I stayed home for my school exams so I could't go birding this week. Today's theme is Zitting cisticola I observed in Yonaguni island where the most west island in Japan. Zitting cisticola has a wide distribution in Palearctic. We can see this species in Japan normally. Yonaguni island is very small (30km^2), but there were many Zitting cisticolas.
Inhabiting only one subspecies in Japan. However In Yonagui, we can recognize the difference to mainland. One of the call is different. mainland population "tyu-" but in Yonaguni population "jyu-". When I heard the Yonaguni's call, I cannot judge the species.
I think Zitting cisticola is famous of polygamy. The evolution of breeding system of Zitting cisticola is progressed, it is considered from the evidence that female not sharing territory with her mate. It means that female fly to find feeds out of her mate's territory and invade neighbor male's territory. But Neighbor male don't mind if he find the invade female. The strong division of labor in breeding are seen in Zitting cisticola. Male make a lot of nest over 10 and song for invite female, and for copulation. Female bring up her chick in her own. Amazing information are published. Juvenile female join the breeding despite of soon after fledged!!! From adult female mate with 1 to 3 male in a breeding season and juvenile female join the breeding, the sex ratio tend to female. So the polygamy is formed.
I have a hypothesis that there are the difference in high density of mainland population to low density of Yonaguni population that threat song is used more common in mainland population. In song, low tril "tya tyatya" means threat, and very common in mainland. But I never been Yonaguni island in breeding season, so I want to confirm my hypothesis. This individual is female, judged from heavy streaked head and pale oral.