At Guam and Rota, the NAMRU2 party failed to obtain any specimens but received reports of the presence of ducks on both islands. At Guam, reports were obtained of ducks of unknown species at a fallow rice paddy in August, 1944, and in a marsh near Agat on June 13, 1945. The presence of Japanese soldiers in the interior of Guam made it inadvisable to investigate marshes and swamps of the interior and the upper courses of streams. H. G. Hornbostel, as quoted by Phillips (1923:54), reported that ducks were found at Guam only in the Tolofofo River Valley. The NAMRU2 field parties investigated the lower reaches of this valley and found no evidence of the ducks. The upper part of this valley was used as an artillery range in 1945. Probably the firing of field guns was a disturbing influence to any birds that might have been there. If the ducks were on Guam at that time, they must have been secretive and restricted in their movements. At Rota, two ducks which might have been _A. oustaleti_ were seen by the NAMRU2 party on October 20, 1945, in a cultivated field. These recent reports indicate that the Marianas Mallard is secure for the present on the islands of Saipan and Tinian, but thoughtful conservation practices need to be placed in operation to insure its survival in the future. _Evolutionary history of Anas oustaleti._--In the past, most of the studies have pointed to a northern ancestry for _A. oustaleti_. Bryan (1941:187) has noted a relationship between _A. oustaleti_ and the Laysan Duck (_A. laysanensis_ Rothschild) and the Hawaiian Duck (_A. wyvilliana_ Sclater). Amadon (1943:1) suggests that these three species of ducks are rather recent derivatives of the Common Mallard (_A. platyrhynchos_) and postulates the evolution of _A. wyvilliana_ from migrants from North America. He further states that _A. laysanensis_ and _A. oustaleti_ may have been derived from _A. wyvilliana_ or may represent independent colonizations. Delacour and Mayr (1945:21) go a step further and make these forms subspecies of _A. platyrhynchos_, saying that they are "dull-colored editions" of the Common Mallard, that because of isolation they have become reduced in size and have lost many of the characteristics of their ancestors. Recently, however, Yamashina (1948) has concluded that the Marianas Mallard has evolved as the result of hybridization between the two species, _A. platyrhynchos_ and _A. poecilorhyncha_. His conclusions are based on a study of a large number of specimens, both museum skins and captive birds, in which he has been able to detect plumages of the _A. platyrhynchos_ type and of the _A. poecilorhyncha_ type (see Characters). He has noted specimens which have ninety percent of the characteristics of _A. platyrhynchos_ and ten percent of the _A. poecilorhyncha_ type. These percentages are reversed in specimens favoring the _A. poecilorhyncha_ type. In his series of skins he finds the _A. poecilorhyncha_ type of plumage most frequently,