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Locating and Managing Peninsulas for Nesting Ducks

Introduction

Production of upland-nesting ducks in the northern prairie region of North America is severely limited by high levels of predation. Studies conducted in this region during the last several decades revealed nest success rates of only 10 to 20%. Much of the predation is caused by medium-sized mammals including the red fox, striped skunk, raccoon, badger, and mink. These predators mainly destroy duck eggs but some species also take ducklings and incubating hens.

Many current management strategies seek to increase duck nest success by separating the nest from the predator. One way to provide this separation for upland-nesting ducks in the northern prairies is by managing peninsulas. Peninsulas in this paper are defined as projections of land into water, connected to the mainland at the base by an isthmus. Peninsulas provide good management sites because they are naturally attractive to nesting ducks and mammalian predator access is limited to a narrow isthmus. Predation can be greatly reduced at peninsulas by placing barriers on the isthmuses and removing predators that gain access.

Peninsula management has been most widely applied in the Prairie Pothole Region and to a lesser extent in the prairies and plains to the west (Figure 1). Managed peninsulas are usually natural parcels of land located in large wetlands. A variety of peninsula types can be managed including long narrow ones that project nearly across the wetland and broad ones that extend only a short distance into the wetland.

Duck nest success in the northern prairies averaged over 50% on peninsulas managed with predator barriers and predator control. On average, each managed peninsula contained 1.3 nests/acre (3.2 nests/ha). Duck nest success on unmanaged peninsulas was usually less than 15% with about 0.3 nests/acre (0.7 nests/ha).

Map of the United States and Canada with shaded portion showing the Prairie Pothole Region.

Figure 1. Peninsula management has been primarily applied in the Prairie Pothole Region of the United States and Canada and secondarily in the plains region to the west.

Common Nesting Species

Mallard, gadwall, and blue-winged teal are the primary nesting species attracted to managed peninsulas. These 3 species together compose about 75% of the ducks nesting on peninsulas. Northern pintail and lesser scaup each compose about another 10% of the nesting population. Although Canada geese, shorebirds, and colonial water birds seek islands as nesting sites they seldom nest on peninsulas.

Mallards, gadwalls, and blue-winged teal are the primary nesting species attracted to managed peninsulas. (photo by USFWS)

Management Options and Costs

Before initiating peninsula management, managers should visit each potential site, catalog its attributes, and determine its value for producing ducks (see section on Monitoring Peninsulas). The value of each peninsula for nesting ducks can be related to management costs in order to obtain the benefit-cost relationships of various sites. Although economic and engineering concerns must receive strong attention in the planning process, biological concerns must be given primary consideration. During the peninsula inventory process, managers should also consider evaluating island-nesting sites concurrently (Lokemoen and Messmer, 1993). Ultimately, the most cost-effective waterfowl management projects should be identified and developed first.

Predator barriers normally applied at peninsulas include electric fences and water-filled moats. Electric fences are the most cost-effective barrier because heavy equipment is not required for construction. In North Dakota, in the 1980s, the mean capital cost of constructing electric fences across peninsulas was $7,600 or about $7/foot. This compares to a mean capital cost of $207,000 for moats or about $100/foot. The cost of each fledged duck, including capital, maintenance, and predator trapping, was estimated at $12 for fenced sites and $62 for moated sites.

Photo of predator barrier with electric fence extending into a wetland.

Electric fences are the most cost-effective predator barrier on peninsulas, because heavy equipment is not required for construction. (photo by USFWS)

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