Trumpeter Swan - Breeding

Breeding

These birds often mate for life, and both parents will participate in raising the cygnets, but only the female will incubate the eggs. Most pair bonds are formed when swans are 4 to 7 years old, although some pairs do not form until they are nearly 20 years old. "Divorces" have been known between birds, in which case the mates will be serially monogamous, with different mates in differing breeding seasons. Occasionally, if his mates dies, a male Trumpeter Swan may not pair again for the rest of his life. Most egg laying occurs between late April and May. The female lays 3–12 eggs, with 4 to 6 being average, in a mound of plant material on a small island, a beaver or muskrat lodge, or a floating platform on a clump of emergent vegetation. The same location may be used for several years and both members of the pair help build the nest. The nest consists of a large, open bowl of grasses, sedges and various aquatic vegetation and have ranged in diameter from 1.2 to 3.6 m (3.9 to 12 ft), the latter after repeated uses. The eggs average 73 millimetres (2.9 in) wide, 113.5 millimetres (4.5 in) long, and weigh about 320 grams (11.3 oz). The incubation period is 32 to 37 days, mainly by the female, although occasionally by the male as well. The young are able to swim within two days and usually are capable of feeding themselves after at most two weeks. The fledging stage is reached at roughly 3 to 4 months. While nesting, Trumpeter Swans are territorial and harass other animals, including conspecifics, who enter the area.

Adults go through a summer moult when they temporarily lose their flight feathers. The females become flightless shortly after the young hatch; the males go through this process about a month later when the females have completed their moult.