Black-backed Wagtail Motacilla Alba Bird Eating Green Algae in Shallow Running Creek Water Flow at South Korea

white wagtail blackbacked wagtail bird eat algae water fresh stream white black backed alga running shore single walk wet wing behavior bill feed slow motion avian beak one ornithology plumage rock rocky animal brook color detail forage moss seaweed south korea closeup coast river stone fast flowing peck creek rapids alerted blackbacked wagtail