As unusual as the gull that nests in trees, this one builds a floating nest.
Here in North America, Franklin’s gulls are prairie birds. They spend the winter on the Pacific coast of South America, then migrate in Spring to the prairie marshes of Canada, Montana and the Dakotas where they look for shallow lakes to nest colonially. Every year they assess the water depth and vegetation density when they arrive. Droughts or floods force them to choose different marshes than they used the year before.
Like other marsh birds, Franklin’s gulls have learned that land-based nests are in danger of predation so they build floating nests out of bulrushes, cattails or phragmites. To keep the nests from drifting they anchor them to underwater reeds.
Unfortunately the submerged material decays and the nest sinks so the pair and their oldest chicks add more nest material every day to raise the surface.
If you have to work this hard to keep your nest from disappearing you eventually find time-saving shortcuts. Picking new bulrushes takes a long time, seven times longer than stealing your neighbor’s nesting material (someone actually timed this). Naturally a lot of stealing occurs.
Build and sink, build and sink, the floating nest requires daily upkeep and annoys the neighbors.