The Social Organization of a Mallard Population in Northern Iowa

Field: Agricultural and Biological Sciences (Life Sciences)

Twenty-two hen and 134 drake mallards were marked during a 2-year study of mallard (Anas platyrhynchos) breeding activity on Ventura Marsh in north-central Iowa. During April, sex ratios of mallards observed on breeding areas (54% drakes) were lower than those observed in fields or on open water areas (58% drakes). Numbers of mallards observed declined after the initial influx, and remained relatively constant throughout the breeding season. The number of breeding mallards appeared to be limited by pursuit flights. Sixty-four marked drakes, observed at least once with a hen spent an average of 17.6 days on the marsh whereas 70 drakes, not seen with hens averaged 1.3 days on the area. There was a continual turnover of lone drakes on the study area throughout the breeding season. The nests of 22 marked hens were destroyed between day 10 and 17 of incubation. Four of the hens left the study area, 3 remained but did not remate, and 15 remated. Of 11 identified rematings, 8 hens (73% ) returned to their original drake and 3 (27%) changed drakes after losing their nest. J. WILDL. MANAGE. 42(1):72-80 The social organization of mallard breeding populations is not clearly understood. Studies concerning courtship behavior, interaction between pairs, and nesting provide a base for understanding mallard mate selection and production. The pair is fundamental to mallard reproduction. Weidman and Darley (1971) reviewed the range of attitudes among investigators concerning the role of the mallard male and female in display and courtship. They concluded that the female is essential in directing display and that social display promotes pair formation, which occurs for the most part before spring migration (Hawkins in Hochbaum 1944:121; Weller 1965:227). Hochbaum (1944:16) and Sowls (1955:21) reflected the general acceptance by biologists that most mallards are paired upon arrival at spring breeding areas. Lebret (1961:105) defined a hen and drake as paired when they maintained close proximity when together and when the drake defended the female from other mallards. Pair interaction in the form of pursuit flights (3-bird flights) was described by Dzubin (1957), McKinney (1965) and Titman (1973). Pursuit and avoidance were believed responsible for the spacing of breeding pairs (Dzubin 1969a). The ultimate consequence of spacing appears to be a lessened competition for breeding requisites and dispersion of nests as an antipredator mechanism. Those pairs unable to enter a breeding system may attempt to est elsewhere, delay the breeding effort, or molt. During the reproductive effort, drakes were observed with hens on breeding areas throughout the laying period and for an average of 8 days into incubation (Lebret 1961:127). Dzubin (1955:286) reported drakes present in the vicinity of nests until day 14 of incubation. Unless the nest is destroyed or abandoned, the hen continues incubating until the eggs hatch. Nest destruction, which appears to be a limiting factor in the annual production of mallards, was reported by Dzubin and Gollop (1972) to 1 Support provided by Iowa Conservation Commission P-R Project W-115-R-2 and the Michigan Agricultural Experiment Station; Journal Article Number 7689. 2 Present address: Missouri Department of Conservation, Fish and Wildlife Research Center, Columbia 65201. 72 J. Wildl. Manage. 42(1):1978 This content downloaded from 157.55.39.215 on Tue, 30 Aug 2016 05:35:26 UTC All use subject to http://about.jstor.org/terms MALLARD SOCIAL ORGANIZATION * Humburg et al. 73 range from 22 to 73 percent, depending upon the area studied, nesting cover condition, predator density, water level, weather, and human disturbance. Renesting, as high as 77 percent (Keith 1961:67), plays an important role in maintaining annual production in breeding mallard populations. A pair bond is necessary for successful culmination of egg laying and clutch incubation (Dzubin 1970), so hens losing nests probably will not renest without remating, even though they can lay fertile eggs up to 17 days after insemination (Elder and Weller 1954:501). Renesting hens could select a drake from a variety of sources; the original mate, a drake originally paired with a different female, or a previously unpaired drake. Although few data are available concerning the breeding activity of unpaired drakes, Titman (1973:41) observed marked unpaired males for a short time in localized areas on a breeding marsh. He speculated that there may be a selective advantage for an unpaired drake to be available for breeding with renesting hens. Elder and Weller (1954) suggested that unpaired drakes are essential to high productivity by supplying mates to renesting hens. In studying pintails (Anas acuta) Smith (1968) found that pursuit flights may often result in rape of the female, insuring fertilization. However, unpaired drakes could be harmful to production by harrassing nesting hens (Titman and Lowther 1975). Investigations by Bellrose (1961) revealed mallard sex ratios generally favor drakes and ranged from 68 to 233 drakes: 100 hens, depending upon latitude, season, and data collection method. The percentage of drake mallards appears to have increased since 1970 (Bellrose 1976:230). Some biologists have advocated harvest of the excess drakes. Dzubin (1970) suggested that harvest of surplus drakes may be biologically justified if (1) no difference exists in the time required for sexual maturity in both sexes, (2) surplus drakes have no significance in providing mates for renesting hens, and (3) harvest of hens would not parallel drake harvest. With the advent of the point system in waterfowl hunting regulations, which allows for the harvest of surplus drakes, controversy has arisen concerning the biological implication that increased drake harvest could have on mallard production. This study was designed to describe the structure and relationships between various components of a mallard breeding population on a breeding area. Specifically, the breeding activity of drake and hen mallards relative to the nesting cycle of unsuccessful nesting hens is described. We gratefully acknowledge the assistance of V. Wright with the project design, E. Peloquin and B. Batt for assistance with methods and data analysis, and G. Dudderar and D. Beaver for evaluating the final manuscript. Field assistance was provided by T. Willson, A. Woodward, R. Andrews, and