Hoogerheide C. & Hoogerheide J. (1958) Slagpenrui van de Bergeend, Tadorna tadorna L., in Artis. ARDEA 46 (3-4): 149-158

A moulting of wing feathers (primaries and secondaries), which make the birds unable to fly, was studied on 7 Shelducks (Tadorna tadorna L.) in the Amsterdam Zoological Garden 'Artis'. Estimation of the number of days on which the birds are helpless through lacking the use of their wings, varied between 25 and 31 days. For the drakes an average of 29 days and for the ducks 27 days. As an average specimen of the other primaries, the new third primary of every bird was measured weekly. The data thus obtained are shown in Table 1 and Fig. 1. As a first approximation we conclude that there exists a constant velocity of growth during at least 3 weeks after the time that the new feathers appear. We may estimate the average daily increase in length at 7 mm. The length of the full grown 3rd primary varied in the males from 21 to 22.5 cm, and in the females from 18.5 to 19.5 cm. We learned that the birds were able to fly long before their wing feathers had attained their full size. A drake could fly when his 3rd primary was only 17 cm long, and a duck when it was 16 cm long. The time that elapses between the throwing off of all primaries and secondaries and the reappearance of the new ones, is roughly estimated at about 3 days. The beginning of the wing moult in the birds was spread over a relatively long period of time. The earliest wing moult began on July 16th and the latest on August 27th. The three early moulting birds were drakes and the two latest ones were ducks. Age did not play a role in any aspect considered.