—John M. Coluccy, Ph.D., and Kurt A. Anderson
A variety of factors influence how many young ducks fly south each fall
Nest success has long been touted as the most important factor in maintaining healthy duck populations. But recent research indicates that duckling survival also plays a crucial role in population dynamics. The premise is simple: while eggs must hatch to produce young, young must also survive to be recruited into the breeding population. Greater duckling survival often means larger fall duck populations.
Despite its importance in population dynamics, duckling survival is one of the most poorly understood components of the waterfowl life cycle. It takes 50-70 days for ducklings to attain flight status, and survival during this period is highly variable, ranging from less than 10 percent to as high as 70 percent. The most common causes of duckling mortality include predation, adverse weather conditions, starvation, disease, and parasites. Ducklings are excellent fare for nearly every type of predator, including fish (largemouth bass and northern pike), amphibians (bullfrogs), reptiles (snakes and snapping turtles), and mammals (foxes, raccoons, mink, and feral cats). Likewise, other birds such as hawks, owls, gulls, herons, and crows will make a meal of ducklings.
Ducklings are sensitive to weather extremes. While their fuzzy down feathers are an excellent source of natural insulation in dry weather, they are of little value when wet. Ducklings also lack the additional thermal support of adult contour feathers. Cold, rainy, and windy conditions can lead to death from exposure (hypothermia) and may either reduce food availability or prevent ducklings from exploiting food resources. Additionally, ducklings can be killed by hail or above-average temperatures. In the summer of 1953, an estimated 148,000 adult and young waterfowl perished because of severe hail storms in Alberta.
Like a Duck Out of Water
When departing the nest, upland-nesting hens often travel overland with their young to reach brood-rearing wetlands. Family units also travel overland when hens lead their broods in search of undisturbed wetlands with ample cover and food resources. Surprisingly, duck families often don't travel to the nearest wetland and may waddle considerable distances (a mile or more) along paths, roadways, trails, or watercourses and through dense vegetation or wide-open areas. Ducklings are especially susceptible to predation during overland travel and may also become exhausted or disoriented, resulting in separation from the brood.
Research has identified several additional factors influencing duckling survival, including age of ducklings and hens, brood size and movement, hatch date, and habitat conditions. During the first week following hatch, ducklings are extremely vulnerable to hypothermia and predation. A recent study in Ontario found that daily survival of mallard ducklings was nearly nine times greater for older ducklings (those more than seven days old) than for younger ducklings. Similarly, older hens benefit from past experience raising broods, social dominance, better body condition, and the ability to devote greater resources to reproduction. Older hens should therefore have a clear advantage when it comes to raising young. Nevertheless, a positive relationship between hen age and duckling survival has been demonstrated only in gadwall and a few other waterfowl species.
The date of hatch may influence duckling survival as well. An increase in survival of earlier-hatched ducklings has been observed in several species. Mallards and northern pintails, which are among the first ducks to nest in spring, are known to benefit from an advanced hatch date, as do many other species. This pattern is thought to be related to a decreased risk of predation, greater wetland quality and food availability, and increased maternal care earlier in the breeding season. Because early nesting females typically enjoy higher nest success and duckling survival, they may make a disproportionately large contribution to duck recruitment. Interestingly, lesser scaup may benefit from a delayed hatch, which could explain their tendency to initiate nesting after most ducklings of other species have already hatched.
Traits such as size, body condition, and gender may also be important determinants of duckling survival. Larger offspring have larger yolk reserves and may benefit from greater mobility, higher feeding efficiency, and the ability to withstand colder temperatures. Therefore, larger ducklings, which are presumably in better condition, enjoy higher survival than smaller ducklings. Few studies have evaluated differences in survival between male and female ducklings, and existing results are conflicting.
Perhaps the most important factor influencing duckling survival is habitat. Research has shown that duckling survival is greater in landscapes that contain abundant seasonal wetlands with a mix of emergent vegetation and open water. A greater density of this wetland type on the landscape provides hens and broods with options, as they are able to move in response to disturbance, foraging conditions, and pressure from predation. When seasonal wetlands are lost because of wetland drainage or drought, options for hens and ducklings are limited. Broods that travel overland in search of suitable habitat must cover greater distances between wetlands, increasing their exposure to predators. Moreover, when broods reach their destination, they are more likely to encounter mink, which also may be concentrated in remaining wetland habitats.
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