Abstract
The breeding of the Ancient Auk, Synthliboramphus antipuus, has not hitherto been known from Hokkaido. In the springs of 1955 and 1956 the author found carcases of this bird on the Island Teuri, off the western coast of Hokkaido. Then at last a colony of the Ancient Auk with approximately 500 individuals has been found nesting on the steep cliff which consisted of pebbles and scanty humus. Above their nesting site there were about 500 Cerorhinca monocerata and below there were nesting about 1, 000 Larus carassirostris.
The ancient auk makes a simple dish like nest with a diameter of about 10 cm using gramineous grass, 30-50 cm deep in the natural crack. Two eggs are laid in June. The male and female incubate the eggs alternately. On the 1st of July, 1956, the chicks were seen being fed by the parent birds. The chicks leave the nest by the middle of July.
