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

Waterfowl Use of Nesting Islands and Structures in Phillips County, Montana

Dwain M. Prellwitz1
Bureau of Land Management
Glasgow, Montana 59230

Joe Ball and Susan Ball
Montana Cooperative Wildlife Research Unit
University of Montana
Missoula, Montana 59812

We searched 2248 waterfowl nesting islands and structures on stockponds and natural wetlands after the Canada goose (Branta canadensis) nesting seasons during 1983-1987. Islands were on Public Lands administered by the Bureau of Land Management's (BLM) Phillips Resource Area in north central Montana. BLM has constructed nesting islands and structures since the 1960's, but the majority (78%) of 1018 islands and structures were built in the 1980's. Islands and structures were searched primarily for estimating waterfowl use and production and for scheduling maintenance, but data were also recorded for other parameters.

All known islands were searched once during May through July in 1983 and 1984, whereas a 20% random sample was searched in each of 1985, 1986 and 1987. Islands with active Canada goose and/or canvasback (Aythya valisineria) nests were revisited for determining nest success. Data were recorded for island type, surface area of water, age of island, number of islands on each wetland, longevity of security water through the nesting season, need for maintenance, vegetative canopy coverage, presence of waterfowl broods, and status of each nest located, for each island searched.

Canada goose nest success was 84.7% for the period, with a range from 75.2% in 1984 to 95.9% in 1987. Abandonment due to spring snow storms was the greatest cause of nest failure. Geese nested on 35% of the islands and structures in 1987, but only 9.3% of the islands were used in 1984, the driest year of the study. Goose production ranged from a low of 0.4 goslings per island constructed (1984) to 1.9 goslings per island constructed (1987).

Duck use of islands ranged from a low of 1% in 1985 to 41% in 1987. Nest success was 76.9%, with a range from 50% in 1984 to 79.2% in 1983. Puddle duck nests comprised 58% of the duck nests found, whereas diving ducks accounted for 42%. Primary nesting species were mallard (Anas platyrhynchos), lesser scaup (Aythya affinis), redhead (Aythya americana), northern pintail (Anas acuta), canvasback, northern shoveler (Anas clypeata), and American wigeon (Anas americana).

Drought in the early 1980's plus a high rate of island construction accounted for low rates of island use during 1983-1985. Improved water conditions in 1986 and 1987 increased island use by nesting waterfowl as well as by nongame birds. Slightly more than half of the islands and structures contained at least one bird nest in 1987.

1Present address: Bowdoin National Wildlife Refuge, Malta, MT 59538
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