Thursday, Oct 23, 2014

Black-necked Swans

Black-necked Swan, Cygnus melancoryphus

Black-necked Swan The Black-necked Swan (Cygnus melancoryphus) is the largest waterfowl found in southern South America - yet it is the second-smallest swan (the smallest being the Coscoroba Swan).

The Black-necked Swan was previously placed in the monotypic genus, Sthenelides.

The male is called a "cob" - from Middle English cobbe (leader of a group); the female "pen," and their chicks are known as "cygnets" - from the Latin word for swan, cygnus.


Global Names

Chinese: 黑颈天鹅 ... Czech: Labut cernokrká, labuť černokrká ... Danish: Sorthalset Svane ... German: Schwarzhalsschwan ... Estonian: mustkael-luik ... Finnish: Mustakaulajoutsen ... French: Cygne à col noir, Cygne à cou noir ... Irish: eala phíbdhubh, Eala phíbdubh ... Guarani: Ype guasu akâhû ... Italian: Cigno collonero, Cigno dal collo nero ... Japanese: kuroerihakuchou ... Dutch: Zwarthalszwaan ... Norwegian: Svarthalssvane ... Polish: labedz czarnoszyi, łabędź czarnoszyi ... Portuguese: cabeça-preta, capororoca, cisne, cisne-de-pescoço-negro, Cisne-de-pescoco-preto, cisne-de-pescoço-preto, ganso-de-pescoço-preto, pato-argentino, pato-arminho ... Russian: Черношейный лебедь ... Slovak: labut ciernokrká ... Spanish: Cisne cuellinegro, Cisne Cuello Negro, Cisne de cuello negro ... Swedish: Svarthalsad svan ... Turkish: Siyah-boyunlu Kuğu


Black-necked Swan - Cygnus melancoryphus Description

The Black-necked Swan measures 40 - 55 inches (102 – 140 cm) in length (from the top of the head to the tip of tail) and weighs between 10 - 14.8 lbs (4.5 - 6.7 kg). The male is slighter larger than the female.

Males are between 45 - 55 inches (115–140 cm) long and females between 40 - 49 inches (102–124 cm). The males weigh between 10 - 14.8 lbs (4.5 - 6.7 kg), with an average of 12 lbs (5.4 kg). Females weigh between 7.7 - 9.7 lbs (3.5 - 4.4 kg), with an average of 22 lbs (10 kg).

They have a wingspan of about 70 inches (177 cm). The bill is from 2.8 - 3.4 inches (71 - 86 mm) long.

The Black-necked Swan has a long neck and bulky body, and relatively short, set-back legs.

The plumage is mostly white, except for the black head and neck. There is a thin white stripe surrounding the eyes and stretching along the sides of the crown to the rear of the head.

The bill is bluish-grey with a red, double-lobed knob near the base of the bill (known as a caruncle), which usually grows larger on males during the breeding season. The legs are pinkish / flesh-colored.

Gender id:

Males and females look alike, except the male's larger size and the red knob over the base of the bill that is usually larger on males - particularly during the breeding season.

Mobility

Despite the relatively short wings, the Black-necked Swan is a strong and fast flier that can undertake long-distance migrations reaching speeds of up to 50 miles ( 80+ km) an hour. However, they are quite clumsy and not very mobile on land.

Juvenile Description:

The day after hatching, cygnets weigh between 4.6 - 6.4 oz (129 - 184 grams) - with an average of 5.3 oz (150 grams). The plumage is light grey with varying amounts of greyish-flecked and brownish-tipped feathers. The neck and head is more brownish-black. The legs and bill are black. They lack the "knob" at the base of the bill of the adults.

They attain their adult plumage in their second year of life.


Black-necked Swan cygnets, Cygnus melancoryphus Distribution / Range

The Black-necked Swans occur in both saltwater and freshwater habitats -- such as lagoons, freshwater marshes, swamps, lakes and sheltered coastal areas - in southern South America. They are native to the Chile, Argentina; Uruguay, Brazil and Paraguay; and vagrants to the Antarctic Peninsula and Juan Fernández Islands (off the coast of Chile).

