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Mutualism, Mice and Mallards: Relationships of Ground Nesting
Birds in the Uplands of California


California Waterfowl Association, 3840 Rosin Court, Suite 200
Sacramento, CA 95834

Searches of upland habitat have revealed high densities and success of duck nests near major wetland regions of California. Northern harriers and short-eared owls were also found frequently nesting in the same habitats as were ducks. These species showed high variability in densities among years and geographic location. Previous studies have demonstrated that abundance of mice is extremely important for stimulating nesting in these species. In fields where nesting densities and success of harriers and owls were high, nest success of mallards exceeded 80% (Mayfield). Cinnamon teal, another nester in California uplands, did not nest where harriers were abundant. Northern harriers and to a lesser extent, short-eared owls are very aggressive defenders of territories around their nest sites. This trait may provide protection for mallards nesting close to owls and harriers. Northern harriers are effective predators of ducklings and have been observed feeding on young mallards that were more than half the size of adults (Class IIc). High nest success of mallards near harriers and owls would likely offset potential duckling losses, however. Adult cinnamon teal may choose to forego nesting next to harriers because they may be too small to deter attack. These observations suggest that predator-prey relationships may be complex and must be carefully considered before broad-scale imposition of predator control.
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