Cormorants nest in colonies. Both the males and females build the nests which take about 4 days to build. Old nests may be used for 4 years. Nests are built in trees out of sticks and weed stems and are lined with leafy twigs and grass. Nests built on rocks are often made of seaweeds and trash gathered at the water's edge or in diving.
Cormorants add objects like feathers and twigs of evergreen.
Usually 3-4 chalky, pale blue eggs are laid from April through July. They have a single brood but may re-lay if nest or eggs are destroyed. Incubation is 24 days, with both males and females taking turn. Both parents feed chicks. The first flight of the chicks is usually to water at about 35 days after hatching, but chicks can dive even earlier.