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Wood Duck (Aix sponsa)

Dump-Nests

While the normal brood size for wood ducks is 10 to 15, nests have been found to contain 30 eggs or more. These extra eggs are the result of "egg dumping" or intraspecific brood parasitism. Egg dumping occurs as a result of several factors, including nest predation and lack of available nest sites. Dumping occurs when a female wood duck, frequently a first-year breeder, follows another hen to hidden or scarce nest sites during the egg-laying period. The visiting bird is stimulated to lay eggs in the nest of the other hen. In the wild, this impulse is kept in check because wood ducks normally nest in isolated locations. Artificial nesting structures are often mistakenly erected close together and in highly visible locations, such as the center of a pond. This creates a situation where egg dumping is common, and overall reproductive success plummets. A hen whose nest is dumped with too many eggs may abandon it; the result is a huge amount of wasted reproductive effort. In a natural scenario, approximately 80 percent of eggs hatch. But where egg dumping is out of control, hatch rates may drop to as low as 10 percent. Because of this, it is critical to locate nest boxes in isolated locations as described above. If wood ducks are very rare in the area, it may be necessary to place boxes in open areas initially to encourage use, and then moving them to more secretive locations as the population increases.

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U.S. Department of the Interior | U.S. Geological Survey
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Menlo Park, CA [caww54]