Possible breeding of Sakhalin Grasshopper Warblers Locustella aminicola in Aomori Prefecture based on song analysis

Abstract

The Sakhalin Grasshopper Warbler Locustella aminicola is a well-known summer visitor which breeds in Hokkaidō. However, in late July 2023, several males were observed and recorded singing at Shiriya-zaki (Cape Shiriya) on the Shimokita Peninsula, in northern Aomori Prefecture (northernmost Honshu). Sound spectrograms of songs were analyzed and classified to song types by patterns of fluctuations in the frequency of each note and in intervals between each note in one song. Mapping of multiple individuals singing simultaneously and individual identification by song repertoires suggest that at least six males sang at nine different points. This is the first report of possible breeding area in Honshu.