A Symphony of Swans
Because of their immaculate white plumage and their strong pair and family bonds, swans have also long served as icons of beauty, devotion, and longevity in the myths and folklore of many cultures. Our personal interests in and perceptions of wild swans are often formed in childhood, by reading such classics as Hans Christian Anderson’s stories “The Ugly Duckling” and “The Wild Swans” or E. B. White’s The Trumpet of the Swan or perhaps upon seeing a performance of Tchaikovsky’s Swan Lake ballet.
Many of the most admired human traits, such as permanent pair bonding, extended biparental care, and family cohesion, are biological facts in swans, but the sadly romantic idea of a dying swan uttering a final “swan song” is only folklore. Yet a famous American biologist, D. G. Elliott, reported in 1898 that once, after he had shot and wounded a whistling swan in flight, it began a long glide while uttering a series of “plaintive and musical” notes that “sounded at times like the soft running of the notes of an octave” as it gradually drifted downward. Nowadays such unusual behavior would probably be interpreted as only an instinctive distress call, but Elliott’s story might have provided an early factual basis for this commonly used expression.
Most Americans are probably personally familiar with the regal-looking mute swan of Europe, which has long been imported to American parks and zoos. Mute swans have also long been used by wealthy landowners to decorate private ponds and help control the growth of unwanted aquatic plants. When mute swans escaped from Long Island estates during hurricanes in the late 1930s, many became feral, and their offspring have since expanded over much of the Atlantic coast, from New Hampshire south to the Carolinas. Following introductions dating back to 1919, mute swans have also spread out from the eastern shoreline of Lake Michigan, occupying much of the Great Lakes region from Wisconsin to New York, and are now considered an invasive species in several states. A few seemingly wild mute swans have been seen recently in Nebraska, but the evidence as to their origins is still too murky to add them to the official list of Nebraska birds.
Two other swans of comparable beauty but unquestionably wild origins can be seen in Nebraska. Unlike the virtually silent mute swan, both of our native American swans have loud, clarion voices that were the historic basis for their English names, whistling swan and trumpeter swan. The smaller (up to twenty pounds) whistling swan, now officially called the tundra swan, has a musical, more soprano-like, voice, while the trumpeter’s is louder and more baritone-like. During the 1980s the English name tundra swan officially replaced whistling swan, to describe its high-arctic breeding habitat and to include within the same species its close Eurasian relative, the Bewick’s swan.
The trumpeter swan is a substantially larger species, with adults sometimes reaching thirty pounds, making it the heaviest of American birds. It too has a very close and slightly smaller Eurasian relative, the whooper swan, but so far these have been considered biologically distinct species. All four of these swans have loud, clarion voices and often use them in long-distance communication and territorial interactions.
These vociferous swans are also notable among waterfowl in having windpipes (tracheae) that penetrate the bony breastbone and form a long internal loop within it. Just before the windpipe enters the lungs, it is transformed into a bony sound box (the syrinx) with paired vibratory membranes that are set into motion when the lungs expel air. Varied tensions on the paired membranes influence the rate of their vibrations. This vibration rate sets the basic frequency of the resulting sounds that, because of subvibrations, produce additional overtones (harmonics) that enrich the vocalizations. The windpipe further modulates and amplifies particular sound frequencies, depending largely on its volume and length, enhancing harmonic complexity. These remarkable adaptations in trumpeter and tundra swans allow for a great range of individual vocal variations and a high degree of harmonic development, making every individual swan’s voice unique and probably easily recognizable by others. Very similar structural adaptations are present in whooping and sandhill cranes and produce similarly loud and individually identifiable vocalizations.
As high-arctic nesters, tundra swans appear in Nebraska only during spring and fall migrations. During fall migration, those swans breeding in the central Canadian Arctic fly south to North Dakota, gradually veering toward the east as they approach South Dakota. The swans then follow a southeastern route roughly paralleling the Minnesota River Valley and from there continue eastward to wintering areas that extend from Chesapeake Bay south to the Carolinas.
This diagonal migration route means that only in northeastern Nebraska is one likely to encounter tundra swans, while they pass southward during November–December and return in March–April. However, in North Dakota and eastern South Dakota tundra swans are sufficiently common that so-called sport hunting is permitted. At least four thousand tundra swans of the eastern North American population are legally killed annually in the Dakotas, North Carolina, and Virginia. Several thousand more are killed by poachers or are wounded but never retrieved, with the total kill probably approaching ten thousand birds annually, or perhaps 10 percent of the eastern population.
Swans from the western population that breeds in western Canada and Alaska take a different fall migration route, which passes from Saskatchewan and eastern Alberta southwest through Montana, Utah, and Nevada and then on to California wintering grounds. Like the eastern flock, the western North American population probably numbers at least one hundred thousand birds, and they can be legally hunted in states such as Montana, Utah, and Nevada. Hunting in those states, plus subsistence hunting by Natives in Alaska, probably results in the deaths of at least ten thousand swans annually, also about 10 percent of the total western population.
