Laying Dates, Clutch Size and Egg Weight of Captive Mallards

This has led to several major reviews on the possible determinants of clutch size in birds (Cody 1971, Klomp 1970, von Haartman 1971). Waterfowl have posed particular problems because the chicks are precocial and do not require parental feeding, a factor that correlates with clutch size in many altricial species (Lack 1968a). Most hypotheses concerning the evolution of clutch size in waterfowl have implied that food supply for the female prior to laying and/or for the young is both a proximate and an ultimate determinant (Bengston 1971, Johnsgard 1973, Lack 1967, 1968a, 1968b, Ryder 1970). We report the results of an experiment in which single pairs of Mallards (Anas platyrhynchos) were held in identical breeding compartments and were thereby subjected to the same environmental cues for breeding. We determined laying dates, clutch sizes and egg weights for the same pairs of birds in 1973, 1974 and 1975. The responses of the birds in terms of the three parameters of nesting were considered to closely reflect interactions between genotype and environment. They should provide bases for evaluating proximate environmental effects in wild populations.