The Ueno Zoo has announced that female giant panda began showing signs of estrus on March 4. It will close the Panda House from March 7 for approximately two weeks until after the pandas mate. Last year the pair mated naturally and Shin Shin gave birth to a cub. Sadly it died a few days later.
Source: http://www.ueno-panda.jp/topics/detail.html?id=145
Pictures from http://mainichi-panda.jp/