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Ecology and Management of Islands, Peninsulas and Structures for Nesting Waterfowl

Dense Nesting of Gadwalls and Lesser Scaups on Jessie Lake, Alberta

Bruce Turner and Paul Pryor
Canadian Wildlife Service
Edmonton, Alta.

David Sharp
United States Fish and Wildlife Service
Minneapolis, Minn.

Ray Greenwood
United States Fish and Wildlife Service
Jamestown, N.D.

We studied island-nesting gadwalls (Anas strepera) and lesser scaups (Aythya affinis) on Jessie Lake in northeastern Alberta in 1985 and 1986. Several parameters of nesting biology were investigated and the impact of passive avian predator management was assessed. Gadwall and lesser scaup nests comprised 60% and 30% respectively of the 1449 nests which were found. Four plant communities were represented on the islands: trees (Populus tremuloides and Amelanchier alnifolia); bulrush (Scirpus spp.); shrubs (Symphoriocarpus occidentalis, Rosa spp., Ribes spp., and Rubus spp.) and grasses. Seventy-three percent of all nests were in shrubs where densities ranged from 290 to 333 gadwall nests/ha and from 80 to 117 lesser scaup nests/ha. Habitat preferences in order of decreasing attractiveness were shrubs, trees, bulrush and grasses for gadwalls and shrubs, bulrush, grass and trees for lesser scaups. Eighty-one percent of the gadwall and 79% of the lesser scaup incubated clutches contained the normal range of 7-14 eggs but intraspecific and interspecific egg-laying were common. The incidence of 15 or more eggs in incubated homogenous clutches was comparable for the two species: gadwall - 16% and lesser scaup - 15%. Nineteen percent of all gadwall nests contained eggs of other species while 24% of the lesser scaup nests were parasitized. Mean nest success was 74% for gadwalls and 70% for lesser scaups. Success was lower in parasitized and large clutches (>14 eggs) than in those which were homogenous and of normal size. Avian predation was the principal cause of nest failure in 1985 accounting for 54% of the total losses. Passive predator management in the winter of 1985-86 involving the removal of perch sites of the American crow (Corvus brachyrhynchos) and great horned owl (Bubo virginianus) reduced nest loss from 15% in 1985 to 10% in 1986, and the number of adults found dead by 59%. In the Alberta parkland natural islands which do not have trees tend to have high densities of nesting ducks. The many heavily-wooded natural islands in parkland areas afford an excellent management opportunity to duplicate the high productivity levels observed at Jessie Lake.
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