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

Elevated Nest Structures for Canada Geese in Northwestern Montana

Dennis L. Mackey and William C. Matthews, Jr.
Confederated Salish and Kootenai Tribes
P.O. Box 278 Pablo, MT 59855

I. J. Ball
Montana Cooperative Wildlife Research Unit
University of Montana
Missoula, MT 59812

High maintenance demands and objections based on aesthetics often hamper programs to increase waterfowl production using artificial nest structures. We installed 64 durable, unobtrusive nest structures for western Canada geese (Branta canadensis moffitti) along the Flathead River and tested the effectiveness of two durable nest materials, expanded shale landscaping rock and coarse bark chips. We also monitored numbers of nests and nest success in the structures and on islands to determine whether the structures actually increased the nesting population or merely redistributed pairs from island ground sites to nest structures. The total number of nests along the river increased from 53 in 1983, the first year structures were available, to 79 in 1987 (50% increase in 5 years). The nesting population appeared to stabilize at least temporarily in 1988 when 70% of the structures were being used by nesting geese. On the north half of the river where islands were rare, the total number of nests had increased from 4 to 27 after structures had been available for 5 years. Numbers of island ground nests on the entire study area declined significantly from 39 in 1983 to 26.3 annually in 1986-1988, but remained comparable to numbers present before structures were erected (1980=24, 1981=28, 1982=27). Average nest success among ground nests was 57%, with 39% of nests destroyed by predators. In nest structures, 89% of nests hatched and 7% were destroyed by predators. Nesting geese preferred bark to shale as nest material, but used shale in increasing numbers. The two nest materials did not differ significantly in nest success or hatching success of eggs in successful nests. During 1987 and 1988, when structures contained a mixture of bark and shale, occupancy of structures was ≥ 70% and nest success was > 90%. Shale nest material will last indefinitely, and the bark/shale mixture provides an acceptable nest material with little or no maintenance. Costs were estimated at $1.37 per gosling hatched. Managers employing artificial nest structures often seem to focus heavily on initial costs and, in doing so, may make unwise decisions relative to aesthetics, structure longevity, nest material durability, and maintenance requirements. Virtually all published accounts show that occupancy by geese increases gradually over several years. As a result, the longer that structures remain usable, the more cost-effective they become. Although geese may prefer soft nest materials such as straw or litter, they certainly do not need them. Furthermore, we suggest that the maintenance demands created by providing such traditional materials often represent a costly and unnecessary trade off. Future research and development work on waterfowl nest structures should emphasize the development of maintenance-free structures and nest materials. Many aesthetic objections can be minimized by careful selection of structure design and thoughtful standards for placement.

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