30 Of the 1,600 pandas left in the wild, only 980 live in protected reserves.

31 A fish with vampire fangs was among 145 new species discovered in the Greater Mekong region in 2009.

32 There are 3,200 tigers in the wild. WWF aims to double this by 2022.

33 If overfishing continues, the world's cod stocks will disappear in 15 years.

34 There are 1,300 projects run by WWF worldwide at any one time.

35 More than 350 new species were discovered in the eastern Himalayas between 1998 and 2008.

36 Numbers of Amur tigers in the wild have increased from an estimated 20-30 to 400.

37 About 120 new species have been discovered in Borneo's rainforest since 2007, including a frog without lungs.

38 More than 300,000 whales, dolphins and porpoises die in fishing nets annually.

39 WWF's Earth Hour reached more than a billion people in 2010.

40 Fewer than 20 white rhinos existed in South Africa in 1895 – now there are more than 17,000.

41 Numbers of black rhinos rose from 2,500 in 1993 to more than 4,100 today.

42 Nearly 2,000 whales are still hunted each year despite the ban.

43 1,200 new species were discovered in the Amazon in the past decade.

44 Coral reefs contain about 25 per cent of all known marine fish species.

45 At current rates of destruction, 60 per cent of the reefs will be destroyed in the next 30 years.

46 Sturgeon are more critically endangered than any other species.

47 Stocks of all species fished for food are predicted to collapse by 2048.

48 WWF's priorities for the next 50 years include tackling climate change and promoting sustainability.

49 The WWF estimates in the time it takes you to read this page another creature will have become extinct.