Abstract
Effectiveness of the species separation criteria was examined by observing 33 Marsh Tits Poecile palustris and 24 Willow Tits P. montanus from Hokkaido, Japan. As in Europe, the difference in bill marks was useful in Hokkaido, except when specimens still had their juvenile plumage. In fall-to-winter, a pale brown stain on the cheek area was also a useful criterion to identify Marsh Tits, but the “bib” was not useful. Reliability of all criteria based on feather color or length was low or none during breeding season and juvenile plumage. When mention about color of upper parts of both species, it should be necessary to consider about changes of feather color by wear and breach. Changes in feather color by wear and breach should be taken into consideration when color of upper parts are mentioned.
