Eurasian Oystercatcher is not rare in Chiba pref against other prefs. Today I saw 17 Oystercatchers. 11 individuals were foraging on tideland and 6 individual were foraging & resting at rocky area. Rain today so it was not crowded with birder, so I could see they were not alarm during foraging. This pic is the scene that Oystercatcher came closely to me. I think It is important for good observation to not keep tripod high. I judge age as adult from legs and bill color, black-tone upperparts. But Iris is not fresh orange. Judged gender as female from long bill, dark point in eye. White of under the eyes is little reminiscence of European population.
ミヤコドリ成鳥♀ (Haematopus ostralegus) Ad female- Eurasian Oystercatcher 150810 Chiba
I never pay attention to the difference of moult progression of Oystercatcher. So I hypothesized that population seen in Chiba during summer is maybe not breeding therefore the progression of moult is fast. And today I went to confirm. I don't have the reference about mount of Eurasian Oystercatcher, but have about American Oystercatcher, Black Oystercatcher and Oystercatcher. The reference describes that adult American & Black Oystercatcher suspend moult during incubation, but I could not find the evidence of the suspended moult today. There is a possibility that Non-breeder don't suspend the moult because it is not necessary. The reference describes that the moult period of adult is Oct-Sep and young is Oct-May, too. Individual 1 of flying pic extent P10. P7-9 is not old, the paler white mirror of outer primarys is trait of Oystercatcher.
Left ; individual 4. Extent P9 and P10 old. Right ; Individual 5. Extent P10. Maybe average of progression of primary moult is as this individual. Many individual extent P10 an d not had old primary. Oystercatchers were not interfere with each others during foraging. I think it is attributed that Oystercatcher's foraging does not need speed because the main feeds are conchs, not clams (↔︎Sanderling), and not too close in forage(↔︎Egret) because conchs are distributed wide, not patch. And to steal conchs cooked by bill has a big cost. Maybe own foraging is more adaptive.