The Adaptive Significance of Clutch Size in Prairie Ducks

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Abstract
Experimental manipulations of clutch size showed that neither incubation nor brood rearing constrains clutch size of blue-winged teal (Anas discors). Manipulated nests with small (.hivin.x = 4.9), normal (.hivin.x = 9.9), or large (.hivin.x = 16.0) clutch sizes did not differ significantly in nest success (72.5%), hatchability (94.8%), or incubation periods (24.5 days). Survival of ducklings hatching from experimental nests was not related to the initial size of the brood, nor was ducking weight (at 35 days post-hatch) related to the initial brood size. Differences in duckling survival rates between years were associated with pronounced differences in habitat conditions. The variance of survival rates did not differ between the 3 brood size classes in either the wet or dry years. The variance in success among normal and large broods was significantly greater than that predicted from a binomial distribution. The size of the clutch being incubated did not affect the weight of females in late incubation, nor did brood size affect the weight of females accompanying nearly flying young. The results from this study are consistent with most of the limited data available for other waterfowl.

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