Zoo keepers have begun a daily monitoring of the UK's giant panda couple as mating season approaches.
Edinburgh Zoo hopes Tian Tian and Yang Guang will produce a cub this year as the creatures start to show the tell-tale signs they are ready to breed.
There was disappointment last year when the pair did not mate and though Tian Tian was artificially inseminated she lost her foetus at late term.
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Panda reproduction is a notoriously tricky process, with females only ovulating once a year.
Iain Valentine from the Royal Zoological Society of Scotland (RZSS), which runs the zoo, said: "Tian Tian and Yang Guang are both in great health and condition and things are progressing nicely.
"The giant pandas are clearly showing an increased interest in one another, both pandas are fairly regularly scent marking now and we've also seen food intake increase in both pandas as they seek to drive their body weight up - all fantastic instinctive pre-breeding behaviours.
"Similar to last year, alongside our own experts, RZSS is working together with a number of global colleagues on the complex science that goes on behind the scenes. Natural mating will be attempted, likely followed by artificial insemination as recommended by our Chinese colleagues."
Tian Tian (Sweetie) and Yang Guang (Sunshine) are the first giant pandas to live in the UK for 17 years. They arrived on loan from China in December 2011 and will remain at Edinburgh Zoo for a decade.
Zoo bosses hoped the pair would mate naturally when she came into season but ruled out putting them together last April after assessing Tian Tian's behaviour.
She was inseminated using semen from Yang Guang and frozen semen from Bao Bao, a ''genetically important'' panda which died in Berlin Zoo the previous year.
Last week experts began the daily monitoring of Tian Tian's hormones which will signal when she is ready to breed. She will then have a period of just two to three days to get pregnant.
Mr Valentine said: "As of Christmas 2013, we again began to collect urine samples from Tian Tian. These are being picked up and analysed so that we can monitor two key hormones for breeding purposes - progesterone and oestrogen.
"We're currently just waiting for the all-important crossover of hormones in Tian Tian and then when this happens it means breeding is roughly seven to 14 days away. This week we moved to analysing Tian Tian's urine samples each day, so it's a case of watch and wait."
The panda gestation period is typically five months and one or two cubs will be born.
They enter the world blind, hairless and unable to move - making them entirely dependent on their mother for survival for their first weeks. Cubs feed on their mother's milk for the first year and start eating bamboo at around six months.