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The survival rate of hatched young, the probability that an individual hatchling will survive until fledging, involves both the loss of entire broods and the loss of individuals within broods. Reported brood survival rates of waterfowl are typically low, mostly ranging from 0.40 to 0.60. Losses are particularly intense during the early stages of brood-rearing.

Identified causes of brood mortality, in order of apparent importance, include predation, exposure to adverse weather, starvation, attacks by other ducks, diseases, and parasites. Mendenhall and Milne (1985) evaluated the effects of mortality agents of Eider young and concluded that predation was the most important but was influenced by weather conditions and possibly parasitic infections. A variety of predators have been implicated in brood losses, including fish (bowfin, eel, northern pike, and large-mouth bass), amphibians (bullfrog), reptiles (marine and snapping turtles), mammals (fox, raccoon, mink, feral cats, and humans), and birds (cormorants, jaegers, skuas, gulls, herons, cranes, coots, hawks, owls, and crows). Larids are implicated especially often. Dwernychuk and Boag (1972) found greater loss of ducklings of several species on islands with greater numbers of nesting gulls. Vermeer (1968) found virtually no ducks fledging on islands occupied by California and Ring-billed Gulls, partly because the island shores lacked any protective vegetative cover. Lynch and Toepfer (1975) indicated that the only brood (of 14) not destroyed by gulls left the nesting island after the gulls had completed nesting and departed.

Young waterfowl are sensitive to weather extremes, mostly involving cold, rainy, or windy conditions (Hildén 1964, Reynolds 1965, Erskine 1971, Bengtson 1972b, Williams 1979, Gray 1980, Makepeace and Patterson 1980, Thomas 1980, Moulton and Weller 1984, Mendenhall and Milne 1985). Hail (Smith and Webster 1955) and above-normal temperatures in late May and June (Hammond and Johnson 1984) have also been implicated. Weather-associated losses can result from exposure, reduced food availability (Pehrsson 1984), or inability to exploit available foods. Prince (1965) indicated that exposure of duckings to severe weather was increased by brood separation caused by disturbance. Talent, Jarvis, and Krapu (1983) reported the loss of two Mallard broods, apparently to exposure, when hens, evidently in poor physical condition, fed away from the ducklings in cold, rainy weather. Patterson (1982) alluded to indirect effects of adverse weather, such as increased energy losses heightening chances of later mortality. Stormy weather can force ducklings into calm bays where gull predation is severe (Bergman 1982). Mendenhall and Milne (1985) indicated that predation mortality on Eider ducklings was 2.5 times more severe in windy and rainy weather than under calm and dry conditions; the difference was attributed to young feeding farther from the adult female.

Late-hatched young in northern breeding areas are susceptible to severe weather before they complete their development (Dement'ev et al. 1967, McLaren and McLaren 1984). For the Black Swan, which can breed at any time during the year, Braithwaite (1982) detected greater survival of Black Swan cygnets for hatches in summer and autumn than in the colder weather of winter and spring.

Starvation is probably a major cause of mortality among young waterfowl, but the phenomenon is difficult to detect and identify with certainty. Most reports have been only suggestive (e.g., Reynolds 1965, Titman 1969, Ogilvie and St. Joseph 1976, Ankney 1980, Duncan 1986).

Attacks by adult ducks on ducklings have been reported (Pienkowski and Evans 1982), usually in crowded situations where food might be limiting. Gauthier (1987b) observed adult female Buffleheads killing young Buffleheads and Goldeneyes. Hansson (1966) reported Mallard ducklings killed by adult males in a crowded situation. Also, Savard (1987) noted that fights between female Barrow Goldeneyes led to the loss of young of the defeated female.

It is difficult to identify losses of ducklings to diseases or parasites, so reports tend to be general and anecdotal, rather than quantitative. Moreover, a diseased duckling may be more disposed to predation or weather mortality than a healthy one. There are scattered reports of disease affecting young waterfowl in North America. Outside of North America, Hildén (1964) thought disease to be important for ducklings in a population of Eiders. Dement'ev et al. (1967) claimed that parasitic diseases kill a number of young Red-breasted Mergansers. Mendenhall and Milne (1985; also see references contained therein) found a greater parasite load in Eider ducklings found dead than in those they collected, and suggested that parasites could increase vulnerability to weather stress or predation. They also considered renal coccidiosis an important component of nonpredation mortality for ducklings 5 to 18 days old.

1. Age and Breeding Experience

2. Density, Crèching Behavior, and Brood Size

Under some circumstances, high densities of waterfowl young may enhance survival. Findlay and Cooke (1982) suggested that high densities of young Snow Geese, associated with hatching synchrony, enhanced survival through a dilution effect, in which the probability of an individual bird being preyed upon was reduced, and by sharing information about food sources. Munro and Bédard (1977) found a significant increase in duckling survival rate with the number of Eider ducklings in a crèche when attacked by individual gulls, suggesting a benefit by being part of a larger group. Larger crèches were more likely to be attacked by groups of gulls, however. Kehoe (1989) reported greater survival of White-winged Scoter ducklings in large groups (more than 7) than in smaller ones. Williams (1974) noticed lower survival but more rapid growth of Northern Shelduck young when crèched than when in family broods. Eadie and Lumsden (1985) suggested that nest parasitism, with resulting larger broods, could enhance the survival of the host's young by buffering predation.

Brood size does not seem to affect survival of young (Wang 1982 for Canada Geese, Rohwer 1985 for Blue-winged Teal, Dow and Fredga 1984 for Goldeneye). Clawson, Hartman, and Fredrickson (1979) noticed no difference in brood survival of Wood Duck ducklings from normal versus dump nests, which usually contain more young. LeBlanc (1987a), however, found in one year lower survival rates of Canada Geese goslings in larger broods. Conversely, Prop, van Eerden, and Drent (1984) indicated that larger broods of Barnacle Geese survived at a higher rate, possibly because their families had a higher dominance status and could secure better feeding sites.

3. Wetland Habitat

Foods available to young waterfowl can affect survival. Among Black Swans, scarcity of preferred foods may be the major factor causing loss of cygnets (Braithwaite 1982). Hill and Ellis (1984) claimed greater chances of Tufted Duck duckling survival if the hatch coincided with the peak of chironomid abundance. Haramis and Chu (1987) for captive Black Ducks and McAuley and Longcore (1988) for Ring-necked Ducks found lower survival of ducklings on wetlands with low pH, which they attributed to reduced diversity and abundance of invertebrate foods.

There are suggestions that long overland moves by broods may reduce their chances of survival (Ball et al. 1975 for Wood Duck and Mallard, Eriksson 1979 for Goldeneye). Haramis and Thompson (1984) attributed the high estimated brood survival they observed among Wood Ducks to flooded habitat and the resultant absence of overland travel. Hill, Wright, and Street (1987) reported greater brood mortality rates of Mallards with increased home range size, possibly due to greater movement in response to food shortages. Hori (1964) noted greater loss of Northern Shelduck young for nests farther from brood-rearing waters; ducklings were lost to traffic, dogs, and children, or deserted along the way. Talent, Jarvis, and Krapu (1983), on the other hand, noticed no effect of distance traveled on survival of young Mallards. The effect may not involve physical condition: Duncan (1987c) found that a 3-km walk did not significantly reduce body lipids of day-old Pintails.

4. Timing of Hatch

5. Attentiveness of Parent

6. Indirect Effects

7. Synopsis