I remember many years ago a friend and I were walking a tract of prairie in the spring and came upon a duck nest with a couple dozen or so eggs it. “Dump nest’ my friend exclaimed.
Most everyone is familiar with cowbirds. They do not build nests, but rather lay their eggs in the nest of another bird species and let them do the rearing. It might surprise you, but there are a couple hundred bird species that build their own nests are also known to lay their eggs in the nest of another member of their same species. It occurs in grouse, swallows, grebes, waterfowl, and is fairly common in ducks, particularly cavity nesting ducks such as wood ducks.
Why would a female lay an egg in another bird’s nest? There are a variety of reasons. She may not have been able to find a suitable nesting site. Or perhaps here nest was disrupted or destroyed. Maybe she is unmated. And it may occasionally happen even if the hen has an active nest.
Laying an egg in another bird’s nest can result successful offspring without having to expend al that energy rearing the young, and could even result in more successful reproduction in the long run. But several dumped eggs (some dump nests may contain 40 or more eggs) may result in the “dumpee” female abandoning her nest. That is likely the type of nest we observed on our walk in the prairie.
Dump nesting is well known among cavity nesting ducks such as wood ducks. And it is has been shown that well-hidden nesting cavities experience less dumping than the more conspicuous ones, which may end up with so many eggs that the nest is abandoned. So it is advantageous for the female to find a well-hidden nesting cavity.
And there is an interesting twist to this. Wood duck nesting boxes are often put up to attract and help wood ducks, often times in areas with few natural cavities. But these structures are often placed in conspicuous locations which may not be as successful as if they were placed in less conspicuous places. As they say in business, location, location, location.