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Population Dynamics of Breeding Waterfowl

II. Number of Potential Breeding Birds

C. Synopsis

The number of birds available to breed depends on past reproduction as well as survival, homing, and pioneering. Survival rates tend to be highest for swans, intermediate for geese, and lowest for dabbling and diving ducks. Older birds typically survive at a higher rate than first-year birds. Much mortality of breeding birds occurs during nesting and brood-rearing, so males and females have similar survival rates if they share those duties, but females survive at a lower rate if they are primarily responsible for incubating and brood-rearing. Survival is sometimes greater among birds with greater nutrient reserves. Survival rates vary geographically and temporally, and there is some evidence of density-dependence.

Homing and pioneering tendencies vary markedly among species, often corresponding to the stability of favored habitats and the timing of pair formation. Homing tends to be greater among older birds and, in some species, among birds that nested successfully the previous season. In ducks, females are usually much more philopatric than males, whereas in geese and presumably swans, the longer pair bonds are associated with more similar homing rates for the sexes. Homing is less frequent to areas with unsuitable wetland conditions; conversely, many species of ducks pioneer into areas with favorable wetland conditions.

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