Male Robins are basically the same pattern as females, but with brighter colors. Fledglings have light spots all over their bodies, but otherwise resemble adults. Robins build an open cup nest on a horizontal limb or in the main crotch of a tree. Usually the basic nest structure is grass and the whole nest is lined with mud which serves to bind the grass into a firm structure. After the mud dries, the nest has remarkable strength.
Most nests receive an inner lining of soft material such as moss.
Incubation is mostly by the female, but both sexes feed the young, and, after fledging, the male may continue to feed the chicks for a short period while the female begins a second brood. In mid summer, in many areas, abandoned Robin nests are much preferred for the later nesting attempts of Mourning Doves. Robins gather in remarkably large flocks in fall migration and winter, usually centered on favorable food supplies. It is not uncommon to find 100 or more in a single berry-bearing tree such as a holly, cotoneaster, etc.