The Black-necked Swans breed in Zona Sur (central Chile), Patagonia (Chile and Argentina); as well as Tierra del Fuego (an island group off the southernmost tip of the South American mainland) and Falkland Islands (Malvinas)

They migrate north to winter in Paraguay and southern Brazil.

In Argentina, the Laguna Blanca National Park offers them a protected home.

In Chile, many are found in wetland areas of the Carlos Anwandter Nature Sanctuary located in the Cruces River.

In southeast Uruguay, the Black-necked Swan is most common in Laguna de Roch, where up to 7,000-10,000 Black-necked Swans have been counted.

The Falkland Islands are home to about 200 breeding pairs, which appear to be mostly resident (remaining year-round); except possibly the occasional flights to and from the South American continent.


Black-necked Swans Breeding / Nesting

Swans breed in freshwater marshes, ponds, lakes and along slow-flowing rivers. The Black-necked Swans breed on large freshwater ponds with well-established aquatic vegetation which forms the bulk of their diet.

Most Swans find their mates before the age of 2 years - usually during the winter season. Even though some may nest for the first time when they are two years old, they usually don't start breeding until they are 3 to 7 years old.

Swans are believed to form lifelong pair bonds. However, if one mate dies, the survivor will find another mate. On rare occasions, they may "divorce" - which happens most often after failed nesting attempts.

Upon arrival in the breeding territory, the pair will engage in courtship behavior, which includes bobbing their heads and facing each other with quivering wings.

Nesting usually occurs from July to November.

They will nest in areas with ample food supply, shallow and uncontaminated water, and few disturbances. Usually, only one pair nests on a single body of water. These nesting territories range from 6 to 150 acres in size and are often located near where the female was hatched. The female chooses the nesting area, while the male defends it. Swan pairs are most likely to return to the same nesting site if they were able to raise young successfully there in the past.

Nest

The Swan's nesting season is timed to take advantage of readily available food supplies.

Swans will often place their nests on slightly elevated sites that are surrounded by water, such as small islands, or on top of old beaver houses, dams or muskrat mounds; or on emergent vegetation that is either floating or anchored to the bottom of the water. Pairs will either construct a new nest or repair the nest that they have used in previous years.

Nest-building occurs between August and September and may take up to two weeks. The male uproots aquatic vegetation, grasses and sedges, and transfers it to the female, who will first pile it up high and then uses her body to form a depression to place her eggs in. It's basically shaped like a large open bowl. The interior is lined with down and feathers. Once completed, the nests may reach a diameter of up to 11.5 feet (1 to 3.5 meter). The nest is often surrounded by a 20 to 30 foot (6 to 9  meter) ditch - usually filled with water to make it more difficult for mammalian predators to access the nest.

Eggs / Incubation

The female may start laying eggs before the nest is even completed. Eggs are laid every other day until the clutch is complete. The average clutch consists of 4 to 7 creamy egg. If it is the female's first clutch, she is likely to lay fewer eggs and these eggs are more likely to be infertile.

The egg of a Black-necked Swan is about 3.7 - 4.3 in (93 - 109 mm) long and 2.5 - 2.7 in (63 - 69.3 mm) wide, and weighs from 6 - 9.7 oz (173 to 274 grams).

Once a clutch is complete, the female incubates the eggs for about 36 days, while the male remains nearby to defend the nest against intruders and predators. Very rarely, the male may help brooding the eggs. During the incubation period, the female leaves the nest only for short periods to feed on nearby vegetation, bathe and preen her feathers - however, before doing so, she usually covers the eggs with nesting material to conceal them. The male will also remain nearby to deter predators.

The parents usually perform a "victory display" after intruders are deterred - which is similar to their courtship display and consists of facing each another while quivering their wings and trumpeting loudly. They may lay a second clutch if the first eggs or cygnets are lost.

Cygnets (chicks)

The young - commonly referred to as cygnets - usually start hatching in late October to early November. They emerge from June to July and are covered with down. Their eyes are open, and within 24 hours of hatching, the cygnets are able to leave the nest and another day later, they are able swim and dive under water if needed to escape danger. Hatchlings weigh only about 7 - 10.5 ounces (~ 200 - 300 grams); but they grow quickly gaining 20% of their body weight every day at the early stages. By the time they take their first flight, the cygnets weigh about 15.5 pounds (7 kilograms).

