Predation is the primary source of mortality of dabbling duck nests, so a key aspect of parental investment is defending the nest from predators. The hen's presence on the nest is widely considered to be a good measure of nest defense; an incubating female camouflages the nest and may physically deter nest predators. Parental-investment theory suggests that investment should increase with the reproductive benefits expected from the current clutch of eggs. We used nest-temperature loggers to study how the rhythms of waterfowl incubation changed after the nest was partially destroyed by a predator. Contrary to the expected-benefits hypothesis, we found that hens significantly increased their investment after partial clutch loss: they took fewer recesses from incubation per day and extended their incubation by more than 200 min after a partial depredation. We suggest that when predators pose little risk to the incubating adult, those hens unable or unwilling to abandon a nest after partial clutch loss will increase parental investment to obtain at least some reproductive benefits.