The trumpeter swan (Cygnus buccinator) is a species of swan found in North America. The heaviest living bird native to North America, it is also the largest extant species of waterfowl, with a wingspan of 185 to 250 cm (6 ft 2 in to 8 ft 2 in).[2] It is the American counterpart and a close relative of the whooper swan (Cygnus cygnus) of Eurasia, and even has been considered the same species by some authorities.[3]
By 1933, fewer than 70 wild trumpeters were known to exist, and
extinction seemed imminent, until aerial surveys discovered a Pacific
population of several thousand trumpeters around Alaska's Copper River.[4] Careful reintroductions by wildlife agencies and the Trumpeter Swan Society gradually restored the North American wild population to over 46,000 birds by 2010.[5]
Description
Its black bill is useful in distinguishing the trumpeter swan from the introduced
Mute swan.
[6]The trumpeter swan is the largest extant species of waterfowl, and
both the heaviest and longest native bird of North America. Adults
usually measure 138–165 cm (4 ft 6 in – 5 ft 5 in) long, though large
males can exceed 180 cm (5 ft 11 in) in total length.[2][7][8][9]
The weight of adult birds is typically 7–13.6 kg (15–30 lb). Possibly
due to seasonal variation based on food access and variability due to
age, average weights in males have been reported to range from 10.9 to
12.7 kg (24 to 28 lb) and from 9.4 to 10.3 kg (21 to 23 lb) in females.[2][10][11][12]
It is one of the heaviest living birds or animals capable of flight,
and, in terms of average mass, the heaviest flying bird in the world.
Alongside the mute swan (Cygnus olor), Dalmatian pelican (Pelecanus crispus), kori bustard (Ardeotis kori), and Andean condor (Vultur gryphus),
it is one of a handful to weigh in excess of 10 kg (22 lb) between the
sexes, and one survey of wintering trumpeters found it averaged second
only to the condor in mean mass.[13][14] The trumpeter swan's wingspan ranges from 185 to 250 cm (6 ft 1 in to 8 ft 2 in), with the wing chord measuring 60–68 cm (24–27 in).[2][7][8][15]
The largest known male trumpeter attained a length of 183 cm (6 ft
0 in), a wingspan of 3.1 m (10 ft 2 in) and a weight of 17.2 kg (38 lb).
It is the second heaviest wild waterfowl ever found, as one mute swan
was found to weigh a massive 23 kg (51 lb), but it was unclear whether
the latter swan was still capable of flight because of its bulk.[16]
The adult trumpeter swan's plumage is entirely white. Like mute
swan cygnets, the cygnets of the trumpeter swan have light grey plumage
and pinkish legs, gaining their white plumage after about a year. As
with the whooper swan, this species has upright posture and generally
swims with a straight neck. The trumpeter swan has a large, wedge-shaped
black bill that can, in some cases, be minimally lined with salmon-pink
coloration around the mouth. The bill, measuring 10.5–12 cm (4.1–4.7 in), is up to twice the length of a Canada goose's (Branta canadensis)
bill and is the largest of any waterfowl. The legs are gray-pink in
color, though in some birds can appear yellowish gray to even black. The
tarsus measures 10.5–12 cm (4.1–4.7 in).
The mute swan,
introduced to North America, is scarcely smaller. However, it can
easily be distinguished by its orange bill and different physical
structure (particularly the neck, which is typically held curved as
opposed to straight in the trumpeter). The mute swan is often found
year-around in developed areas near human habitation in North America,
whereas trumpeters are usually only found in pristine wetlands with
minimal human disturbance, especially while breeding.[2] The tundra swan (C. columbianus)
more closely resembles the trumpeter, but is significantly smaller. The
neck of a male trumpeter may be twice as long as the neck of a tundra
swan.[2] The tundra swan can be further distinguished by its yellow lores. However, some trumpeter swans have yellow lores; many of these individuals appear to be leucistic and have paler legs than typical trumpeters.[17]
Distinguishing tundra and trumpeter swans from a distance (when size is
harder to gauge) can be challenging without direct comparison but it is
possible thanks to the trumpeter's obviously longer neck (the great
length of which is apparent even when the swan is not standing or
swimming upright) and larger, wedge-shaped bill as compared to the
tundra swan.
Trumpeter swans have similar calls to whooper swans and Bewick's swans. They are loud and somewhat musical creatures, with their cry sounding similar to a trumpet, which gave the bird its name.
