FERRUGONIUS DUCK overnights it and then gets spooked and disappears

Located the female-type FERRUGINOUS DUCK at Linford Lake at 8.20am in a small group of Pochard and Tufted Duck, from the Far Hide near the far bank by corner of lake near the mill. Observed for 5 minutes when the whole group was spooked. Unable to see in which direction it flew. Spent a further 30 minutes without success. Went to the Near Hide to search but without success again! Also present 2 Common Redshanks and 2 Oystercatchers (Mal McGar)