The Franklin's Gull is unique among gulls in having two complete molts each year rather than one.
The floating nest of the Franklin's Gull gradually sinks as the material below the water surface decays, and it requires continual maintenance. Both parents add new nest material daily until one or two weeks before departing the colony. Older chicks also add nest material from the immediate vicinity of the nest.
In breeding plumage, and sometimes in nonbreeding plumage as well, the Franklin's Gull often shows a rosy pink cast (rarely salmon) on its chest and abdomen. This color is most apparent on the shafts and bases of its feathers. The color fades as the breeding season progresses as the pigment is broken down by sunlight.
The oldest recorded Franklin's Gull was at least 9 years, 5 months old when it was shot in Montana in 1972. It had been banded in the same state in 1963.