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One of my favorite species of waterfowl, and one of the most unusual, is the magpie goose (Anseranas semipalmata). I worked with these extraordinary creatures at Sylvan Heights Waterfowl Park (which I highly recommend that you visit if you’re ever travelling through North Carolina — it’s located off Interstate 95).
The magpie goose is the sole member of its genus and the sole member of the family — Anseranatidae — (and its closest relatives are probably the screamers). The magpie goose also has a bill that’s unusual among geese and other species of waterfowl, and its feet are barely webbed. They will also breed in trios, so “the social breeding unit is often polygamous and cooperative with both male and females caring for the young.” Furthermore, although they’re a precocial species, magpie geese, unlike other species of waterfowl, feed their own young and maintain brood nests. Another odd trait of the magpie goose is that, like the screamers, it’s not flightless during its molt. There’s also differences in juvenile growth between males and females. Via the Australian Journal of Zoology:
Sex differences in juvenile growth patterns are consistent with pronounced sexual dimorphism in adult body size (larger males), which is associated with an unusual polygynous mating system. Although smaller, females grow relatively faster than males, so that at a given age they have completed a greater proportion of the pre-fledging growth phase; wing growth is particularly advanced and females fly earlier. Slower development may increase mortality among juvenile males when family groups are forced to abandon drying swamps, and contribute to skewing of the sex ratio towards females. Larger hatchlings from large eggs tend to maintain a size advantage, at least until fledging.
More unusual facts about the magpie goose via Johnsgard (1965):
Two facts about magpie goose behavior are of special interest and may make this species unique in the Anatidae. The first is that from the time that they leave the nest, the downy young are fed directly by their parents in a bill-to-bill fashion (Fig. IF). The downy young have a loud, sibilant whistle which they utter with their orange bill open, and which seems to function as a food-begging call. They also forage for themselves, but much of their food is obtained by their parents, who bring up aquatic vegetation from under the water and allow the young to take it from their bills. Janet Kear (pers. comm.) has observed possible cases of parental feeding in Dendrocygna and Cygnus, but these forms apparently exhibit a much more rudimentary form of parental feeding than do the magpie geese. The second fact of special interest is that unlike those of some swan species, the magpie goose family does not return to the original nest at night for brooding; rather, both adults assist in building a “brood nest,” which is simply a pile of grass on which the young sleep or rest while being brooded by the mother. This brood nest is used until the young are about two weeks old, by which time they have largely abandoned parental feeding. A more detailed account of the development and the molts of the young has been published elsewhere (Johnsgard, 1961b).