Cormorants are highly successful aquatic birds, recognized globally for their exceptional diving and fishing abilities. They are often seen standing with wings outstretched to dry their non-waterproof plumage. These large birds typically congregate in massive, noisy colonies for the breeding season. Unlike avian species that form permanent lifetime partnerships, the cormorant’s approach to pairing is flexible and tied directly to reproductive demands. Their pair bonds are functional arrangements designed to maximize offspring survival during a single reproductive cycle.
Cormorant Mating Fidelity
Cormorants practice serial monogamy, committing to one partner for the duration of a single breeding season. This commitment is functional, as raising young requires the intense effort of two dedicated parents. Once the chicks fledge and become independent, the pair bond typically dissolves, and the birds disperse.
The partners generally separate during the non-breeding season. When they return to the colony the following year, they usually seek out a new mate. While a pair may reunite for a second or third season, this is not the standard pattern of their reproductive life cycle. The default behavior is to select a new partner, contrasting with birds that maintain a lifelong attachment.
The Annual Pairing Process
Pair bond formation begins with the male arriving first at the colony to select and defend a suitable nesting site. Site fidelity is common, with males often returning to the same general area year after year to establish their territory. Once secured, the male engages in conspicuous courtship rituals to advertise for a female.
These displays are often elaborate, involving a “wing-waving” stance that shows off the bright colors of his face, neck, and gular pouch. Courtship dances may occur in the water, or the male may present the female with small pieces of nesting material. After the female accepts the invitation, the pair solidifies their bond through mutual preening, neck intertwining, and sometimes clasping bills. The pair bond is thus established anew each year through this suite of behaviors.
Nesting and Shared Parental Duties
Once the partnership is fixed, the pair begins building or repairing a nest, typically a bulky structure made of sticks, twigs, and seaweed. The division of labor is clear: the male gathers the majority of the materials, sometimes including flotsam like rope or balloons, and delivers them to the female. The female then arranges the debris into a secure, bowl-shaped nest.
The female generally lays a clutch of three to four pale blue or chalky white eggs. Both parents take turns incubating the eggs for about four weeks. The eggs are sometimes held on the parents’ feet, a behavior that aids in temperature regulation. After the altricial young hatch—naked and helpless—the parental commitment intensifies.
Both adults are tasked with feeding the chicks, requiring them to forage constantly and return to the nest to regurgitate fish. In colonies with nests exposed to the sun, parents also shade the young and deliver water by pouring it from their bill into the chicks’ mouths. This intense, shared commitment maintains the pair bond until the chicks fledge and achieve independence, which can take up to nine weeks.