By Brian L. Joynt, IWWR Biologist
Now what? After a hen has endured all sorts of advances from amorous drakes before finally selecting a mate, migrated hundreds of miles to the breeding grounds, helped her drake defend their chosen territory, explored countless spots before selecting a nest site, exposed herself to a dozen or more predators while laying or incubating, she now returns to her nest to find all her eggs have been eaten! What's a hen to do?
For many ducks, it's "if at first you don't succeed, try, try again." Many hens will "renest," that is, build another nest and lay another set of eggs to compensate for high rates of nest predation common on the breeding grounds. The new nest might be relatively close to the location of the hen's previous nest or a couple miles away in a completely different habitat.
If and when a hen renests are thought to be influenced by several factors. For example, the stage of progression of the nest at the time of its destruction is important. Ducks are "indeterminate layers." They will continue to lay eggs until their clutch is complete (as opposed to "determinate layers," which tend to lay a specific-sized clutch of eggs).
On any given day during laying, a hen's reproductive system holds six to seven partially developed eggs. One egg is typically laid each day until the clutch is complete, and then the partially developed eggs still inside the hen's reproductive system are reabsorbed.
If the nest is lost to a predator during the laying phase, the hen can immediately renest because she is still capable of readily producing additional eggs.
If a hen is in the incubation stage when her nest is lost, however, her "renest interval" is longer because she needs additional time to restart egg production. Nesting hens incubate about 20 to 22 hours each day.
While incubating, the hen must utilize her body reserves to maintain herself, and, doing so, she may lose from 25 to 35 percent of her body weight. If a hen loses her nest late in incubation, she will require a long renest interval because she has to rebuild her nutrient reserves before she can produce eggs again. Late in the season, she may not even have enough time to rebuild the necessary reserves.