A robin with a beakful of dried grasses — or one with mud smeared on its breast feathers — is a sure sign that nesting-building has begun. Both the male and female gather nest materials, but the female is usually the only one that does the building. It's hard work to construct a nest that's only about 3-8 inches in diameter.
Important to Remember: Avoid using chemical pesticides on lawns, watch a nest from a distance, keep cats indoors, and do not disturb. The nest is a nursery for eggs and babies.