Classification and Range
Coscoroba swans are part of the order Anseriformes, in the family Anatidae (ducks, geese, swans). In the genus Coscoroba, there is just one species: C. coscoroba. Coscoroba swans live in the southern part of South America, in the countries of Chile, Argentina, Uruguay, southern Paraguay and southern Brazil. Southern populations migrate northward and spend the winter in northern Argentina, Uruguay and southeast Brazil. Those populations that live in the central part of their range likely remain sedentary.
Prefers shallow areas of fresh water, such as ponds, lagoons, canals and swamps with sufficient vegetation for cover. Coscoroba swans normally live at low elevations, but researchers have documented them living at elevations as high as 3,300 feet (1000 m) or more.
While coscoroba swans are the smallest species of swan, they are still a large bird. Males and females can only be differentiated by size. Males are longer, heavier and have a wider wingspan. Males and females have a body length of 34.6 – 45.2 inches (88 – 115 cm). Males weigh 8.4 – 11.9 pounds (3.8 – 5.4 kg) and have a wingspan of about 18.9 inches (48 cm). Females weigh 7 – 10 pounds (3.2 – 4.5 kg) and have a wingspan between 17 – 18 inches (43 – 46 cm).
Adult females and males are identical in coloration. White feathers cover almost their entire body, except for six black primary feathers that appear as black tips on the end of their wings but are more visible in flight. The end of the tail may also have black feathers. Juvenile coloration is duller than adults, usually white with patches of gray-brown on the head, back and wings.
The bill, legs and beak are a brilliant waxy-red, bright pink or orange color. The bill is flattened and 2.5 – 2.7 inches (6.3 – 6.8 cm) in length. Inside the bill, there are serrated comb-like structures called lamellae, which help filter food. When eating, swans scoop up water and food, hold it in their mouth and squeeze out the water through the lamellae. Also inside the upper bill is a hard, horny tip (known as the "nail") that assists with breaking open mollusks. Depending on the individual, the eyes can be a variety of colors, from yellow, orange, red to brown. Juveniles have blue-gray or red-gray legs and bill.
Their legs are strong, fully scaled and the three front toes are fully webbed. The rear toe is less pronounced and is farther up the back of the leg.
Coscoroba swans walk awkwardly on land, as their short legs result in a clumsy waddle. Wings are relatively short, strong and pointed. To become airborne from the water, swans have large and well-developed wing muscles that join at the sternum and lend the birds their broad breast. To fly, they beat them continuously and quickly in order to gain or maintain momentum in the air. They only glide when landing.
In the wild, they live an average of 7 years but can reach 20 years of age. In zoos, they can live up to 35 years.
In the wild: various plant matter, small aquatic invertebrates (mollusks, crustaceans and insects) and small fish.
At the zoo: romaine lettuce and waterfowl pellets.
Breeding occurs October – December. Courtship displays take place during this time and the male performs a unique series of movements designed to woo the female. Courtship displays in subsequent years for returning pairs are less elaborate and more resemble ritualized movements at lower intensity. After the male and female form a pair, they nest alone or in small groups. Coscoroba swans often mate with the same partner for life. Cases of separation are rare, but sometimes occur, particularly following nesting failure. If one of a pair dies, the survivor usually takes a new mate and remains devoted to their new partner. These pair bonds are essential in maintaining the same territory year after year.
Mating takes place in the water and the male bites the neck of the female while making additional loud, distinct calls. During breeding season, the call serves many purposes: it occurs during the many stages of courtship, mating and serves to defend the territory once the male and female have mated. The pair chooses a nest site with quick access to the water or direct access from the air. Nests are complex and bulky compared to other members of Anseriformes, consisting of large amounts of plant material built in a conical mound. The male builds the nest on a small island, amongst reeds or partially floating on the edge of a waterway in long grass. On top of this mound is a shallow depression in which the female lines the nest with soft grasses and her own feathers.
The female lays three to nine eggs at one day intervals in the nest. Eggs are a white-cream color, 3.2 – 3.7 inches (8.2 – 9.4 cm) in length, 2.1 – 2.6 inches (5.3 – 6.7 cm) wide and 4.6 – 7.2 ounces (129 – 203 g) in weight. The eggs are so large that they represent 20% – 30% of the female's body weight. The male does not bring food to the female, so she must leave the nest to eat. Males do not incubate while the female is absent. Instead, the female covers the nest to keep the eggs warm and hide them from predators while she is away. Against all but the largest and boldest predators, male swans are aggressive defenders of their chosen territory. Females defend only the nest-site, but more vigorously with direct attacks on intruders.
Incubation lasts 33 – 40 days, and all the eggs hatch at once. A few days before hatching, the chicks begin calling to their parents from inside the eggs. At birth, the chicks (called cygnets) are very small and weigh just 3.5 – 4.2 ounces (99 – 119 g). Cygnets are silver-gray or brown, with three darker gray stripes on their back and other black coloring on their head. Their bill is gray, edged with pink and the legs are pale pink tinged with gray.
