| abstract | - The trumpeter swan is the largest extant species of waterfowl. Adults usually measure 138–165 cm (4 ft 6 in–5 ft 5 in) long, though large males can exceed 180 cm (71 in) in total length. The weight of adult birds is typically 7–13.6 kg (15–30 lb). Possibly due to seasonal variation based on food access and variability due to age, average weights in males have been reported to range from 10.9 to 12.7 kg (24 to 28 lb) and from 9.4 to 10.3 kg (21 to 23 lb) in females. It is one of the heaviest living birds or animals capable of flight. Alongside the mute swan (Cygnus olor), Dalmatian pelican (Pelecanus crispus) and Andean condor (Vultur gryphus) and the kori bustard (Ardeotis kori), it is one of the handful to scale in excess of 10 kg (22 lb) between the sexes and one survey of wintering trumpeters found it averaged second only to the condor in mean mass. The trumpeter swan's wingspan ranges from 185 to 250 cm (6 ft 1 in to 8 ft 2 in), with the wing chord measuring 60–68 cm (24–27 in). The largest known male trumpeter attained a length of 183 cm (72 in), a wingspan of 3.1 m (10 ft 2 in) and a weight of 17.2 kg (38 lb). It is the second heaviest wild waterfowl ever found, as one mute swan was found to weigh a massive 23 kg (51 lb), but it has been stated that was unclear whether this swan was still capable of flight due to its bulk. The adult trumpeter swan is all white in plumage. Like mute swans cygnets, the cygnets of the trumpeter swan have light grey plumage and pinkish legs, and gain their white plumage after about a year. As with a whooper swan, this species has upright posture and generally swims with a straight neck. The trumpeter swan has a large, wedge-shaped black bill that can, in some cases, be minimally lined with salmon-pink coloration around the mouth. The bill, measuring 10.5–12 cm (4.1–4.7in), is up to twice the length of a Canada goose's (Branta canadensis) bill and is the largest of any waterfowl. The legs are gray-pink in color, though in some birds can appear yellowish gray to even black. The tarsus measures 10.5–12 cm (4.1–4.7 in). The mute swan, introduced to North America, is scarcely smaller. However, it can easily be distinguished by its orange bill and different physical structure (particularly the neck, which is always curved down as opposed to straight in the trumpeter). The mute swan is often found year-around in developed areas near human habitation in North America, whereas trumpeters are usually only found in pristine wetlands with minimal human disturbance, especially while breeding. The tundra swan (C. columbianus) more closely resembles the trumpeter, but is significantly smaller. The neck of a male trumpeter may be twice as long as the neck of a tundra swan. The tundra swan can be further distinguished by its yellow lores. However, some trumpeter swans have yellow lores; many of these individuals appear to be leucistic and have paler legs than typical trumpeters. Distinguishing tundra and trumpeter swans from a distance (when size is harder to gauge) can be challenging without direct comparison but it is possible thanks to the trumpeter's obviously longer neck (the great length of which is apparent even when the swan is not standing or swimming upright) and larger, wedge-shaped bill as compared to the tundra swan. Trumpeter swans have similar calls to whooper swans and Bewick's swans. They are loud and somewhat musical creatures, with their cry sounding similar to a trumpet, which gave the bird its name. Their breeding habitat is large shallow ponds, undisturbed lakes, pristine wetlands and wide slow rivers, and marshes in northwestern and central North America, with the largest numbers of breeding pairs found in Alaska. They prefer nesting sites with enough space for them to have enough surface water for them to take off, as well as accessible food, shallow, unpolluted water, and little or no human disturbance. Natural populations of these swans migrate to and from the Pacific coast and portions of the United States, flying in V-shaped flocks. Released populations are mostly non-migratory. In the winter, they migrate to the southern tier of Canada, the eastern part of the northwest states in the United States, especially to the Red Rock Lakes area of Montana, the north Puget Sound region of northwest Washington state; they have even been observed as far south as Pagosa Springs, Colorado. Historically, they ranged as far south as Texas and southern California. In addition, there is a specimen in the Museum of Comparative Zoology at Cambridge, which was shot by F. B. Armstrong in 1909 at Matamoros, Tamaulipas, Mexico. Since 1992, trumpeter swans have been found in Arkansas each November – February on Magness Lake outside of Heber Springs. These birds feed while swimming, sometimes up-ending or dabbling to reach submerged food. The diet is almost entirely aquatic plants. They will eat both the leaves and stems of submerged and emergent vegetation. They will also dig into muddy substrate 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. Feeding activity, and the birds' weights, often peaks in the spring as they prepare for the breeding season. The young feed on insects, small fish, fish eggs and small crustaceans along with plants initially, providing additional protein, changing to a vegetation-based diet over the first few months. 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. 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 11.8 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 eggs are quite possibly the largest of any flying bird alive today, in comparison they are about 20% larger in dimensions and mass than those of an Andean condor (Vultur gryphus), which attains similar average adult weights, and more than twice as heavy as those of kori bustards (Ardeotis kori). The incubation period is 32 to 37 days, handled 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 of their nest. 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. In captivity, members of this species has survived to 33 years old and, in the wild, have lived to at least 24 years. Young trumpeter swans may have as little as 40% chance of survival due variously to disturbance and destruction by humans, predation, nest flooding, and starvation. In some areas, though, the breeding success rate is considerably greater and, occasionally, all cygnets may reach maturity. Mortality in adults is quite low, usually being 80–100% annually, unless they are hunted by humans. Predators of trumpeter swan eggs include common raven (Corvus corax), common raccoon (Procyon lotor), wolverine (Gulo gulo), American black bear (Ursus americanus), brown bear (Ursus arctos), coyote (Canis latrans), wolves (Canis lupus), mountain lions (Puma concolor), and northern river otter (Lontra canadensis). Nest location can provide partial protection from most mammalian nest predators, especially if placed on islands or floating vegetation in deep waters. Most of the same predators will prey on young cygnets, as will common snapping turtle (Chelhydra serpentina), California gull (Larus californicus), great horned owl (Bubo virginianus), red-tailed hawk (Buteo jamaicensis), red fox (Vulpes vulpes) and American mink (Mustela vison). Larger cygnets and, rarely, nesting adults may be ambushed by golden eagle (Aquila chrysaetos), bobcat (Lynx rufus), and coyote. When their eggs and young are threatened, the parents can be quite aggressive, initially displaying with head bobbing and hissing. If this is not sufficient, the adults will physically combat the predator, battering with their powerful wings and chomping down with their large bills, and have managed to kill predators equal to their own weight in confrontations. Predation of adults when they are not nesting is rare, although they may possibly be hunted by golden and bald eagles as well as Eurasian eagle-owls, wolves, and mountain lions. Photos of a bald eagle (Haliaeetus leucocephalus) exceptionally attacking an adult trumpeter swan in mid-flight were taken recently, although the swan managed to survive the predation attempt.
|
