Inuka, the first polar bear born in the tropics, has reached the grand old age of 27 -- well into his 70s in human years and two years older than the average lifespan of the creatures in captivity.

Zoo operator Wildlife Reserves Singapore said an April 3 examination revealed that the health of Inuka, who has been receiving treatment for arthritis for some time, had declined markedly.

The bear's activity levels have fallen over the past three months and he now prefers resting over interacting with his keepers, a statement said.

Inuka -- who was born at the zoo, and whose name means "Silent Stalker" in Inuit -- had been popular with visitors due to his playful antics in his pool enclosure.

But he has now cut back on swimming, his walking is stiffer, and he is less interested in his daily playing sessions involving traffic cones, balls and ice blocks embedded with his favourite food, the zoo said.

Veterinarians have ramped up the bear's daily care regimen and are administering medication, and a second health check will take place in late April.

"If results indicate that Inuka's welfare is not improving with these intensive treatments, his care team may have to make the very difficult decision not to allow him to recover from anaesthesia on humane and welfare grounds," said the statement.

Inuka's annual birthday celebration is one of the high points for visitors in the zoo's calendar, and last year he marked it with a special jelly and salmon cake.

As few as 22,000 polar bears are thought to remain in the wild, according to environmental group the WWF. Protection group the International Union for Conservation of Nature classifies them as vulnerable.

They are typically found in places with cold climates such as Greenland, and parts of Canada and Russia -- making Singapore, where daytime temperatures rarely dip below 25 degrees Celsius (77 Fahrenheit), an unusual location for the creatures to live.