The whooper swan is still in and around our backyard pond. It has been here since July 26.
I think it is probably molting and will stay as long as it takes to grow new flight feathers.
Some birds, such as ducks, swans, grebes, pelicans, and auks, are “synchronous molters — they change their feathers all at once in a period as short as two weeks, but sometimes stretching over a month. During this period, they cannot fly, and males, in particular, often complete the process on secluded lakes in order to minimize their vulnerability to predators.
Why should synchronous molters have evolved this seemingly risky process instead of undergoing a gradual molt like most birds? These birds tend to be heavy relative to their wing surfaces — they have high “wing loadings.” The loss of only a few flight feathers would seriously compromise their flying ability, and so evolution has favored being grounded for a “quick overhaul” rather than a longer period of difficult flying.