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Weights of Wild Mallard Anas platyrynchos, Gadwall A. strepera, and Blue-winged Teal A. discors During the Breeding Season

Introduction


Body weight is an important attribute of wild waterfowl, reflecting growth and development of young and general physical condition of adults. Waterfowl are most vulnerable before fledging; duckling mortality often ranges between 40 and 60% (Sergeant & Raveling in press). Increased weight tends to reduce the risk of mortality in several ways; heavier ducklings are less susceptible to some predators (Lack 1968), generally have greater body reserves to withstand food deprivation (Haramis et al. 1986), and can better tolerate weather extremes (Koskimies & Lahti 1964). Thus increased body weight may account for the lower mortality observed in older ducklings. Despite the evident importance of the topic, studies of growth in wild ducklings have been limited, probably because of the difficulty in capturing precocial young (Ricklefs 1973).

Body weight and physical condition influence the breeding biology of adult ducks. Heavier females tend to lay larger clutches (Krapu 1981, Cowardin et al. 1985) and renest more readily after losing a clutch (Cowardin et al. 1985, Swanson et a1. 1986). Furthermore, higher body weights have been associated with greater survival probabilities (Haramis et al. 1986, Pollock et al. 1989). The objectives of this paper are as follows:

  1. To describe the patterns of growth in weight of wild Mallard Anas platyrhynchos, Gadwall Anas strepera, and Blue-winged Teal Anas discors ducklings.
  2. To examine patterns of weight change of adult ducks during the breeding season.
  3. To relate duckling growth and adult weight to environmental conditions.
Unlike many previous studies of weights of ducklings and adult ducks, this one relied on wild, not captive, birds.
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