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A 3-year study was conducted in Manitoba and in Michigan to test the effects of age, captivity, and geographic origin on several reproductive parameters of captive mallards (Anas platyrhynchos). The Fl generation had a longer breeding period and higher egg fertility than did the P1 generation. First-year breeders were lighter in weight at the onset of the breeding season, but no difference was found between their reproductive potential and that of older birds. Michigan mallards nested almost 4 days earlier than did the Manitoba birds in both locations. This suggested that regional variation can occur even in species with a mating system such as the mallard. Egg weight was not related to the weight of the female. Egg weight of individual females differed significantly and a high degree of repeatability was determined for this trait. Egg fertility decreased in renest clutches. Management implications of the results are discussed. J. WILDL. MANAGE. 42(4):834-842 The mallard has holarctic distribution and there are many mallard-derived species in both the northern and southern hemispheres. It is the progenitor of all 17 breeds of domestic duck except the muscovy (Cairina moschata) (Delacour 1964:161-165). In North America 6 subspecies have evolved from the original mallard stock (Johnsgard 1961). Prince et al. (1970) demonstrated significant changes in several reproductive traits between F1 and F2 generations within a flock of semidomesticated mallards. The first part of this study examined the hypothesis that measurable change in traits would occur between the P1 and F1 generation in captive mallards. Recent reviews indicate that many waterfowl species may have reduced breeding potential during the first years of life (Weller 1964, Lack 1966, 1968, Trauger 1971). Although geese, swans, and some sea ducks do not nest in the first 2 to 4 potential breeding seasons, ducks of the Anatini breed in the first year. Younger breeders may not be as successful as older birds. Some waterfowl may breed at a younger age in captivity (Weller 1964:40, Lack 1968:237) suggesting that the captive environment is probably free of many of the environmental restraints affecting success in the wild. Analysis of age-related reproductive characteristics of captive birds should provide insight into whether or not effects observed in the field are due to environmental factors, or due to the breeding strategy of the species. The reproductive parameters of first-year breeders and a mixed agegroup of older birds were compared in this study. Hochbaum (1960:239), Mayr (1963: 189), and Johnsgard (1968:72) considered most migratory waterfowl to have a panmictic mating system thereby negating the opportunity for regional differentiation of gene frequencies. The third part of the study was designed to test the hypothesis that there is no regional variation in mallard breeding schedule. The method of study here was to analyze the breeding response of mallards from 2 distinct parts of the range while the respective groups were confined at the same locality. Gould and Johnston (1972:474) 1 Michigan Agricultural Experiment Station Journal Article No. 8008. 834 J. Wildl. Manage. 42(4):1978 This content downloaded from 157.55.39.213 on Sat, 02 Jul 2016 04:57:26 UTC All use subject to http://about.jstor.org/terms MALLARD REPRODUCTIVE PARAMETERSBatt and Prince 835 have pointed out that this procedure is most useful in assigning cause in studies of geographic variation and Miller (1960) inferred the same for studies of breeding schedule adaptation. We thank D. L. Beaver and W. Conley for their comments on an earlier draft of this paper. J. L. Gill gave valuable advice on statistical procedures. D. Jelinski, R. Kaminski, K. Stromborg, and C. Savage provided invaluable technical assistance. We sincerely acknowledge the cooperation of Pete Ward. This study was financed through the Delta Waterfowl Research Station by the North American Wildlife Foundation, the Wildlife Management Institute, and the Ducks Unlimited Foundation. In Michigan it was supported by the Department of Fisheries and Wildlife and the Agricultural Experiment Station of Michigan State University. METHODS AND MATERIALS Breeding stock were reared from eggs collected from the wild in 2 locations; the southern lower peninsula of Michigan and south central Manitoba. The eggs were hatched, and birds reared and maintained using standard procedures (Ward and Batt 1972) at the Delta Waterfowl Research Station (50?11'N, 98'19'W) and at the Michigan State University Wildlife Research Facility (42'42'N, 84?25'W). In August of 1972, 4-5-week-old ducklings were exchanged by air transport between the 2 research stations. In Manitoba the birds were overwintered indoors while in Michigan they were kept outdoors. In each case they were kept as a flock and were exposed only to natural daylight. At Delta 2 additional groups of birds were available for study: (1) birds that had been reared and held during previous years, and (2) progeny of these birds. The birds were randomly paired in April 1973 and these same pairs were placed back together from the winter flock in April of 1974 and 1975. Groups of different ages or origins were not mixed. Body weights were taken on the day the birds were placed outside in 1973 and 1975. All birds were kept flightless during the breeding season. In the latter 2 years, males that had died were replaced but females were not. In 1973 approximately 20 pairs of each of 4 groups were formed: (1) Manitoba P1; (2) Manitoba Fl; (3) Manitoba P1, and (4) Michigan P1. In 1974 and 1975 all groups were considered to be experienced but, for convenience of reporting results, the names adult and novice were kept. In Michigan only the 2 groups were represented. Breeding pens were approximately 7 m2. Food was provided ad libitum from a metal feed dish. Each day new eggs were numbered and weighed then returned to the nest and left until laying had not occurred for 5 consecutive days. The eggs were then collected and the nesting material was replaced. This routine continued until all hens ceased nesting and had entered their prebasic molt. In Manitoba, the pen area was 1/2 water and 1/2 dry concrete base and each pen contained a nest box. In Michigan, the pen base was grass and, in 1973, water for swimming was not available while only straw was available for nesting. That arrangement proved inadequate so in 1974 and 1975 water for swimming and a nest box were provided. In both areas pairs were visually but not audibly isolated. In Michigan the birds were maintained to give data on initiation dates of the first nest. The remainder of the analyses refer to all 4 groups of birds held in Manitoba. Eggs were incubated artifically. UnJ. Wildl. Manage. 42(4):1978 This content downloaded from 157.55.39.213 on Sat, 02 Jul 2016 04:57:26 UTC All use subject to http://about.jstor.org/terms 836 MALLARD REPRODUCTIVE PARAMETERS* Batt and Prince Table 1. Comparison of reproductive parameters of first-year breeders and older birds for captive mallards in Manitoba, 1973.