Cygnus melancoryphus

Geographic Range

Black-necked swans are native to south coastal South America and inland lakes in the Neotropical region. Black-necked swans breed in Patagonia, Tierra del Fuego, and the Falkland Islands. In winter they migrate northward to Paraguay and southern Brazil.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Habitats preferred by black-necked swans are shallow coastal areas along the Pacific Ocean, inland lakes, lagoons, estuaries and marshes. Especially important are areas rich with submergent vegetation. They are recorded from sea level to 1200 m elevation.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• coastal coastal
• brackish water brackish water

• Wetlands
• marsh marsh

• Other Habitat Features
• estuarine estuarine

Physical Description

Black-necked swans are the smallest members of the genus Cygnus , ranging in length from 102 cm to 124 cm. Males range in mass from 4.5 kg to 6.7 kg, and females from 3.5 to 4.4 kg. Wingspan also differs between the sexes, where male wingspan range is 435 to 450 mm, in females it is 400 to 415 mm. Black-necked swans have a relatively high basal metabolism of 3680.56 cm^3 oxygen/hour. Cygnus melanocoryphus has a white body with a distinct long, velvet black neck and head, which distinguishes it from other swans. The neck and head also may have white speckles. The bluish-gray bill has a scarlet base with a large, double-lobed, red caruncle that rests on the base under the eyes. They have a white stripe behind the eyes that extends towards the back of the neck and the windpipe is unconvoluted (has only a slight bend). Black-necked swans have an elevated hind toe, a thin coat of feathers, and pointed wings. The legs are pink, very short, and have unusual positioning, making it hard for these swans to walk on land. The wings are covered in white feathers. Males are usually one-third larger than females, but are monomorphic in shape and color except for their considerably shorter necks. Cygnets (the young) are dull, light brownish-gray in color and have black bills and feet; they obtain their black neck and white body coat in their second year of life.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• male larger

Reproduction

Black-necked swans are monogamous and males and females mate for life. If one of them should die, the surviving mate will find a new mate. Breeding season begins in July and extends to September and November. Swans are known to have triumph ceremonies, which occur when a male attacks a rival suitor, then returns to his potential mate to perform an elaborate courtship ceremony while posturing and calling. Both males and females rhythmically dip their heads into the water and then stretch their necks upwards while swimming around each other. The triumph ceremony has no wing-raising and consists predominantly of calling and lifting of the chin. After copulation, there is no display of mating behavior except for habitual bathing. A nest is built in thick reed beds around the edges of bodies of water. The swan brings material to the site, such as rushes (vegetation) and aquatic plants, in order to build the large structure that partially floats. The cob is quite protective of his pen and her eggs and guards the nest for long periods of time. The monogamous behavior affects the care of cygnets such that the young have been known to ride on their parent's back.

• Mating System
• monogamous monogamous

Black-necked swans breed between July and the autumn months. They can breed as many as three times during the mating season. Clutch sizes range from 3 to 7 eggs, with the mean being 4.6 eggs. It takes between 34 and 37 days for an egg to hatch, with the average being 35 days. Typically, eggs are between 101 x 66 mm in size and weigh approximately 238 gm. Fledging takes place within 10 weeks of hatching and each cygnet stays with its parents for 8 to 14 months before it is independent. Once a cygnet has reached the age of two (average), it is sexually mature and is able to mate. Even though the swans are mature at this age, they do not form pair bonds until they are three years old. Offspring stay with parents until the following summer, and may stay as long as the next winter season.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

During the incubation period, males are very protective of the nest and defend the territory surrounding the eggs. Although both parents are known to carry the young on their backs, the male usually takes over this responsibility after hatching so the female can concentrate on feeding; she must regain the weight she lost during incubation. Both parents provide the hatchlings with food and protection from predators. Females remain very close to cygnets during their foraging. Although vigorous in their use of wings and beak against attack from other animals, black-necked swans panic at the sight of humans and frequently leave their nests without covering their eggs.

• Parental Investment
• precocial precocial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
  • protecting
    • male
    • female
• post-independence association with parents

Lifespan/Longevity

In the wild, C. melancoryphus is expected to live between 10 and 20 years, which a record age of 30 years. In captivity, the average age for a black-necked swan is 6.8 years, but they can live up to 20 years. Typical causes of mortality include disease, predation on cygnets, and lack of food. Black-necked swans also suffer from lead poisoning from incidental ingestion of lead shot from guns used for hunting in the wetlands they inhabit.