Luckily, America’s largest swan, the trumpeter, is fully protected. It was on the list of federally endangered species for many years and was not removed from that list until it became apparent that a large and previously unstudied population of swans in southern Alaska are actually trumpeter swans rather than tundra swans. Additionally, since the 1960s great efforts have been made to relocate trumpeter swans from surviving populations in the Rocky Mountain region to historical breeding areas of the northern Great Plains, substantially increasing the species’ total population, which by 2012 numbered over forty-six thousand birds.
Nebraska’s historic breeding trumpeter swans were extirpated by 1900 but were later reestablished during the 1960s as a result of releases of cygnets at Lacreek National Wildlife Refuge, South Dakota. Restoration efforts there, at the northern edge of the Sandhills, were so successful that by 1987 the population had reached nearly 300 individuals. Expansion southward into the Nebraska Sandhills followed, so that by 1999 there were nearly 600 records for the Nebraska Sandhills, with Cherry and Garden Counties accounting for about 70 percent of the total, as well as 160 nesting records. Nesting now occurs in many Sandhills lakes and large, shallow marshes. Additionally, some spring-fed streams of the Sandhills, such as the North Loup River and Blue Creek, usually remain unfrozen all winter, eliminating the need for long seasonal migrations. The current Nebraska breeding population probably numbers several hundred.
Trumpeter swans mate permanently, and each pair returns to its nesting area in spring as soon as the weather allows. Nesting marshes in Nebraska are typically large, shallow, and well vegetated, with abundant shoreline plants and submerged aquatic vegetation. Marshes having muskrat present are favored, as their “houses” provide a convenient nest substrate, protected from most wave action. Nesting territories average more than thirty acres and sometimes exceed one hundred acres. They are vigorously defended, the adults even excluding their own offspring from previous years. The male performs most territorial defense, but after territorial disputes the female participates in “triumph ceremonies” that are marked by loud mutual calling and wing waving. She also helps defend the nest site when needed.
Both sexes help construct the often-bulky nest, which may simply be the flattened top of a muskrat house or may consist of piled-up reeds and bent-down emergent vegetation that provide an elevated platform. Nesting behavior in the Sandhills has been seen as early as April 28. The eggs (typically four to six) are then laid at two-day intervals, with incubation starting only after the clutch is complete. The female performs most incubation over the thirty-two-to-thirty-seven-day period to hatching, while the male patrols the territory.
Hatching in Nebraska is likely to occur during late May or early June. The cygnets hatch within a few hours of each other and are led from the nest within twenty-four hours of hatching. The cygnets’ fledging period to initial flight is approximately one hundred days, which means that the brood’s first flights might not occur until September. The cygnets remain with their parents for at least their first year of life but are evicted from the nesting territory by the following spring. From four to seven years might pass before the young birds begin to breed, although sexual maturity is reached much sooner.
As a protected species, trumpeter swans often live for ten years or more and are known to have survived for at least twenty-four years. Wild tundra swans appear to have somewhat shorter life expectancies that rarely exceed ten years, perhaps in part because of hunting-related mortality, their much longer and more stressful migration routes, and the rigors of arctic nesting.
Some of the places along Nebraska highways where trumpeter swans can usually be seen during summer are on larger marshes off U.S. Highway 2 in Grant and Sheridan Counties, at a wetland off the South Loup River at the southern edge of Ravenna, and near U.S. Highway 83 in Cherry County, between Valentine and Valentine National Wildlife Refuge. In 2011 four pairs produced eleven cygnets at Valentine National Wildlife Refuge, making it one of the state’s premier swan-breeding sites.
Continued releases of trumpeter swans in the Midwest, especially in Minnesota, have greatly increased the chances of seeing trumpeter swans in the region. By 2012 there were perhaps ten thousand trumpeter swans in the eastern North American population, breeding from South Dakota and Iowa east to Ontario. Because of highly successful restoration efforts in Minnesota (with a 2012 population of fifty-five hundred birds), thousands of trumpeter swans migrate through Iowa each spring and fall, supplementing that state’s own recently established population of breeding birds. Some of the places in Iowa where migrating trumpeter and tundra swans can usually be seen include Forney Lake Wildlife Area near Thurman, Union Slough National Wildlife Refuge near Bancroft, and the Upper Mississippi National Wildlife and Fish Refuge near McGregor.
One of the increasingly important regional wintering areas for trumpeter swans near Nebraska is Squaw Creek National Wildlife Refuge, near Mound City, Missouri. From November through winter as many as 456 swans have been seen, as well as up to a half million or more migrating snow geese and countless other waterfowl. It provides a visual spectacle that one is likely to remember and cherish for a lifetime.