Growth, Molts, and Plumages of the Gadwall

DESPITE the wealth of literature on waterfowl, the molts and plumages of few species have received adequate attention.Classical works such as those of Millais (1913), Phillips (1922-26), Schi#ler (1925-26), and Witherby et al. (1939) described the plumages of many species mainly from museum material.M.D. Pirnie (1928) studied various forms from both living birds and skins.The works of Sutton (1932), Salomonsen (1941, 1949), and Stresemann (1948) on the complicated molts of the Old Squaw (Clangula byemalls), indicate the need for similar detailed studies of other species.Schi#ler (1925), Witherby et al. (1939), and others included in their works descriptions of Gadwall (Anas strepera) plumages but none worked with living birds or with skins of birds of known ages and breeding histories.Using the fine facilities of the Delta Waterfowl Research Station at Delta, Manitoba from 1962-64, I was able to hatch, rear, and breed Gadwalls in captivity and study them in the wild.Here and in a concurrent study of breeding biology, I have attempted to correlate molts and plumages with environmental and physiological factors.PRENATAL AND POSTNATAL DEVELOPMENT The following discussion is based upon analysis of 42 embryos and 283 skins and repeated examination of about 250 live birds.Eggs from incomplete clutches and considered "fresh" were placed in incubators immediately after co]]ection.The incubators •vere usua]]y maintained at 99.5øF but were raised to 101øF when eggs were hatching.Relative humidity, though variable, was always kept high.Two embryos were preserved in 10 per cent formalin on each of 21 of the 23 days prior to hatching.None was stained and no slides were prepared.Nearly all of the 283 specimens were skinned from the back and made into flat skins, which allows examination of the papillae as we]] as the feathers.Of the total, 185 specimens were captives of known age (1 day to 27 months) and 98 were wild adults.Captive specimens dated 1 October