A pair of crested ibises gifted to Japan as a symbol of friendship by China arrived Wednesday amid warming relations between the two countries.

The donation by China of the internationally protected species comes as the Asian neighbors mark the 40th anniversary year of the signing of a bilateral peace and friendship treaty. It also comes ahead of Prime Minister Shinzo Abe's official visit to Beijing next week.

The pair are to be transferred from Narita airport to the Sado Japanese Crested Ibis Conservation Center in Niigata Prefecture.

The 2-year-old male and female ibises, named Lou Lou and Guan Guan, respectively, were born and raised in China's northern Shanxi province, according to the Environment Ministry.

Japanese-born ibises became extinct in 2003. Since then, Japan has been artificially breeding ibises by relying on the Chinese donations, the first of which was in 1999, and preparing them for reintroduction into the wild.

Since 2008, Japan has been releasing the ibises on Sado Island. The population there is now estimated to be over 350.

During his visit to Tokyo in May, Chinese Premier Li Keqiang agreed to provide more of the endangered birds to Japan, the first such transfer since November 2007.

In 2011, China's then-Premier Wen Jiabao expressed Beijing's intention to offer ibises to Japan, but the plan was shelved after a diplomatic dispute escalated in the wake of the Japanese government's decision a year later to put the Senkaku Islands in the East China Sea under state control.

Although China continues to claim the uninhabited islands, which it calls Diaoyu, ties between Tokyo and Beijing have been gradually improving.