Four species of leaf warbler breed in Japan ; Japanese leaf warbler, Sakhalin leaf-warbler, Eastern crowned warbler and Iijima's leaf warbler. Today I will write about the territorial behavior of Iijima's leaf warbler and ohters'. Identification of Iijima's is not easy, because it is resemble to Eastern crowned. But Iijima's has paler eye-stripe and narrower supercilium. And Iijima's doesn't have crown stripe. The song of Iijima's is characteristic so maybe we can identify easy. However one type of call "Hi" that is used for making an appeal somethings like foraging area, nest site or song post is similar to Red-flanked bluetail's call. I realized I cannot judge which is the species Iijima's or bluetail only by the call. Fortunately, other phrases of Iijima's call are not similar to other species' calls so we can identify Iijima's by call!
イイジマムシクイ (Phylloscopus ijimae) Iijima's leaf warbler 160503 Tokyo
Many Japanese birder maybe have never seen the breeding behavior of some leaf warblers. Because they breed at mountain but many people live at lowland. I had visited mountains many times so I could watch some kinds of behaviors. It is interesting that the processes of struggles between conspecific and interspecific are not different. At First, one individual invade other individual's territory with noisy flight. I named the flight as "Bee-flight" because invader emit a bee-like sounds with their wings. On the beginning of breeding season, invader sing a short song after "bee-flight". Territory owner often chase the invader with no-noise flight. Many time, this chase is so insistent. If owner won, he sing a loud songs near the border of territory. Occasionally, two individuals fight directory. On the middle of the breeding season, instead of invading two individuals sing each other at close range. On the situation of Iijima's they breeds in Japanese south islands that only one warbler species breeds. However the process is similar to mainland's one. When I visited a that island, I could see "bee-flight". Anyway it is known that clutch size of this species is smaller than other warblers breed in Japan. It's so interesting phenomenon and it has been revealed recently the reason why is the tropic birds' clutch is smaller than temperate's one. You should reed it. This weekend I will go a mountain and help a conservation research of Ptarmigan. I hope I can do my best.