I went birding after ringing with my friend. We saw Marsh Sandpiper at Ibaraki-pref. There were 2-30 individuals and almost all were first winter. We can saw the variation of the progression of molt. Individual 2, the progression of molt was first. So back and wing exhibited grey.
I tracked 1-2 minutes per individual and I found that one individual used particular foraging method. For example, one individual foraged with "pick up foraging" method first, it continue to forage with same method 2 minutes after. I think it is one of the example of Frequency-dependent selection. If almost all individual forage with "pick up", individuals foraging with "shaking neck" will become advantageous. Moreover, habituation to the particular foraging method is also adaptive. Collectively, I think it happens that specialization to the particular foraging method. However probably it is overstatement, Individuals select their foraging method depending on the case. After birding, I came up with that the foraging methods are different between windward and leeward. It hypothesis that "Upwelling" happens on rice field like on sea (What is Upwelling). Namely that, on the windward lot of feeds in mud will be appearing, on the leeward lot of feeds accumulates on surface. So maybe an individual selects "pick up" on windward and "shake neck" on leeward. Ruff pick up forager foraged on leeward and Long-billed Dowitcher shake neck forager foraged on windward. The distribution of birds and habitat selection are very interesting to me.