To maintain healthy waterfowl populations, two factors are especially important—nest success and survival of the young. Nest success and duckling or gosling survival strongly influence recruitment, which is the number of young that survive to breed the following spring.
Waterfowl recruitment is usually very good in wet years on the prairies like the 1970s and mid-1990s, and often decreases during drought years like the 1980s and early 2000s. When weather and habitat conditions are excellent, hens may renest several times if their earlier nesting attempts are unsuccessful because ideal wetland conditions assure excellent food supplies for ducklings. In dry years, wetlands are much less productive. As a result, hens nest less aggressively and produce fewer young. During these years, even ducklings that successfully hatch have lower survival because of reduced food supplies and more frequent movements between wetlands in search of food.
Likewise, duckling survival is highly variable and may be as low as 10 percent or higher than 70 percent. It seems that virtually any animal that is slightly larger than a duckling will eat it. In my research in the rivers and swamps of Mississippi and Alabama, I attached radio transmitters to nesting wood duck hens and their ducklings. I found that red-shouldered hawks, owls, fish, cottonmouths, snapping turtles, great blue herons and other predators ate about 300 of 435 radio-marked ducklings that I studied.
Besides predators, young waterfowl are sometimes exposed to harsh environmental conditions such as cold, rain and wind. Heavy rain, especially when accompanied by cold temperatures, can temporarily decrease the amount of insects available to ducklings. Inclement weather also compels the hen to increase brooding time to try to prevent the young birds from dying from hypothermia. For ducklings and goslings, more time spent brooding may mean less time available for feeding. Researchers in North Dakota have found that total loss of mallard broods may be five times more likely on days when it is raining than on days when it is dry.
Clearly, high-quality grasslands and wetlands are critical for nesting waterfowl and their broods. We cannot control droughts, but policies and management practices that promote large tracts of grassland and that prevent wetland drainage are vital for nesting success. Conserving these essential waterfowl breeding habitats is also the best way to ensure that the downy little birds hatched in spring will survive to wing their way south each autumn.
Dr. Brian Davis is a DU regional biologist based in Little Rock, Ark.