Behavior

Black-necked swans are highly social. They are gregarious outside of the breeding season. During the breeding season they become territorial and separate into mated pairs. Despite its gregarious behavior with its own species, the black-necked swan is wary in proximity to humans, where it hides among the reeds and other vegetation. During breeding, they nest in small colonies or in solitaries, but regroup again once their young have hatched, reaching thousands of members to each flock. The flock may move around depending on resources and climate, but generally stay in the southern countries of South America until migration north. Cygnus melancoryphus spends most of its time in the water because walking on land is difficult due to the posterior placement of legs that aid in swimming. While they have difficulty taking flight, they are strong fliers once in the air and can cover long distances; they are one of the fastest fliers of the swan species, and can reach speeds of 50 miles per hour. In a flock, the birds circle each other and call repeatedly while moving the head up and down. If the male needs to defend his territory from another swan or a predator, his aggressive behavior is signaled by lowering the neck and thrusting the head forward. After fighting with a beating of its wings, the black-necked cob triumphantly returned to the female, continuously calling and lifting its chin.

• Key Behaviors
• flies
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• sedentary sedentary
• territorial territorial
• social social

Home Range

Cygnus melancoryphus occupies mainly wet areas due to the difficulty it has with walking. Since it lives in relatively large flocks, the flock's range can span many kilometers either over land when flying, or on water when swimming. Although the flock range is large, each pair of swans claims a territory of 324 m^2 separating the various pairs of mating swans, a considerably smaller area than northern swan species.

Communication and Perception

Courting rituals, flight arrangement, and parental care all use visual communication. Swans signal to other members of the flock or a family unit by dipping the head or flapping the wings to suggest direction or the beginning of a triumph ceremony for mating. This species also uses tactile stimulation to communicate, such as grooming and bathing processes. Females groom young cygnets to teach them how to clean themselves and a bathing ritual is used after copulation to cement the pair-bond. Unlike most other swans, C. melancoryphus does not squawk or honk. Instead they use weak whistles to communicate. Black-necked swans are usually silent, but males give repeated hollow whining sounds, females are more melodious. The typical call for communication is a weak, wheezy whistle uttered both on water and in flight, but does not carry far.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Other Communication Modes
• duets duets
• choruses choruses

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Black-necked swans feed mainly on aquatic vegetation, most often from the bottom of ponds. They have strong bills with serrated edges and a nail at the tip. The surface of the tongue is spinous, which aids in grasping and tearing plants. Also, horny serrations in the bill help to filter small food items from the water surface. This species is mainly vegetarian, feeding mostly on stonewarts ( Characeae ), pondweeds ( Potamogeton ), milfoil ( Myriophyllum ), wild celery ( Vallisneria ), and other waterweeds. They will also eat some invertebrates, like insects and rarely fish or frog spawn.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • algivore

• Animal Foods
• amphibians
• fish
• insects
• other marine invertebrates
• zooplankton zooplankton

• Plant Foods
• leaves
• bryophytes
• algae
• macroalgae macroalgae
• phytoplankton phytoplankton

• Foraging Behavior
• filter-feeding filter-feeding

Predation

Adults have few natural predators, but gulls are a threat to eggs and chicks. Minks and foxes also prey on small cygnets. Humans are considered predators when swans are hunted for food, game, and feathers or quills.

Ecosystem Roles

Two Trichobilharzia species have been found in the nasal cavities of swans, which cause neuromotor problems. Schistosomula of both nasal and visceral Trichobilharzia species are able to develop and migrate for several days in a non-specific mammalian host, so humans are warned not to expose themselves to waters with dense swan populations and probably Trichobilharzia cercaria populations. Other species that use C. melancoryphus as a host are a gape-worm ( Cyathostoma bronchialis ), feather lice ( Mallaphaga ) and roundworm larvae ( Echinuria uncinata ). Gape-worms may cause pneumonia in young birds, often leading to death. Feeding on aquatic vegetation, C. melancoryphus controls algal populations in lakes such that they don't become invasive species in the environment. Black-necked swans may act as a keystone species for the management of these aquatic plants.

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

Swans were a source of food for native peoples of the world, but are seldom hunted currently. Due to the relatively calm nature of C. melancoryphus , they are a valuable breeding bird. There is a large pet trade in this species. Since they have a healthy population in South America and are not endangered, humans have been able to export C. melancoryphus to North America. Also, tourism is highly encouraged to the Falkland Islands just to witness the sight of this species, promoting the tourist industry. Swans control algal populations, improving water quality.

• Positive Impacts
• pet trade pet trade
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

Human microsporidiosis, a serious disease of immunocompetent and immunosuppressed people, can be due to zoonotic and environmental transmission of microsporidian spores. The prevalence of microsporidian infections in waterfowl is significantly higher than in other birds. Waterborne microsporidian spores of species that infect people can originate from common waterfowl, like C. melancoryphus , which have unlimited access to surface waters, including waters used for production of drinking water.

• Negative Impacts
• injures humans
  • causes disease in humans causes disease in humans

Conservation Status

Cygnus melancoryphus populations seem to be stable currently.

Other Comments

Morphological, phylogenetic and molecular data suggests that the Cygnus evolved in Europe or western Eurasia during the Miocene, spreading all over the Northern Hemisphere until the Pliocene. When the southern species ( C. melancoryphus ) branched off is not known.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Dragana Urdarevik (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

References

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