Males are more showy to attract the female. Some species are not greatly different from female, but still can be identified. ALL waterfowl molt after the nesting period and are flightless for a short period. During this time they are vulnerable to predation and being caught by biologists for banding. Males and females look similar during this period.
Period varies with species.
Blue winged teal are in eclipse July through December. This eclipse plumage is replaced by the breeding plumage again, BUT wing feathers are not lost and there is no flightless period in this molt. In Sea ducks, the breeding plumage does not appear until second fall. Mergansers that breed on New England lakes may winter on New England coast. Some species of sea ducks shift to open water in winter.