As visitors will understand when they tour the western part of the island in particular, Sri Lanka has one of the highest population densities in the world. Despite this handicap, the country has an extraordinarily rich and unique bio-diversity, in fact one of the highest in Asia. Within the confines of just 65,500 square kilometres inhabit well over 600 species of terrestrial vertebrates. For instance, there are 82 mammals (including elephant, leopard and bear), over 400 birds (the tally varies between ornithologists), 133 reptiles (including 80 snakes!), and 54 amphibians (the number rises as new species of frogs are being discovered).

This abundance of fauna is largely because in Sri Lanka's comparatively small area there are wide geological and climatic variations. Distribution appears to be affected by 7 vegetation zones, which were created due to differences in climate and, to some extent, soil. Studies have revealed that the fauna of Sri Lanka has a distinct composition, which reflects the island's geological history, climatic changes and vegetation form. The composition of Sri Lanka's fauna comprises three basic components: 

1. Relict species that date back to when Sri Lanka was part of the pre-historic super-continent known as Gondwanaland, which comprised what is now India, Australia, Antarctica and Madagascar, and shared similar fauna. Relict species include both the water monitor and land monitor (the largest representatives), the mountain lizard, and limbless skinks (which belong to a sub-family of reptiles found elsewhere only in Madagascar. 

2. Endemic species that became isolated when Sri Lanka was separated geologically from India about 12 million yeas ago. For instance, of Sri Lanka's 84 species of mammal, 10 are endemic (mostly rats and mice), while there are some 25 endemics among Sri Lanka's 400-plus avifauna, and 70 among the 133 reptiles. 

3. Immigrant species that entered Sri Lanka during the Ice Ages, which drove animals southwards from the Himalayas to warmer zones; and those that entered more recently during geological upthrusts. These immigrants date back about a million years, so they have only had time to give rise to new subspecies rather than to endemics. 

Among these species, unfortunately, are some that have become endangered. The World Conservation Union (formerly the IUCN) lists 43 animal species from Sri Lanka. Terrestrials include Sri Lanka's very own subspecies of Asian elephant, the Sri Lanka elephant, the Sri Lanka sloth bear, and the Sri Lanka leopard. Marine species are under particular threat. All five of Sri Lanka's turtle species - leathery turtle, hawksbill turtle, olive Ridley turtle, loggerhead turtle and green turtle - are listed, as is the Sri Lanka estuarine crocodile and the mysterious and elusive dugong. 

Visitors can see Sri Lanka's wildlife in a variety of ways. It is often best to try a national park if you wish to see Sri Lanka's 5 big mammal species - elephant, sloth bear, leopard, buffalo and wild boar. However, while this may be the most reliable way of viewing such creatures, it is by no means the only way. Wild elephants, for instance, can be seen at various well known locations at certain times. Outside Habarana just off the Trincomalee road at dusk is one. However, you don't have to go to parks or other far-off locations to view much of Sri Lanka's wildlife. Monkeys, mongooses and large lizards such as the water and land monitor, are just some of the exotic fauna that can often be seen in hotel gardens or in wild areas just off the beaten track.