Giant pandas Kai Kai and Jia Jia are preparing for their second shot at making a baby at the River Safari, following their failed attempt last year.

In the coming weeks, visitors may observe some intriguing courtship behaviour.

Male panda Kai Kai may bleat and scent-mark more frequently. He may also be spotted curling back his upper lip to sniff for pheromones to assess if his mate is ready to breed.

Meanwhile, Jia Jia may appear restless and bleat to attract Kai Kai when mating season arrives.

Kai Kai, nine, and Jia Jia, eight, mated for the first time last April, but natural mating and artificial insemination failed to work.

Giant pandas usually start to breed around the ages of five to seven years.

River Safari's team of vets and keepers now have a better understanding of the endangered bears' "notoriously complex reproduction process", Wildlife Reserves Singapore (WRS) said yesterday.

Kai Kai has been dutifully doing his daily "sexercise", or squat training, which is intended to strengthen his hind limbs and improve his stamina for the act.

Mating season for giant pandas is typically from February to May, and the couple, here on a 10-year loan from China, showed signs in January that their breeding season was starting.

The pair, which live separately, swapped exhibits and dens in January and February to allow them to smell the scent of another gender, which stimulates their mating instincts.

When keepers deem the pair ready, the pandas will be taken out of their respective exhibits for three days to allow natural mating in the dens.

During this time, visitors will not be able to see them.

Vets have collected Kai Kai's semen for artificial insemination should natural mating fail.

Dr Cheng Wen-Haur, chief life sciences officer at WRS, said: "Kai Kai and Jia Jia are the first giant pandas to live so close to the Equator and make an intriguing case study for researchers worldwide."

Melissa Lin