The yolk is rich in fat and proteins, and provides food required by the developing embryo. The egg is enclosed in a tough double membrane that is covered by a hard, breathable shell made of calcium carbonate. That shell is designed to withstand the parents' weight during incubation. A single robin nestling can eat 14 feet of worms in a day. During the nesting period, the parents are likely to bring three pounds of invertebrates to the nest to feed those hungry little birdbrains.
Robins are amazingly prolific, averaging two to three clutches each year.
Robins hatch without feathers but soon are covered with gray down. As they grow their first set of feathers both sexes will have black flecks on their breasts. Once the fledglings leave the nest, the male will continue to feed the young birds while the female starts another clutch. More than 60 percent of robin eggs or hatchlings will perish by the time they leave the nest. Grackles, blue jays, crows, squirrels, cats, and dogs are all high on the list of predators.