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Understanding the Dynamic Nature of Waterfowl Nest Predation:
A Novel Approach

STEVEN M. BYERS, ROBERT L. CRABTREE,
AND RONALD C. GATTI

McGraw Wildlife Foundation, P. 0. Box 9, Dundee, IL 60118;
Wildlife Research Institute, University of Idaho, Moscow, ID 88843;
Wisconsin Department of Natural Resources, 3911 Fish Hatchery Road,
Madison, WI 53711

The traditional management response to waterfowl nest predation has included predator removal or efforts to reduce the vulnerability of nests via dense nesting cover, elevated platforms, nesting islands, or fencing on fragments of upland nesting cover. However, a better understanding of the factors that influence nest predation within this landscape is needed before management strategies are formulated. We present published material and data that demonstrate nest predation may be influenced by the abundance of alternate prey. An early study of predator-prey relationships on an Iowa waterfowl nesting area suggested that nesting success of blue-wing teal (Anas discors) was buffered by the abundance of small mammals. In Utah, radio-marked striped skunks (Mephitis mephitis) demonstrated a shift in foraging strategy from a "widely-searching" to a "sit-and-wait" behavior that coincided with the increased availability of alternate prey later in the nesting season. That behavioral shift reduced the time skunks spent "widely-searching" and the probability of encountering nests. In Wisconsin, unpublished data indicated that waterfowl nesting success was positively related to the abundance of small mammals. In the high Arctic, where the food chain is relatively simple, the relationship between small mammal abundance and waterfowl nest success is more apparent. In Sweden, resident predators, including the stoat (Mustela erminea), red fox (Vulpes vulpes), and arctic fox (Alopex lagopus), shifted from their main prey of small mammals to alternate prey such as willow grouse (Lagopus lagopus) and then to oldsquaw (Clangula hyemalis) eggs and ducklings following a crash in small mammal populations. Similarly, large variations in the breeding success of brent geese (Branta bernicla) in the Soviet Union appear to have been closely linked over a 33-year period with the abundance of small mammals. Current management strategies in the prairie provinces which call for floristically depauperate stands of dense cover may actually reduce the quantity of alternate prey. Recent research has suggested that the spatial heterogeneity of grasslands affects small mammal populations. Specifically, increased heterogeneity of grasslands at the micro-habitat scale increased small mammal abundance, while a more diverse macro-habitat helped maintain stable populations. Unpublished data from Wisconsin support that contention; small mammals were more abundant in grasslands with forbs than grasslands without forbs. Further, other recent literature suggests that, for a given density of nests, nest predation may be reduced when nests are placed in sites that differ than when placed in sites which are similar. Management strategies which promote the heterogeneity of grasslands (e.g., native grassland restoration, light grazing, or controlled burning), and those strategies which delay nest initiation dates (e.g., controlled burning) should be further evaluated with regard to their effect on the abundance of alternate prey and nest success rates. Finally, published material and data from Wisconsin relative to concepts of island biogeography (e.g., distance to edge, edge effect) will be presented that demonstrate grassland nesting birds (including waterfowl) which nest in relatively small, fragmented grasslands are more vulnerable to nest predation.
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