Those that have been watching the progress of the shopping trolley Coots over time will know that as the nesting season progresses, the nest slowly gets taller until they reach such a point that they are in a position to perhaps attain success. When I went to see them yesterday, I watched their futile nest saving attempts when the water was almost at the high tide mark, and could see it in action.
A nest doing wet, with a nice polystyrene cup
While they are at high water, the bird that is sitting on the nest (presumably the female) stays in situ whilst the other bird (presumably the male) frantically collects more material from the surrounding water course and takes it to the bird on the nest. The bird on the nest takes these offerings and adds it to the structure of the nest. The behaviour that the incumbent bird carries out can be seen in Swans, Geese and Ducks in a normal nesting situation (and perhaps any bird) - if they can reach something that is suitable for nest material without leaving the nest, it goes in. As the water is rising, and to an extent the bird begins to float, it will use the fresh material to fill the gap that is underneath it and slowly increase the overall height of the nest. Simple really.
Obviously, while this is going on they are trying to protect the eggs, but cannot. Remember that the nest got so big last year that before the eggs could hatch out the whole thing detached itself from the moorings and floated off but if they continue like this and get lucky it might turn out ok.
Elsewher on the Wandle yesterday I noticed another pair of Coots running around with nesting material, in a tidal area. Great.
Coots doing nesting handover behaviour