The Effects of Cold on Mallard Embryos

Abstract

Environmental chambers were used to simulate ambient temperatures and lengths of exposure of mallard (Anss platyrhynchos) eggs in nests of wild birds in the vicinity of Delta, Manitoba. The effects of cold exposure on eggs prior to incubation as well as on eggs containing developing embryos were researched. Unincubated eggs withstood much longer exposure than those partially incubated, whereas the oldest embryos were most susceptible to cold. Increased hatchability resulted from cold treatments to both unincubated and partially incubated eggs. When incubated eggs were exposed to O C, males suffered greater mortality than females, and an unbalanced sex ratio resulted. Abnormal embryonic development resulting from exposure tol cold was observed. The degree of tolerance of the mallard embryo to cold appears sufficiently great to minimize lower hatches in the wild caused by cold alone. The effects of cold on waterfowl embryos are of particular importance in view of the low temperatures in the early spring environments, where most temperate zone dabbling ducks initiate nesting. Gottlieb ( 1963 ) devised a technique for determining the developmental age of Pekin ducks (A. p. domesticus ) by the elimination of older embroys through exposure to cold. Romanoff ( 1943) reported that lower than normal temperatures throughout the incubation period will lower the hatch in runner ducks ( A. p. domesticus ), and Prince et al. ( 1969 ) reported similar findings for mallards. The need for study of this aspect of the reproductive cycle was indicated by Sowls (1955:88-89) and by Hunt and Jahn ( 1966) . Our first experiment was designed to examine the effects of prolonged cold storage on the hatchaibility of fresh eggs, whereas the second experiment examined the effects of exposure to cold temperatures at 3-day intervals throughout the incubation period. The work was done at the 1 This project was financed by the University of Florida, the North American Wildlife Foundation, and the Wildlife Management Institute. Experiments were conducted at the Delta Waterfowl Research Station, Delta, Manitoba. 2 Present address: Delta Waterfowl Research Station, Delta, Manitoba. Delta Waterfowl Research Station in southcentral Manitoba, Canada. We thank H. A. Hochbaum and P. NVard of the Delta Waterfowl Research Station for providing facilities and equipment during this study. We are also indebted to H. H. Prince, Michigan State University, for guidance and suggestions at the onset of the study, and to A. E. Snart, University of Florida, who was a laboratory assistant during the 1968 field season. N. F. Godfrey assisted in caring for incubators and in rearing ducklings. J. Cornell, U11iversity of Florida, helped with the statistical analy-