Barn Owls moult their feathers gradually throughout their lives. However, there is some variation in the timing. For example, while the female is incubating eggs and tending young chicks, she is permanently at the nest for almost 2 months, during which time she is fed by the male. During this 'down time' she moults some of her feathers, when there is less pressure on her to hunt efficiently. At the same time, males suspend their moult while provisioning the female and young, and rather than have energy spent on replacing feathers, it is used to provide food for the female and young over the entire breeding period. Once the breeding season is over, both male and female resume the gradual moult of their feathers.
The video below was filmed last night at one of our Duhallow nest sites in a derelict cottage. We see very fresh pellets (indicating the adults are still present) and a series of newly moulted feathers, including a large flight feather (a primary). There were many fewer feathers on our last visit here about two weeks ago and during last nights' visit the cottage was utterly silent – no young chicks calling for food and no activity noted around the nest – the conclusion being that it is most likely that the adults have failed to breed, and as a result, have resumed their moult. Perhaps another effect of the extremely wet summer.
Video of fresh pellets and newly moulted feathers below a Duhallow nest site. Signs that breeding has not taken place (Filmed under licence from NPWS. M.O'Clery).