Hong Kong's two giant pandas have failed to mate naturally, prolonging eight years of struggling to reproduce and leaving hopes of a city-born cub resting on artificial insemination.
The news came weeks after Matthias Li Sing-chung, CEO of Ocean Park, where the pair live, said the theme park and mainland experts were discussing whether to transfer them to their native Sichuan province if they failed to conceive again this season.
In a statement, the Aberdeen attraction concluded the cuddly duo's brief mating season with disappointing news for panda fans.
"During the three-day mating period, Ying Ying and Le Le were together for eight natural mating opportunities but all their attempts appeared unsuccessful," Michael Boos, the park's executive director for zoological operations and conservation, said.
To increase the chances of conception, Boos said, three rounds of artificial insemination were conducted on Ying Ying with Le Le's semen during the female's peak fertility period, which happened over a period of 24 to 72 hours.
"If successful, signs of pregnancy, including fluctuations in hormonal levels and behavioural changes may be observed as early as late June, though there is always a chance that she could experience a pseudopregnancy," said Ling Shan Shan, head of scientific research and animal management at the China Conservation and Research Centre for the Giant Panda in Wolong, near Chengdu.
Female pandas can only get pregnant during two to three days each year, usually between February and May.
While the gestation period for giant pandas is between 72 and 324 days, their pregnancies can only be confirmed by ultrasound scan 14 to 17 days before birth at the earliest, the park added.
Ying Ying and Le Le, both 13 years old, were presented to Hong Kong in 2007 as a gift from the central government to commemorate the 10th anniversary of the city's handover from the British. Their first mating season was in 2011, when they were five years old.
Despite an extensive breeding programme set up for the pair, they have been unable to have a baby. Ying Ying suffered a miscarriage in 2015, and subsequently had three phantom pregnancies.
Last month, Sichuan's Forestry and Grassland Administration welcomed the idea of relocating the pair back to breed in their birthplace, which would offer more potential mates. There are 451 captive pandas in the province.
Ocean Park's panda attraction Giant Panda Adventure, which was closed on Sunday for the pandas to breed, reopened on Wednesday.
This article was first published in South China Morning Post.