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Trumpeter Swan

Trumpeter SwanThe Trumpeter Swan (Cygnus buccinator) was once common throughout North America. By the 1900s, however, a combination of habitat destruction and hunting led the species to near extinction. In 1978, Trumpeter Swans were listed as a vulnerable species in Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Fortunately, efforts to recover Trumpeter Swans have been undertaken throughout many parts of its former range and almost all swan populations have increased in the latter half of this century. Trumpeter Swans are no longer listed as a species at risk by COSEWIC (1999) but are still considered a threatened animal under the Alberta Wildlife Act.

Summer habitat for the Trumpeter Swan varies widely throughout its range. In Alberta, trumpeters live in scattered flocks on lakes and marshes in the Aspen Parkland and Boreal Natural Regions. The basic breeding habitat requirements for the Trumpeter Swan being adequate room to take off (approximately 100 metres), accessible forage, shallow, stable levels of unpolluted fresh water, emergent vegetation, a muskrat house, island or other structure for the nest site, and low human disturbance. Similarly, Trumpeter Swan nesting lakes in Alberta generally have at least five common characteristics: lake water levels do not have marked seasonal fluctuations; the waters are quiet, without strong wave action or currents; shallow water so the swans can dig for tubers and roots of aquatic plants; isolation and security from human disturbance; and areas of emergent vegetation. Nests are rarely located in upland areas but are usually located near shore, on small islands, or on muskrat and beaver lodges. Habitats supplying high abundance of aquatic invertebrates and/or aquatic plants have the greatest swan production.

Trumpeter Swan during winterMost of Alberta's Trumpeter Swans winter in the United States in the tri-state area where the borders of Montana, Idaho and Wyoming meet. Weather is the greatest single factor affecting winter distribution and survival in this area as temperatures can reach -45 degrees Celsius, and snow accumulations average 250-380 centimetres. Trumpeter Swans survive in these harsh conditions because a combination of complex geological formations and weather patterns in the area create mild microclimates. Almost annually, a midwinter thaw occurs that lasts from one to two weeks and opens up water that may otherwise freeze.

Trumpeter SwanThe Trumpeter Swan is North America's largest native waterfowl, with females weighing an average of 9.9 kilograms and males weighing an average of 10.3 kilograms. These swans are completely white except for their black bills and legs, and are easily mistaken for the slightly smaller Tundra Swan. Some subtle morphological differences exist between the species (for example, most Tundra Swans possess a yellow spot in front of the eye), but the only consistent difference between Trumpeter and Tundra Swans is their voice; Trumpeter Swans have a deep trumpet-like call, whereas Tundra Swans have a high-pitched "bark".

Canadian Trumpeter Swans wintering in the tri-state area leave for their breeding grounds between March 1st and April 1st. The initial pair bonds are formed from late March to mid-May. Trumpeter Swans pair with life-long mates as early as their second winter, and most swans are paired by the end of their third winter. Despite this early pairing, the average age of first reproduction by Trumpeter Swans in Alberta is five years.

Trumpeter Swans arrive in Alberta in mid-April to early May. Nest building occurs between late April and early May and breeding density is generally one pair per lake or pond. Nests are used for many years, and take several days to two weeks to build. A typical Trumpeter Swan nest is comprised of cattails, bulrushes and horsetails lined with down. The nest is often built on a beaver lodge, muskrat house, small island, or on a floating mat of vegetation, and the adults may remove vegetation from around the nest to provide good visibility and protection from predators.

Clutches of 3-9 eggs are laid and the female undertakes most of the incubation duties. When the incubating female takes a break to feed, the eggs are covered carefully with grass and down, presumably to provide insulation and to make the eggs less visible to predators. While the female is incubating, the male feeds and defends the territory. The female will help the male defend the territory, but extended absences from the nest may lower incubation success, as eggs may either overheat or become cool.

Trumpeter Swan with cygnetsOnce the cygnets hatch, the adults will rarely venture more than 20 metres away. Cygnets feed almost exclusively on aquatic invertebrates and crustaceans for the first 2-5 weeks after hatching. By the age of 2-3 months, however, a cygnet's diet is the same as an adult's, and consists of stems, roots and shoots of horsetail, pondweed, sedges, and other plant material. Both adults and cygnets spend most of their time feeding in emergent vegetation, and adults may eat up to 9 kilograms of food per day. This massive food requirement is one reason the density of swans is limited to one swan family per lake.

Growth of cygnets is rapid, and by 13-15 weeks, most cygnets have had their first flight. In mid-September, Trumpeter Swans stage on larger lakes before migrating to wintering areas. In Alberta, most swans begin to migrate south by mid-October, however some swans remain as late as mid-November.

Mortality for Trumpeter Swans is highest during the first year of life. Survival of cygnets during the pre-flight period has been reported at 45-78%.  Sources of mortality include predation, disease and parasites, weather, lead poisoning, accidental shooting and electrocution on power lines. Predation is not considered to be a major source of mortality, but birds of all ages (including eggs) may be taken by a variety of avian and mammalian predators. Diseases and parasites are potential sources of mortality, but not significant on their own. Nasal leeches in trumpeters wintering in the tri-state area can be a direct cause of death in cygnets and can weaken adults. Thus, a high parasite load in the winter may make certain individuals more susceptible to severe winter weather.

Reprinted from Alberta Wildlife Status Report No. 26 (2000), with permission from Alberta Sustainable Resource Development.

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