Hormonal males

It's mating season for giant pandas - and right about now, males are at their peak for making cubs, a new study has found.

Scientists at the Smithsonian Conservation Biology Institute in Washington, D.C., have discovered that male pandas seem specially adapted to ramp up their sperm production in advance of female panda ovulation.

Panda captive breeding programs face the ongoing challenge that female pandas ovulate just once a year.

The new findings, published last week in the Biology of Reproduction journal, may improve the chances of preserving genetic diversity in an already small population that is under ever more pressure in the wild.

Getting into the mood

That female pandas are fertile for only a small window of time - 24 to 72 hours after yearly ovulation in spring - has long been known.

The Smithsonian study filled a gap in panda reproductive biology by determining that male pandas have a corresponding fertility cycle.

Measuring the testosterone, sperm count and testicle size of eight male adult pandas over three years, Smithsonian researchers at the Chengdu breeding base in China determined that the bears produce viable sperm for only about half the year.

"It is amazing that we did not previously understand the basic physiological changes occurring in the male giant panda during the breeding season and outside of it," said Copper Aitken-Palmer, lead author of the paper, in a Smithsonian Institute statement.

In male pandas, sperm production begins three to five months before female pandas go into heat, the study found. From mid-March to mid-April, male pandas reach their sexual peak.

At this time, male panda testes are up to three times larger than during non-fertile times, and they are also able to ejaculate three times as much sperm than at the beginning of their fertility cycle.

Male pandas have evolved with this cycle in order to be able to mate on-the-spot when female pandas enter their brief estrus, the scientists believe. During non-fertile seasons, male pandas save energy by producing no sperm at all.

The discovery could assist efforts to boost panda numbers. The species is notoriously difficult to breed in captivity and continues to face the danger of extinction.

Rare bears

Only about 1,600 of the black-and-white bears are left in the mountains of west-central China - although this estimate is up from the mere 1,000 thought to exist in the wild in the 1980s.

The solitary creatures can eat nine to 14 kilograms (20 to 30 pounds) of bamboo shoots every day.

Loss and fragmentation of bamboo forest habitat continues to threaten the panda bear. Its low rate of reproduction is another concern.

In addition, a separate study by the Smithsonian Conservation Biology Institute published last month found that pandas could lose more than half their remaining habitat to climate change by the year 2080.

The paper's author's expressed hope that new areas for the creatures might emerge during this period.

Groups including the World Wildlife Fund have been working to establish habitat reserves and biological corridors between isolated populations in China.

Aside from the 200-plus pandas living in captivity in China, a few dozen are scattered in zoos around the world.

Captive breeding programs are considered one hope in preserving the genetic diversity of the dwindling species. Such programs have met with limited success to date.

Pandas in Europe

Germany's panda bear, Bao Bao, lives alone in Berlin. In the early 1990s he was loaned to the London Zoo in a failed mating attempt. Efforts to inseminate another female at the Berlin Zoo were also fruitless.

Scientists and conservationists at the zoo in Edinburgh, Scotland, said panda offspring were unlikely this year, despite the promising behavior of its panda pair.

"Both were keen to mate, but their inexperience showed," said the zoo's research director Iain Valentine in a statement.

At the Madrid Zoo, artificial insemination in 2010 produced panda bear twins in the first successful effort of its kind outside of China.

Maria Delclaux, mammal curator at the Madrid Zoo, said the young pandas are a big draw for visitors. "It's the only place outside Asia where you can see twins," Delclaux told DW.

She said that although they put the male and female pandas together in an attempt to breed naturally, the male simply showed no interest. "It sometimes happens with pandas," Delclaux said.

A panda pair in Vienna has twice seen success, in 2007 and 2010 producing cubs naturally.

Eveline Dungl, a zoologist at the Schönbrunner Tiergarten in Vienna, said that the key to success was allowing the bears to communicate, and especially to perceive chemical messages in each other's scent.

"The pair has to harmonize," Dungl told DW from her experience observing the bears' behavior during the mating season.

In Dungl's view, the Smithsonian study confirmed observations of zoo staff familiar with the animals, for example that male panda bears' testes grow in size during the mating season.

Both Delclaux and Dungl hope that the study's results would be used to further captive breeding attempts.

"There are many factors to successful captivity," Dungl said.

Author: Sonya Angelica Diehn
Editor: Nathan Witkop