Timing of passage for Kamchatka Leaf Warblers during spring migration in Asahikawa, Hokkaido

Abstract

To determine the timing of the Kamchatka Leaf Warbler Phylloscopus examinandus migration, I conducted bird observations at a park in Asahikawa, Hokkaido, about five times a week during the spring migration period from 2017 to 2020. I found that the timing of the Kamchatka Leaf Warbler migration varied from year to year, but that warblers were most frequently recorded in late May and early June, and rarely in late June. Furthermore, the Japan Bird Research Association’s database were reviewed, and included records of 73 Kamchatka Leaf Warblers observed in Hokkaido from late May to mid-June. Because of the late migration by Kamchatka Leaf Warblers, it was difficult to judge whether the birds were observed while still on migration, or if they may have been in Hokkaido for breeding. Our result suggests that observation of Kamchatka Leaf Warblers after late June suggests a strong possibility of breeding, if observations are recorded in suitable breeding habitat. In such cases, an intensive investigation may confirm the presence of breeding.