Cygnets are precocial and within a few hours of birth, are able to swim and easily find food on their own. Both the male and female rear the young. Despite the porous appearance of cygnets' down, it is fully waterproofed and they freely dive for their food. Rather than feed the chicks in the nest, the parents lead them to suitable feeding areas and guard them from predators. Parents may use their feet to stir up food from the bottom to the surface for the chicks to feed. For the first few weeks, cygnets mainly eat small invertebrates and small crustaceans. The flightless young are a source of food for small predators, birds of prey and gulls. Despite the parents' fierce defense of their cygnets, mortality is high and as much as 80% of the chicks do not survive the first 12 months of life.
After the breeding season, the parents molt all of their flight feathers at once and become flightless for three to four weeks until new feathers emerge. During the molt, coscoroba swans gather in large flocks for protection.
For the cygnets, fledging can occur as quickly as 60 – 75 days after hatching, but normally takes until the cygnets are 3 – 4 months old. Throughout the winter, cygnets remain with their parents and then migrate with them to breeding grounds. If they do not migrate, the adult pair spurns their juveniles as they prepare for the next brood. Cygnets take eight months to reach adult size. Females and males do not breed until they are at least 3 years old and perhaps as old as 5 years of age for males.
Swans have spectacular contact calls, on the water or in the air. Special structures in their throat act as resonating chambers to produce loud, trumpet-like sounds. The first syllable is longer and higher in pitch than later syllables and females call in an even higher pitch than males. While taking care of their young, both females and young have lower-pitched tones. While together, they announce these repeatedly to each other. Young cygnets remain near their mother but may swim off in search of their own food. If this signal-calling is interrupted, this causes alarm and the female quickly gathers her chicks together for protection. The female may also sound a short, high-pitched alarm call, causing the chicks to seek cover amongst shoreline vegetation. The chicks wait silently and motionless until the mother resumes her contact calls.
Swans choose their habitat based on the depth and quality of water, amount of protective vegetation and presence of food. At night, they roost on the water or on undisturbed islets near the shore. While sleeping, they tuck their bill underneath their wing feathers.
Coscoroba swans feed by dabbling or grazing on the surface of the water for plants and algae. Swans eat not only the greener part of plants, such as leaves, buds or stems, but also the seeds, roots and tubers. They may also eat small stones or sand to assist with digestion of tough plant materials. They eat by inserting their head, neck and sometimes the front half of their body underwater to upend aquatic plants. Occasionally, the necks and faces of coscoroba swans become stained from the mud or other minerals in the water. They may also graze on young plants along the shoreline or in waterside pastures.
Swans have a thick covering of feathers to insulate them from the water. Every day, they spend many hours preening their feathers to keep them in good condition. In addition to preening themselves, they may preen others; mutual preening reinforces social bonds. Preening involves two paired actions: thorough combing of all feathers to remove dirt and water, then coating them in an oily substance from their highly developed oil-gland located at the base of the tail. This maintains waterproofing..
Safety in Numbers
Coscoroba swan are relatively sociable within their own species and with other waterfowl. Flock size varies from a few dozen individuals to hundreds or more, depending on season and location. Outside of the breeding season, these swans live in flocks of less than 100 birds. Living in large flocks enables coscoroba swans to find the best feeding sites, learn migratory routes and avoid predators. Birds within the flock take turns watching for predators and are ready to warn the others.
When migrating, the flock maintains visual contact as much as possible and will call out to each other to stay united during inclement weather or poor lighting conditions. During migrations, coscoroba swans may fly with flamingos or black-necked swans (C. melanocoryopha). Migration routes may take place at extreme elevations; researchers have noted swans flying at elevations of 26,277 feet (8,000 m). These high altitudes allow the birds to take advantage of stronger air currents. Additionally, swans almost always fly in a V-formation to save energy, as the bird in front creates a slipstream for the bird behind it to fly through.
Goose, Duck or Swan?
The coscoroba swan is a puzzle for many taxonomists. Externally, the body, head and legs appear to be more like a goose than a swan. As an example, their body is much smaller in comparison to other species of swans; the largest species average double the weight and have a wingspan at least 40% larger. Since they are smaller in size compared to other swan species, coscoroba swans require shorter distance to lift off from the ground or water. In contrast to other species of swan, coscoroba swans have a shorter neck and longer legs. Another feature that distinguishes coscoroba swans from other species is that feathers cover their facial skin, instead of bare skin extending from the bill to the eye. This species also lacks the characteristic basal knob found on all other five species of swans. Compared to other swans, the bill of a coscoroba swan is smaller and more resembles the bill of a duck.
Furthermore, the vocalizations of coscoroba swans more closely resemble that of geese. Also dissimilar to typical swans, coscoroba swans do not have a 'triumph ceremony.' This term refers to the performance a male gives to his potential mate after attacking a rival suitor; it is an elaborate ceremony involving posturing and calling. Unlike swans in the genus Cygnus, coscoroba swans do not carry cygnets on their back. Lastly, coscoroba swans are also the only species of swan with cygnets that look like young whistling ducks. Some scientists believe that coscoroba swans are either the genetic link between swans and true geese, or between swans and whistling ducks, or both!.
