Zhang Zhihe, Chengdu Research Center for Panda Breeding
Kebi, one of the male giant pandas included in the 3-year study.
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updated 4/4/2012 5:55:46 PM ET 2012-04-04T21:55:46

The difficulty of getting pandas to mate in the wild and in captivity is legendary.

A new study sheds some light on just how tricky it can be. Giant panda males are reproductively viable for six or more months out of the year, but females are only in the mood for one to three days each year, according to a new study.

The new study takes a very close look at giant panda reproduction. It's the first to reveal male giant pandas' reproductive capacity over time. The research is published in the latest issue of Biology of Reproduction.

PHOTO: A Summer of Panda Pregnancies

In addition to the inherent problems of encountering a female during her short “ready and willing” mating period, a male giant panda must go on quite a journey.

“In order for the males to find females and breed successfully, they must travel large distances across difficult terrain,” lead author Copper Aitken-Palmer told Discovery News.

WATCH VIDEO: Watch as Mei Xiang and Tian Tian travel from China to the National Zoo.

Aitken-Palmer, head veterinarian at the Smithsonian Conservation Biology Institute, explained that the breeding season for all females lasts from February through May annually. Individual females then have one to three days of mating within that time frame. Prior research determined this but, until now, no one knew what was going on internally with the males.

For three years, Aitken-Palmer and her team evaluated the interrelated seasonal changes in male panda testosterone levels, sperm concentration, testes size, and reproductive behavior in eight male giant pandas at the Chengdu Base of Giant Panda Breeding in China.

The researchers found that, unlike females, reproductive fitness in male giant pandas changes over time, with sperm production already beginning three to five months before females enter estrus. During this period, the male panda’s testicles “become dramatically larger and their behaviors change,” Aitken-Palmer said. “The behaviors we see change are those associated with finding females, such as increased vocalizations and scent marking.”

Despite the seeming mismatch of moods, the male giant pandas are respectful of the females.

“The males are generally very good barometers of female receptivity, and will not breed with females outside of their receptive period,” co-author Rebecca Spindler, a reproductive physiologist at the Smithsonian National Zoological Park, told Discovery News.

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Although the period of reproductive viability differs greatly between the two sexes, the researchers believe the process is quite energy efficient, ensuring that males have enough sperm when the brief and unpredictable female panda estrus occurs.

While the hormonal changes driving male panda reproductive behavior occur over several months, Aitken-Palmer said that “during the breeding season, the males are already decreasing these hormones, behaviors and sperm production, resulting in an abrupt end to their reproductive potential around June.”

She added, “These changes allow for the male to successfully mate with as many females as possible, with as little energy expenditure as necessary.”

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A female giant panda produces about one to two cubs biannually, so strengthening the wild population is a difficult and slow process. As it stands, fewer than 1,600 giant pandas are left in the mountain forests of central China.

Another new study, authored by a different team of Smithsonian Conservation Biology Institute scientists, found that nearly 10,000 square miles of giant panda habitat will likely be lost by 2080 as climate change causes giant panda habitat systems to shift to higher elevations and latitudes. This means less than half of their already significantly decreased habitat is projected to be suitable in about 70 years.

Melissa Sanger is lead author of that paper, published in the International Journal of Ecology. Sanger, who is also an SCBI wildlife ecologist, and her team call for development of more protected areas that are aligned with climate predictions and for the creation of corridors to reduce fragmentation.

Captive breeding programs are also under way, such as hopes surrounding the Smithsonian National Zoo’s two giant pandas, Mei Xiang and Tian Tian. Although the two have bred early in the year for the past two years, so far Mei Xiang has not gone into estrus during 2012.

© 2012 Discovery Channel

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