Earth is in the grip of the "sixth great extinction crisis," say some scientists, with up to 2,000 species dying out each year.
These 11 great wildlife experiences could disappear within your lifetime.
1. Witnessing a great animal migration
Ancient rock art images of animals moving across the African savannah indicate that humans have been marveling at animal migrations for more than 20,000 years.
But poaching, agriculture, war and deforestation are encroaching on wildlife corridors around the world, placing these animal movements -- from Africa's wildebeest migration to the annual pilgrimage of North American bison -- under threat.
How to do it: GAdventures pairs good wildlife access with creature comforts on its Kenya Safari Experience tour (eight days from $3,490 per person; +1 888 800 4100), taking in Kenya's Lake Nakuru, Amboseli National Park and the Masai Mara, where Africa's wildebeest end their migration.
2. Coming eye-to-eye with a polar bear
While hunting is still allowed by some Arctic-dwelling native communities, it's climate change that poses the largest threat to polar bears.
Latest data from the International Union for the Conservation of Nature (IUCN) shows that eight of the 19 sub-populations of polar bear that roam the Arctic are in decline.
Scientists project that two-thirds of all polar bears could disappear by 2050.
Due to its southern exposure, Canada's Hudson Bay is one of the bear habitats most threatened by climate change -- increasing temperatures are forcing bears off the ice earlier each year.
How to do it: Churchill Wild (+1 866 846 945) is one of a handful of operators on the western shores of Hudson Bay that facilitate multi-day bear watching tours starting at around $3,000 per person.
3. Counting the stripes on a tiger
Tigers once roamed freely across Asia.
Today the world's most endangered big cats have disappeared from 90% of their historic range.
Just six of nine known tiger species are thought to remain, with an estimated 3,200 animals left in the wild.
While it's extremely rare to spot the elusive beasts in their natural habitat (the South China tiger, for example, hasn't been seen since the early 1970s), protected reserves in India and Nepal provide the best opportunities.
How to do it: Intrepid Travel offers a Chitwan Extension (four days from $430 per person; +1 800 970 7299) tour to Nepal's Chitwan National Park from Kathmandu.
Once a royal hunting reserve, Chitwan is home to elephant, rhino, crocodile, monkeys, deer and about 100 Bengal tigers.
4. Swimming amid live coral on Australia's Great Barrier Reef
The Great Barrier Reef, the world's largest reef system, is in peril.
Temperature fluctuations are primarily to blame for the disappearance of half its coral since 1985 and the Australian Institute of Marine Science predicts that less than a quarter could be left within a decade.
Following plans by the Australian government to industrialize parts of the reef, the World Heritage Committee passed a recommendation to consider listing the UNESCO site as "in danger" at a meeting in June 2014.
How to do it: Calypso Snorkel and Dive (+61 7 4099 6999) offers daily snorkeling and diving day trips to the reef from the Far North Queensland resort town of Port Douglas starting from $174 per person.
5. Tracking gorillas in the mist