This video from the USA says about itself:
27 January 2016
A female American Robin reinforces her nest with mud. Females build the nest from the inside out, pressing dead grass and twigs into a cup shape using the wrist of one wing. Other materials include paper, feathers, rootlets, or moss in addition to grass and twigs. Once the cup is formed, she reinforces the nest using soft mud gathered from worm castings to make a heavy, sturdy nest. She then lines the nest with fine dry grass. The finished nest is 6-8 inches across and 3-6 inches high.
Video recorded by Marie Read/Macaulay Library.
From the Cornell Lab of Ornithology in the USA, 8 May 2017:
This American Robin is sitting on four eggs—and the first one hatched today.
Discover Robins From A New Perspective
The red breast and cheery song of the American Robin are common sights and sounds across much of North America. Here at the Cornell Lab, robins often nest on our building and throughout Sapsucker Woods. This year, we’re lucky enough to have a nest that’s easy to access, and we’re excited to share the opportunity to watch from a front row seat. Watch cam.
The female has been incubating the nest for about the last 12 days, and once the eggs hatch it will be a mad dash for the parents as they forage for themselves and the ravenous appetites of the growing young. But be sure not to blink—it will only take about 12-14 days for the nestlings to fledge! Learn more about robins in our AllAboutBirds.org species guide.