Criteria of Age of Incubated Mallard, Wood Duck, and Bob-White Quail Eggs

Abstract

IF field studies of birds are to continue to yield new findings that are qualitatively and quantitatively commensurate with the effort involved, techniques that yield new and more precise data must be constantly evolved. From more refined data, basic relationships that might otherwise be missed become apparent. This is particularly true in the case of the study of nesting birds, the eggs of which offer the possibility of more dynamic interpretation than is generally realized. With this in mind the writer developed a portable egg candler and a method of photographing incubated eggs with transmitted light. The primary purpose of candling eggs is, of course, to ascertain the age of the embryos, and through the examination of many nests, to accurately and efficiently determine the chronology of the nesting season. Candling also enables the investigator to anticipate the date of hatching so that return visits, if desired, can be made on the appropriate dates and the final outcome of the nest more readily determined. In the case of altricial species such as the Mourning Dove (Zenaidura macroura), the visit can be so timed that the young can be banded just before they leave the nest. Descriptions of a portable egg candler, an egg volumeter, and the technique of photographing incubated eggs with transmitted light have been presented elsewhere (Hanson, 1954, Journ. Wildl. Mgt., 18: in press). This report, primarily a continuation of the above report, presents photographs and notes on the developmental stages of three species: the Mallard (Arias platyrhynchos), Wood Duck (Aix sponsa), and Bob-white Quail (Colinus virginianus). These photographs should also be useful in determining the stage of development of eggs of other species whose incubation periods are similar. Photographs and notes on the incubation of Mourning Dove eggs will be presented later in conjunction with other studies of this species' nesting cycle. The writer is indebted to William E. Clark, Natural History Survey photographer, for his patient assistance in preparing the plates showing eggs-which were made from admittedly difficult negatives; and to Francis J. Kruidenier of the University of Illinois Department of Zoology for a critical and helpful reading of the manuscript.