The young are cared for by both parents, who feed and protect them. For the first weeks of their lives, the parents will intermittently brood the cygnets during poor weather and cold spells.

When the cygnets are about two weeks old, they are able to feed themselves, mostly taking aquatic insects and crustaceans (such as crabs, lobsters, crayfish, shrimp, krill and barnacles).

Both parents regularly carry the cygnets (chicks) on their backs mainly as a way of getting them safely to and from their feeding places.

Even though the adult swans only eat plant matter, cygnets initially concentrate on protein-rich insects to support their rapid growth. By the time the cygnets are four to six weeks old, they start changing over to a plant-based diet. By the time they are two to three months old, their diet is similar to the adults' -- mostly consisting of leaves,  stems, tubers, and roots of aquatic plants.

When they are 4 weeks old, the shoulder (scapular), tail and flank feathers are replacing the feather down. At six weeks, the under plumage and cheeks are fully feathered. By seven weeks, they have most neck and head feathers. They are usually fully feathered when they are about 9 - 10 weeks old.

By the time they are 8 to 10 weeks old, they have reached half their adult size and have the juvenile grey plumage that they retain until their second winter.

By the time they are 13 to 17 weeks old, the cygnets usually learn to fly, which often happens in February. Fledglings usually remain close to their parents for continued protection and brooding until the next spring.

Post-Nesting

In late September, the young swans take daily practice flights in preparation for the winter migration. These flights are initially short, but get longer as the young grow stronger.

At the end of the breeding seasons and before the winter migration, the Black-necked Swans undergo a molt during which they lose their flight feathers rendering them flightless for about a month. In Argentina, the molt takes place from November to February.

Swans leave their breeding territories just before the water begins to freeze. Mated pairs or small family groups migrate south to their wintering areas. The young stay with their parents throughout the winter and migrate with them back to their breeding territory in spring. However, when the parents get started on their new brood, they drive their offspring away. At this point, the young swans are about one year old.

The juveniles remain together in sibling groups until they are about two years old, at which time, they themselves commence their search for mates. Some may return to their parents after the breeding season. Their family bonds are generally strong.


Diet / Feeding

What they eat ...

Black-necked Swans feed primarily on algae and aquatic plants. They also eat grain, grasses and crop foods, such as wheat, potatoes and carrots - especially in the winter when other food sources aren't readily available. They may also feed on insects, fish spawn and small invertebrates caught in the water.

Only young cygnets (immature swans) eat aquatic insects and crustaceans, as they have a higher requirement for protein than the adults. As they get older, their diet changes over to a plant diet, which includes aquatic vegetation and roots.

How they eat ...

In shallow water, Swans may use their strong webbed feet to dig into submerged mud and, like mallards, they tip up - plunging the head and neck underwater uprooting plants and snapping off the leaves and stems of aquatic plants.

Cygnets feed on invertebrates and aquatic vegetation stirred up by their foraging parents. Ducks and other water birds also often follow swans to forage on exposed plant matter and aquatic insects.

Swans also forage by swimming picking up plant material from the water's surface or water's edge. On land, they feed on grains and grasses.


Lifespan

Black-necked Swans can live from 10 to 30 years. Captive birds average 7 years; although some have made it to 20 years.


Calls / Vocalizations

Unlike most swans that are known for their loud calls, the Black-necked Swan - like its nearest relatives the Black and Mute Swan - is relatively silent, except for soft, musical whistling notes repeated several times, particularly during flight.


Status

Black-necked Swans are widespread and common throughout its habitat, and is evaluated as Least Concern on the IUCN Red List of Threatened Species (listed on Appendix II of CITES).

However, environmental pollutants have caused the loss of thousands of Black-necked Swans in 2004 and 2005 in the Carlos Anwandter Nature Sanctuary in Chile due to a major contamination by Valdivia Pulp Mill located on the Cruces River which feeds the wetlands.

Species Research by Sibylle Johnson

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