Hunlock Creek PA
2011

https://www.birdsandblooms.com/birding/attracting-birds/bird-nesting/robins-nests-robins-eggs/

In a robin couple, a male brings his female partner nesting material as she constructs the robins’ nest. The female builds the cup-like nest with mud as its foundation and lines it with grasses, twigs and other plant material before laying bright blue robin eggs.

Mud is an essential part of robin nest architecture. The foundation is constructed of mud that holds the nest together like cement. The mud is typically gathered from a ready source, such as the edge of a puddle or earthworm castings.