黑嘴天鹅种

The trumpeter swan (Cygnus buccinator), or simply the trumpeter, is a species of swan found in North America. The heaviest living bird native to North America, it is also the largest extant species of waterfowl, with a wingspan of 185 to 304.8 cm (6 ft 2 in to 10 ft 2 in). It is the American counterpart and a close relative of the whooper swan (Cygnus cygnus) of Eurasia and has even been considered the same species by some authorities. By 1933, fewer than 70 wild individuals were known to exist; extinction seemed imminent until aerial surveys discovered a Pacific population of several thousand trumpeter swans around Alaska's Copper River. Careful reintroductions by wildlife agencies and the Trumpeter Swan Society gradually restored the North American wild population to over 46,000 birds by 2010.

Taxonomy

The trumpeter swan was formally described in 1831 by the Scottish naturalist John Richardson in the fourth volume of American Ornithology; or, The Natural History of Birds Inhabiting the United States by Alexander Wilson and Charles Bonaparte. Richardson coined the current binomial name Cygnus buccinator. A description by Richardson was also published in Fauna Boreali-Americana, or, The Zoology of the Northern Parts of British America by William Swainson and Richardson.

Description

The trumpeter swan is the largest extant species of waterfowl, and both the heaviest and longest native bird of North America. Adults usually measure 138–165 cm (4 ft 6 in – 5 ft 5 in) long, though large males can exceed 180 cm (5 ft 11 in) in total length. The weight of adult birds is typically 7–13.6 kg (15–30 lb).

Range and habitat

Cooperative continental surveys of trumpeter swans have been performed regularly, beginning in 1968, repeated in 1975, and then conducted at 5-year intervals. The most recent survey of trumpeter swans occurred in 2015. The survey assesses trumpeter swan abundance and productivity throughout the entire breeding ranges of the three recognized North American populations: the Pacific Coast (PCP), Rocky Mountain (RMP), and Interior (IP) populations (see Figure).

Diet

These birds feed while swimming, sometimes up-ending or dabbling in reaching submerged food. The diet is almost entirely aquatic plants and occasionally insects. They will eat both the leaves and stems of submerged and emergent vegetation. They will also dig into muddy substrates underwater to extract roots and tubers. In winter, they may also eat grasses and grains in fields. They will often feed at night as well as by day.

Predators and mortality

Predators of trumpeter swan eggs include common ravens (Corvus corax), common raccoons (Procyon lotor), wolverines (Gulo gulo), American black bears (Ursus americanus), grizzly bears (Ursus arctos horribilis), coyotes (Canis latrans), gray wolves (Canis lupus), pumas (Puma concolor), and North American river otters (Lontra canadensis). Nest location can provide partial protection from most mammalian nest predators, especially if placed on islands or floating vegetation in deep waters.

Breeding behaviour

Courtship and mate choice behaviours

Like other swans, trumpeter swans often mate for life, and both parents participate in raising their young, but primarily the female incubates the eggs. Most pair bonds are formed when swans are 5 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 mates in differing breeding seasons. Occasionally, if his mate dies, a male trumpeter swan may not pair again for the rest of his life.

Conservation status

Near extinction and rediscovery in Alaska

In the 19th and early 20th centuries, the trumpeter swan was hunted heavily, for game or meat, for the soft swanskins used in powder puffs, and for their quills and feathers. This species is also unusually sensitive to lead poisoning from ingesting discarded lead shot from fishing weights while young. The Hudson's Bay Company captured thousands of swans annually with a total of 17,671 swans killed between 1853 and 1877.