A pair of giant pandas gifted by the central government to the Macao Special Administrative Region arrived in Macao in April. [Photo/Xinhua]

Worried about the low sex drive of giant pandas in zoos, scientists have tried many things to get them in the mood－including Viagra and "panda porn".

When all else failed, they've turned to artificial insemination to ensure the endangered black and white creatures have cubs.

On Tuesday, a study suggested the answer may be a lot simpler and, perhaps, more obvious: Let the pandas choose their own mates.

"Giant pandas paired with preferred partners have significantly higher copulation and birthrates," researchers said in the journal Nature Communications.

Generally, pandas in captivity are presented with a mate chosen by scientists based on the animals' genetic profiles. The goal is to minimize inbreeding and expand the DNA pool.

But the result is often frustrating, with the animals having to be coaxed through human intervention to show even the slightest sexual interest in whatever mate is paired with them.

A team from the United States and China ran a test at the China Conservation and Research Centre for the Giant Panda in Sichuan province to see if being allowed to choose their own partners might make a difference.

Male and female pandas were housed in enclosures with animals of the opposite sex on either side. They were allowed limited physical interaction with their neighbors through cage bars.

Scientists measured the animals' "mate preference behavior", which included different forms of playfulness and bond-forming, as well as sexual arousal.

Negative interactions could include signs of aggression or a mere lack of interest.

The animals were then introduced to each other for mating－with both preferred and non-preferred partners.

"The highest reproductive performance was seen when both males and females showed mutual preference," the researchers found.

The results should come as no big surprise. Ever since Charles Darwin published his theory of sexual selection in 1859, scientists have understood that mate selection is key to animal reproduction.

"Mate incompatibility can impede captive breeding programs by reducing reproductive rates," the study authors wrote. "It is therefore surprising that mate preferences have not figured more prominently in captive breeding programs."

"The future of conservation breeding will not take place in a test tube," they wrote.

Conservation group WWF estimates there are only about 1,600 pandas left in the wild in south-central China.