Koopman K. (1986) Primary moult and weight changes of Ruffs in The Netherlands in relation to migrants. ARDEA 74 (1): 69-77

This paper gives an analysis of primary moult in relation to body-weight of 823 male and 304 female Ruffs caught in The Netherlands. In late June the first males start primary moult. Females start in early July. Almost all males present in The Netherlands in late summer start primary moult but only part of the females do so. This fits with observations on Ruffs arriving in their African wintering grounds in early autumn. Birds which complete the moult of their primaries in The Netherlands have finished by early October (males) or mid October (females) at the latest. The completion of primary moult takes about 72 days in both sexes. However, from early August onwards many Ruffs suspend the moult when the growth of five new primaries has been completed. Ruffs in active moult have lowest weights: 18G-190 g in males and 105-115 g in females. When primary moult is likely to be suspended (only one pinion growing), bodyweight increases. Birds in suspended moult are heaviest: males weigh 250 g and females 145 g. It is argued that Ruffs, which mainly winter in West Africa, reach their winter quarters in a non-stop flight of approximately 4500 km. After early September (females) or mid September (males), Ruffs may be unable to deposit sufficient fat reserves for a non-stop flight to West Africa. As Ruffs would be unable to complete primary moult before these dates, the moult is often suspended. The minority of males that do complete the primary moult in The Netherlands, probably also spends the winter here. They have sufficiently large reserves of fat to move to France in one flight, when a sudden period of frost would force them to do so.