The time was right, and they were both sending signals that love was in the air.

But when Zoo Atlanta's giant panda Yang Yang approached the object of his affection late Sunday, fellow panda Lun Lun rebuffed his attempts.

File photo (ENLARGE)

Lun Lun, right, chomps on bamboo with her baby Mei Lan in a photo taken earlier this year.

LIVING Latest Headlines: Secluded Georgia refuge takes in misfit gorillas  Decatur First Baptist keeps woman in the pulpit  Zoo Atlanta's gorillas include numerous old-timers  Atlanta conference examines institution of marriage  World's oldest polar bear dies at Canadian zoo  • More Living Stories • Living photo galleries • Georgia Aquarium news and photos • Zoo Atlanta news and photos

Actually, she wasn't quite that nice about it, and made it clear that while cuddly-looking, she is indeed a bear.

"She wasn't even letting him get near her," said Dr. Rebecca Snyder, the zoo's curator of carnivores. "She was very aggressive."

Such was the challenge zoo officials faced over the weekend and early this week in getting the pair to mate naturally while Lun Lun was ovulating. In the end, the zoo went with a no-so natural process, artificially inseminating Lun Lun twice with Yang Yang's semen.

"Artificial insemination is a successful tool to increase the population when natural mating does not occur," said Dr. Maria Crane, the zoo's vice president of animal health.

If successful, it wouldn't be the first time. Lun Lun gave birth in September 2006 to Mei Lan after artificial insemination.

For months, zoo keepers have been monitoring Lun Lun and Yang Yang. A Barry White record and scented candles might put humans in the mood, but it's a little more complicated for pandas.

First, there is a much smaller window for the mating season. That window is open only once a year — in the spring. After a female panda's egg is released during ovulation, fertilization has to happen within 24 hours, Crane said.

Second, in the wild, the female would have several suitors who would fight for her affections, thereby building up their testosterone for the mating ritual.

Both Lun Lun and Yang Yang showed all (well, almost all) the expected behaviors and signs that happen in a mating ritual, said Snyder.

They were making mating calls — bleating sounds — and their urine showed elevated levels of estrogen and testosterone, Snyder said. Lun Lun also used her tail to leave her scent, while Yang Yang marked his territory, spent more time walking and less time eating.

Years ago, in an attempt to get Yang Yang more accustomed to affection in captivity and promote breeding, the zoo had him spend more time with his mother after his birth, Snyder said. Unfortunately, that hasn't helped his relationship with Lun Lun.

On Sunday, two hours after the first failed attempt for the two to mate naturally, zoo doctors lightly anesthetized the pair, extracted semen from Yang Yang and artificially inseminated it into Lun Lun.

The next morning, they hoped that perhaps nature would still take its course. Having recovered from the anesthesia, Yang Yang approached Lun Lun one more time. But despite Monday's picture-perfect sunny skies — Lun Lun said no.

Snyder mostly faults inexperience.

"They have not mated before," she explained.

So Lun Lun was then artificially inseminated a second time.

For the next two months, zoo doctors will monitor Lun Lun's estrogen and progesterone, Crane said. They also will do ultrasounds. Still, it may be awhile before they know for certain whether she is pregnant because of fetus will be smaller than the "stick of butter."