Range and habitat
Approximate summer range of the three regional populations of trumpeter swans in North America
Beginning in 1968, repeated in 1975, and then conducted at 5-year
intervals, a cooperative continental survey of trumpeter swans was last
conducted in 2015.[5]
The survey assesses trumpeter swan abundance and productivity
throughout the entire breeding ranges of the three recognized North
American populations: the Pacific Coast (PCP), Rocky Mountain (RMP), and
Interior (IP) populations (see Figure). From 1968 to 2010 the
population has increased from 3,722 to approximately 46,225 birds, in
large part due to re-introductions to its historic range.[5]
Their breeding habitat is large shallow ponds, undisturbed lakes,
pristine wetlands and wide slow rivers, and marshes in northwestern and
central North America, with the largest numbers of breeding pairs found
in Alaska.
They prefer nesting sites with enough space for them to have enough
surface water for them to take off, as well as accessible food, shallow,
unpolluted water, and little or no human disturbance.[18] Natural populations of these swans migrate to and from the Pacific coast and portions of the United States, flying in V-shaped flocks. Released populations are mostly non-migratory.
In the winter, they migrate to the southern tier of Canada, the eastern part of the northwest states in the United States, especially to the Red Rock Lakes area of Montana, the north Puget Sound region of northwest Washington state;[19] they have even been observed as far south as Pagosa Springs, Colorado. Historically, they ranged as far south as Texas and southern California.[20] In addition, there is a specimen in the Museum of Comparative Zoology in Cambridge, Massachusetts, that was shot by F. B. Armstrong in 1909 at Matamoros, Tamaulipas, Mexico.[21] Since 1992, trumpeter swans have been found in Arkansas each November – February on Magness Lake outside of Heber Springs.[22] In early 2017, a juvenile trumpeter swan took up residence in the French Broad River in Asheville, North Carolina, marking the first such sighting in that part of the state.[23]
Non-migratory trumpeter swans have also been artificially
introduced to some areas of Oregon, where they never originally
occurred. Because of their natural beauty, they are suitable water fowl
to attract bird watchers and other wildlife enthusiasts. Introductions
of non-indigenous species in the Western states, for example through the
Oregon Trumpeter Swan Program (OTSP), have also been met with
criticism, but the introduction program argues that the perceived
attractiveness of natural sites has priority over the original range of
any given species.[24]
Occasional sightings of trumpeter swans have occurred in the United Kingdom;[25]
while some of these are believed to be vagrants, most are presumed
escapes into the wild. A single instance of the species breeding in the
United Kingdom is reported from 1997, where two swans out of a group
that escaped from a wildfowl collection at Apethorpe Palace, Northamptonshire raised a single cygnet on the River Nene.[26]
Diet
In winter, they may eat crop remnants in agricultural fields, but more commonly they feed while swimming
These birds feed while swimming, sometimes up-ending or dabbling to
reach submerged food. The diet is almost entirely aquatic plants. They
will eat both the leaves and stems of submerged and emergent vegetation.
They will also dig into muddy substrate underwater to extract roots and
tubers. In winter, they may also eat grasses and grains in fields. They
will often feed at night as well as by day. Feeding activity, and the
birds' weights, often peaks in the spring as they prepare for the
breeding season.[27] The young initially include insects, small fish, fish eggs and small crustaceans in their diet, providing additional protein, and change to a vegetation-based diet over the first few months.
Breeding
Like other swans, trumpeter swans often mate for life,
and both parents participate in raising their young, but primarily the
female incubates the eggs. Most pair bonds are formed when swans are 5
to 7 years old, although some pairs do not form until they are nearly 20
years old. "Divorces" have been known between birds, in which case the
mates will be serially monogamous, with mates in differing breeding
seasons. Occasionally, if his mate dies, a male trumpeter swan may not
pair again for the rest of his life.[18]
Most egg laying occurs between late April and May. The female lays 3–12
eggs, with 4 to 6 being average, in a mound of plant material on a
small island, a beaver or muskrat
lodge, or a floating platform on a clump of emergent vegetation. The
same location may be used for several years and both members of the pair
help build the nest.[18]
The nest consists of a large, open bowl of grasses, sedges and various
aquatic vegetation and have ranged in diameter from 1.2 to 3.6 m (3.9 to
11.8 ft), the latter after repeated uses.[28] The eggs average 73 millimetres (2.9 in) wide, 113.5 millimetres (4.5 in) long, and weigh about 320 grams (11.3 oz).[18]
The eggs are quite possibly the largest of any flying bird alive today,
in comparison they are about 20% larger in dimensions and mass than
those of an Andean condor (Vultur gryphus), which attains similar average adult weights, and more than twice as heavy as those of kori bustards (Ardeotis kori).[29][30][31]
The incubation period is 32 to 37 days, handled mainly by the female,
although occasionally by the male as well. The young are able to swim
within two days and usually are capable of feeding themselves after, at
most, two weeks. The fledging stage is reached at roughly 3 to 4 months.[32] While nesting, trumpeter swans are territorial and harass other animals, including conspecifics, who enter the area of their nest.[18]
Though the range of the two species does not overlap, the trumpeter swan can hybridise with its close relative, the whooper swan,
and hybrid birds have been observed in the wild, most likely as a
result of interbreeding between wild trumpeter and vagrant or introduced
whooper swans.[33][34]
Adults go through a summer moult
when they temporarily lose their flight feathers. The females become
flightless shortly after the young hatch; the males go through this
process about a month later when the females have completed their moult.
