Two artificially incubated rock ptarmigan eggs have hatched in a government-backed breeding program, according to zoo officials in the city of Toyama.

It was the first time that eggs from captive-bred birds of the species, similar to pheasants and grouse, were artificially incubated and hatched in the government-backed breeding program, the officials said Sunday at the Toyama Municipal Family Park Zoo.

The two eggs that hatched were among 19 laid since late May.

The program is being undertaken by the Toyama zoo, Ueno Zoological Gardens in Tokyo and Omachi Alpine Museum in Nagano Prefecture, using 22 eggs collected from Mount Norikura on the border of Gifu and Nagano prefectures.

Rock ptarmigans, an endangered species designated as a special natural treasure, are found in Japan only in mountainous areas above an altitude of about 2,700 meters.

Their population is estimated to have been around 3,000 in the 1980s but numbers have fallen to less than 2,000 due partly to their vulnerability to natural enemies such as foxes and crows.