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.
Renesting behavior is different for each duck and goose species. For example, mallards and northern pintails are more likely to renest than are lesser scaup and gadwall, because mallards and pintails are early nesters. If their first nest fails, they usually still have time left to renest and have the brood gain flight before the end of the breeding and brood-rearing season.
Scaup and gadwall nest three to four weeks later than mallards and pintails, and they renest much less frequently. (Geese nesting in the far north rarely renest because they are subject to even greater time constraints imposed by a particularly short breeding season.)
Age also influences renesting. Older, more experienced hens are thought to arrive on the breeding grounds earlier and initiate a nest sooner than younger birds. Thus, older hens have a longer nesting season. Older birds are also more familiar with local food sources, which are critical in providing nutrients necessary for additional egg production.
Productive wetlands are vital for nesting hens because they provide most of the nutrients required for egg production. If wetlands are scarce due to drought or habitat loss, hens may have a more difficult time finding the necessary resources for renesting. Conversely, waterfowl are more likely to renest during years of high water levels or in years when summer precipitation improves or maintains wetland habitat.
Renesting helps waterfowl offset the effects of nest predation, but it does not guarantee success. Some hens may try to nest several times but will still be unsuccessful. On the other hand, some early-nesting mallards that lose their entire brood of ducklings shortly after hatch may renest, but this is rare.
Renesting comes at a cost. A mallard, for example, requires about 35 days to lay a clutch and incubate it to hatch. By late incubation, a hen is usually very reluctant to leave her nest. For the swift and alert predator, finding a duck nest can include a bunch of eggs and a duck dinner.
This reluctance to leave the nest also makes hens susceptible to being killed by haying and mowing equipment. The more time a hen spends nesting, the greater the probability will be that she will pay the ultimate sacrifice for a chance at hatching a clutch of eggs.
Renesting can be very important for waterfowl production. In many areas, few ducklings would be produced if hens gave up after only one nest attempt. Though the odds of successfully hatching a nest are usually low, the more nests that are attempted, the more nests that will hatch. So, for many hens, if at first you don't succeed, RENEST!
Even for hens that beat the odds and hatch a nest, the battle is far from over. Of the ducklings that hatch, 40 to 60 percent will not survive to reach flight age (approximately 55 to 65 days old).
Duckling mortality is most common during the first two weeks of life. The quality and quantity of wetlands, weather, and predator populations all influence duckling survival. Ducklings fall prey to many different predators, such as mink, turtles, fish, night herons, marsh hawks, gulls, and foxes.