Location at the Zoo
Look for a coscoroba in the flamingo exhibit in the zoo's Temperate Forest zone.
While coscoroba swans are listed on Appendix II to the Convention on International Trade of Endangered Species of Flora and Fauna (CITES), they are not an endangered species. A listing on Appendix II means that they are not presently threatened with extinction but may become so if their populations are not monitored. However, they are listed as one of 10 endangered bird species in Chile, where less than 1,000 individuals live in the extreme southeast portion of that country. Additionally, at least 27 other species of waterfowl in Anseriformes are either vulnerable, endangered or critically endangered. Coscoroba swans have a large range elsewhere within South America, as their stable populations cover at least 965,000 square miles (2.5 million km2) with a minimum population of at least 10,000 and up to as many as 25,000.
The biggest threats to coscoroba swans (and many other species of waterfowl) are loss of habitat and other human–caused activities. These activities include drainage of wetlands for agriculture, housing, logging and construction of roads. When migrating, coscoroba swans also collide with power lines or other human–made structures. They also accidentally eat lead pellets fallen in the water from gunshots, or lead fishing lures stuck in fish. Further affecting their survival is the spread of bird flu; all six species of swans are affected by and can catch H5N1 (avian influenza). Fortunately, coscoroba swans may be able to adapt to these impacts by foraging in and eventually settling in areas of human development. For example, coscoroba swans can colonize new bodies of water formed by the completion of dams or irrigation projects. These swans are important in maintaining and controlling the growth of aquatic vegetation. Without them, waterways would become clogged and more localized flooding would occur.
Humans have hunted swans for centuries. Specifically, the trumpeter swan once lived throughout North America but nearly became extinct in the 1900s. Humans collected their eggs for food and killed them for feathers, skin and meat. Fortunately, this species has recovered from just 69 birds in 1932 to more than 10,000 recently. One species of swan was not so fortunate; the Chatham swan (C. sumnerensis) of New Zealand became extinct sometime between 1590 and 1690 by natives that hunted them for food.
One organization seeks to develop and maintain an international network of wetlands. The International Waterfowl and Wetlands Research Bureau (IWR) created the Convention on Wetlands. This is an intergovernmental treaty that facilitates national action and international cooperation for the conservation and use of wetlands. In 1971, the IWR established the Ramsar List, which identifies and protects "internationally important wetlands." A wetland is deemed important if it regularly supports 20,000 or more waterbirds. Currently, the Ramsar List provides protection for potential coscoroba swan habitat in 40 sites totaling more than 29 million acres (11.7 million ha). At present, there are more than 1,000 sites on the List and the objective is to have at least 2,500 sites on the List by 2010. Wetlands are important for the conservation of global biological diversity, as they perform a variety of valuable ecological and hydrological functions. By protecting them, wetlands will also sustain human life.
How You Can Help!
The effort to save endangered species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Please do not buy products made from wild animal parts. Contact your elected representatives and express your views about conservation of endangered species and wild habitats.
Contact Woodland Park Zoo at firstname.lastname@example.org to find out how you can support conservation efforts at the zoo. Learn other ways you can help conserve wildlife and the habitats they require for survival by visiting our How You Can Help page.
Sources and Suggested Reading
Bourne, Debra. Date unknown. Coscoroba coscoroba. Wildlife Information Network. Accessed March 1, 2008 at http://wildlife1.wildlifeinformation.org/List_Vols/Wildpro_Gen_Cont.htm.
del Hoyo, Josep et al. 1992. Handbook of the Birds of the World, Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain. 696 p.
Jimenez, Mariano G. and Mariano Jimenez II. 2007. Coscoroba Swan. Zoo Damisela. Accessed March 1, 2008 at http://www.damisela.com/zoo/ave/otros/indexe.htm.
Johnsgard, Paul A. 1978. Ducks, Geese, and Swans of the World. University of Nebraska Press, Lincoln NE. 391 p.
Scott, Peter. 1972. The Swans. Houghton Mifflin, New York, NY. 242p.
Seaworld/Busch Gardens Animal Bytes: Coscoroba Swan. Accessed March 1, 2008 at http://www.seaworld.org.
Todd, Frank S. 1997. Natural History of the Waterfowl. Ibis Publishing, San Diego, CA.
The Trumpeter Swan Society at http://www.trumpeterswansociety.org.
Utah's Hogle Zoo Animal Database: Coscoroba Swan. Accessed March 1, 2008 at http://www.hoglezoo.org.
Wilmore, Sylvia B. 1974. Swans of the World. Taplinger Publishing, New York, NY. 229 p.
Woolhead, Jan. 1984. Coscoroba coscoroba. Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) species identification manual. Accessed March 1, 2008 at http://www.cites.org/eng/resources/ID/.