\Veights of 1,281 diving ducks of five species livetrapped on Seneca Lake, Ontario County New Tork, during January, February, and March of 1960, 1961, 1962, 196S, and 1971 are reported. Body weights drop significantly from early January through late February and March. The weight loss by redheads (Aythya americana) is emphasized with significant differences shown in the ll-year time span between 19160 and 1971. To make conjectures as to this difference, it is suggested that periods of zero to subzero temperatures occurring in 1971 and not in 1960 influenced weight loss. Also, dramatically different, and possibly less suitable, food resources dominating the aquatic environment of the lake in 1971 contributed to weight loss. After a flurry of attention given to publishing records of the body weights of birds in the 1920's and 1930's, little new information appeared. With some notable exceptions, waterfowl, largely neglected during the early period, have continued to be neglected. Leopold (1919) recorded weights of a number of species shot during the gunning seasons of 1917 and 1918 in the Rio Grande Valley near Albuquerque, New Mexico, and offered some generalizations regarding weight changes during fall and winter. Kortright ( 1942 ) serves with Bent ( 1923 ) as a good starting point for many aspects of the life histories of waterfowl. However, Bent offers little or nothing on body weight, and Kortright's data, although based on sizable numbers of individuals and divided on the basis of sex, do not indicate the time of year when the records were made nor any distinctions relative to age. Both of these are factors of significance. Dzubin (1959) recorded the weights of both adult and young canvasbacks (Aythya valisneria ) in Manitoba. Weller's ( 1957 ) work with redheads, most of it done at Delta \07aterfowl Research Station in south1 This is a contribution of the Federal Aid to Wildlife Restoration Program, New York PittmanRobertson Project W-39-R. ern Manitoba) offers good records of the body weights of this species. His data included weights of both sexes, adults and immatures, and spring, summer, and fall records. He also included weights of redheads from Utah and Michigan. Bellrose and Hawkins ( 1947 ) tabulated the average weights of ducks shot in the Illinois River Valley from 1938 through 1940 and included the weights of small numbers of redheads and canvasbacks and good samples of lesser scaup (Aythya affinis). Weights were categorized by age and sex. Longcore and Cornwell (1964) gave the weights of captive, immature canvasbacks and lesser scaups in conjunction with their study of the consumption of natural foods by these two species. In August 1962, near Fort Yukon, Alaska, approximately 10,000 flightless ducks were driven into a large trap on Ohtig Lake. One objective was to weigh large numbers of diving ducks. Yocom (1970) reported this remarkable effort and gave the weights of 355 adult diving ducks of seven species. The object of the present paper is to place on record the body weights of over 1,200 individual diving ducks of five species recorded during the winter period of January, February, and early March, and, in a number of cases, in late March. In 1960. weights were recorded as late as mid-April.