The nine rare ibises killed at an ibis preserve in Niigata Prefecture were attacked by a marten, the Environment Ministry said March 11.

Investigators found marten prints on snow leading to the 4,160-sq.-meter enclosure where the birds were kept at the Sado Japanese Crested Ibis Conservation Center.

The nine dead birds and another critically injured ibis were found March 10.

A veterinarian at the center said a trace near the ceiling of the cage suggests a small animal may have broken in from above.