The Curlew Sandpiper is a summer/autumn visitor on coastal pools and estuaries. They have curved bill and they are slightly larger than a Dunlin. They have longer legs than a Dunlin, although they tend to wade in deeper water, so you can't see them (as in this case). The significant identification is the breeding plumage. They have deep coppery-red feathers which go very blotchy when they start to moult, which seems to be the case with this one. It was unfortunately a long way away (700 feet), so difficult to get a clear view.