Green Sandpiper

The green sandpiper is a somewhat plump wader with a dark greenish-brown back and wings, a greyish head and breast and otherwise white underparts. The back is spotted white, most heavily in breeding adults and less in winter and young birds. The legs and short bill are dark green. In flight the wings are dark above and below with a brilliant white rump, a feature that reliably separates it from the slightly smaller but similar solitary sandpiper of North America. Its flight call is a characteristic three-note whistle. (Wikipedia, general species account)

The species breeds across subarctic Europe and east across the Palearctic, and it is migratory, wintering in southern Europe, the Indian subcontinent, Southeast Asia and tropical Africa. Unlike most waders it nests in trees. It is very much a bird of fresh water and is often found at sites too restricted for other waders, which prefer a clear all-round view. It works steadily around the edges of its pond, picking small invertebrates off the mud, and is not gregarious, though small numbers sometimes gather. (Wikipedia, general species account)