Cost of reproduction in breeding female mallards : predation risk during incubation drives annual mortality / Todd W. Arnold, Erin A. Roche, James H. Devries, and David W. Howerter.

Includes bibliographical references.

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these
costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of
reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured
seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through
brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests
in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached
seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards
were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding
stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent
with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived
better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards,
the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in
terrestrial habitats.