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Biology and Conservation of the Laysan Duck (Anas laysanensis)
Daniel W. Moulton and Milton W. Weller
Vol. 86, No. 2 (May, 1984), pp. 105-117
Published by: American Ornithological Society
Stable URL: http://www.jstor.org/stable/1367021
Page Count: 14
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A two-summer, mark-recapture study of Laysan Ducks (Anas laysanensis) resulted in a population estimate of 510 birds with over 90% of the birds marked. Individuals seemed long-lived with the low reproductive rate common to K-selected species. Nesting occurred in spring and early summer in spite of the subtropical climatic regime. Nests were mainly in clumps of grass (Eragrostis) and hatching success was low. Duckling mortality due to exposure was common during rainstorms, but no direct predation was noted. Pair-bond behavior resembled that of continental populations of Mallards (Anas platyrhynchos) but males tended to return to mates after brood-rearing or loss of brood or nest. Year-to-year mate switching occurred more than half the time, even when previous mates were alive. Males did not assist in care of the brood. During spring and summer, ducks of all ages fed heavily on invertebrates. Adult brine flies (Neoscatella sexnotata) on mud flats around the lake were the major food of ducks of all ages. Radio-marked pairs consistently used the same upland areas during the day. At night, most ducks moved to a lake on the island to feed, and to drink in communal areas at freshwater seeps. Feeding and drinking was dominantly crepuscular and nocturnal at the lake, but laying hens or hens with broods sometimes fed throughout the day as well. Conservation of the species requires monitoring of duck populations and habitat conditions, and surveillance for accidentally introduced predators such as rats. The lake is vital to the success of the species, and it is unlikely that a significant population could survive on terrestrial resources alone. Intensive management will be necessary only if blowing sands fill the lake, predators become established, or the vegetation is seriously damaged in some way.
The Condor © 1984 Cooper Ornithological Society