Toronto Zoo panda showing signs of pregnancy

Congratulations may be soon for Er Shun, a six-year-old female panda on loan to Canada from China since March 2013.

A baby panda could be on the way, said Toronto Zoo officials, who have been keeping a close eye on Er Shun since she was artificially inseminated in April. The zoo released a video of Er Shun exhibiting "nesting" behavior earlier this month.

In the video, Er Shun is seen rubbing hay around her face and body, and rolling around to create a pile of hay. Besides showing possible nesting behavior, Dr. Gabriela Mastromonaco, the zoo's reproductive physiologist, told Xinhua on Tuesday, that Er Shun's progesterone levels are also higher than usual, which is generally a good sign.

"I think she's definitely opening up a lot more and she's becoming more confident in her play and whether that's just got to do with the weather or with the pregnancy, the high progesterone, we're not sure, but she's definitely looking really good," said Mastromonaco.

Giant pandas go through what is called delayed implantation and the gestation period is anywhere from 87 up to 186 days from the date of insemination, which makes it all the more difficult for zoo staff to know for sure if she's pregnant. Mastromonaco predicted that a cub could arrive as early as in August.

But she said it'll be impossible to confirm whether or not Er Shun is in fact pregnant until just 20 days before she gives birth.

"The tricky thing is that panda babies are born so small and immature that they don't really develop for a long period of time, " she said. "By the time we can actually pick them up on the ultrasound, because everything is so small, then they'll quickly grow and be born."

"By the time we actually see a sack and a little fetus, we're 20-25 days to birth," she added. "So it doesn't give us a lot of time to prepare, to kind of create the environment that she'll need to then mother and nurse the baby."

Er Shun was inseminated earlier this year after Da Mao, a five- year-old male panda who was slated to mate with her, was deemed " too sexually immature, and didn't show any interest in breeding." Since female giant pandas are only fertile for two to three days every year, experts quickly decided to do an artificial insemination with frozen semen flown in from China.

Mastromonaco said the small breeding window left them scrambling when they realized Da Mao just wasn't ready and that Er Shun was soon going to be in heat.

"She was probably one of the later pandas to come into heat, we quickly saw the estrogen levels rise, so we knew we were 10 days out, so it was a bit of a whirlwind at that point," she said. "In hindsight we could have missed it, but it all came together really well."

This is the first time the procedure has been attempted with a giant panda in Canada. Artificial insemination has a success rate of about 50 to 60 percent. Mastromonaco said that number might seem low to some, but the chances are actually pretty good when compared to other animals.

"When you think of some other species like the wild cats, tigers for example, your success rates for insemination are less than 10 percent," she said. "So compared to that with the pandas we're doing very well."

Zoo staff are now monitoring Er Shun daily for any unusual behavioral changes. They're also training her to take an ultrasound every week in hopes of confirming the news as soon as possible.