Influence of Female Age and Body Mass on Brood and Duckling Survival, Number of Surviving Ducklings, and Brood Movements in Redheads

I documented brood and duckling survival, the number of surviving ducklings, and brood movements of Redheads, and examined the association between these variables and female age and body mass. Redhead brood success was 55% and duckling daily survival rates averaged 0.868. Female body mass, but not age, was related to brood and duckling survival and the number of surviving ducklings. Successful females were heavier and produced more ducklings. All brood-movement measures differed between successful and unsuccessful females, however, the distance of the first move between wetlands accounted for the most variability in brood success. Increased body mass, but not age, was associated with longer first brood movements.

Factors affecting brood abandonment in gadwalls (Anas strepera)

Brood desertion by radio-equipped female gadwalls (Anas strepera) was examined to test three hypotheses regarding proximate factors responsible for post hatch brood abandonment in waterfowl. Gadwall broods with the greatest duckling mortality, independent of brood size, were more likely to be abandoned, providing support for the "brood-success" hypothesis. Our results do not support the "brood-size" hypothesis, as the size of broods immediately prior to female abandonment was no smaller than the size of broods not abandoned. Although brood fate was not related to female body condition, the "salvage-strategy" hypothesis could not be rejected, because experience was a confounding factor and could not be sampled adequately; younger, possibly less-experienced females were more likely to abandon their broods than older females. Further studies, preferably involving experimental manipulations, are needed to adequately address the full array of hypotheses.

Factors affecting abandonment and adoption of young in common eiders and other waterfowl: a comment

Factors affecting abandonment and adoption of young have been studied extensively in waterfowl. Several hypotheses have been advanced to account for these behaviours, and Bustnes and Erikstad (J.O. Bustnes and K.E. Erikstad. 1991. Can. J. Zool. 69: 1538–1545) recently evaluated these in common eiders (Somateria mollissima). They found, among other things, that young of "abandoners" had a lower survival rate than young of "tenders," but were not able to accurately time the mortality of ducklings. I propose a hypothesis based on brood success and parental investment theory to explain why some parents abandon their young exceptionally early and why some parents tend their own as well as foreign young. According to the hypothesis, parents provide relatively less care for offspring that are surviving less than average during the parental care period. The low survival of the young of abandoners while they are still with their own mother may have influenced the final decision of common eider females to abandon their broods early.