Mortality
In
captivity, members of this species have survived to 33 years old and, in
the wild, have lived to at least 24 years. Young trumpeter swans may
have as little as 40% chance of survival due variously to disturbance
and destruction by humans, predation, nest flooding, and starvation. In
some areas, though, the breeding success rate is considerably greater
and, occasionally, all cygnets may reach maturity. Mortality in adults
is quite low, with the survival rate usually being 80–100% annually,
unless they are hunted by humans.[35] Predators of trumpeter swan eggs include common ravens (Corvus corax), common raccoons (Procyon lotor), wolverines (Gulo gulo), American black bears (Ursus americanus), grizzly bears (Ursus arctos horribilis), coyotes (Canis latrans), gray wolves (Canis lupus), mountain lions (Puma concolor), and North American river otters (Lontra canadensis).[36][37][38][39][40][41][42]
Nest location can provide partial protection from most mammalian nest
predators, especially if placed on islands or floating vegetation in
deep waters. Most of the same predators will prey on young cygnets, as
will common snapping turtles (Chelhydra serpentina), California gulls (Larus californicus), great horned owls (Bubo virginianus), red foxes (Vulpes vulpes) and American mink (Neogale vison).[37][39][43][44][45][46] Larger cygnets and, rarely, nesting adults may be ambushed by golden eagles (Aquila chrysaetos), bobcats (Lynx rufus), and probably both coyotes and gray wolves.[44][46][47]
When their eggs and young are threatened, the parents can be quite
aggressive, initially displaying with head bobbing and hissing. If this
is not sufficient, the adults will physically combat the predator,
battering with their powerful wings and biting with their large bills;
adults have managed to kill predators equal to their own weight in
confrontations.[48][49] Predation of adults when they are not nesting is rare; they may possibly be hunted by golden and bald eagles, but substantiated cases are few. Photos of an exceptional attack by a bald eagle (Haliaeetus leucocephalus) on adult trumpeter swan in flight were taken in 2008, although the swan survived the predation attempt.[50]
Conservation status
Adult and three juvenile trumpeter swans on the shore of Woods Lake, near Oyama, British Columbia
Near extinction and rediscovery in Alaska
In
the 19th and early 20th centuries, the trumpeter swan was hunted
heavily, for game or meat, for the soft swanskins used in powder puffs,
and for their quills and feathers. This species is also unusually
sensitive to lead poisoning from ingesting discarded lead shot from fishing weights while young. The Hudson's Bay Company captured thousands of swans annually with a total of 17,671 swans killed between 1853 and 1877. In 1908 Edward Preble wrote of the decline in the hunt with the number sold annually dropping from 1,312 in 1854 to 122 in 1877.[51] Sir John Richardson
wrote in 1831 that the trumpeter "is the most common Swan in the
interior of the fur-counties... It is to the trumpeter that the bulk of
the Swan-skins imported by the Hudson's Bay Company belong."[52]
By the early twentieth century breeding trumpeter swans were nearly
extirpated in the United States, with a remnant population of fewer than
70 wild trumpeters in remote hot springs in or near Yellowstone National Park. Surprising news came from a 1950s aerial survey of Alaska's Copper River when several thousand trumpeters were discovered.[4]
This population provided critical genetic stock to complement the
tri-state (Montana/Idaho/Wyoming) population for re-introductions in
other parts of the swan's historic range.
Historical range
In 1918 Joseph Grinnell wrote that trumpeter swans once bred in North America from northwestern Indiana west to Oregon in the U.S., and in Canada from James Bay to the Yukon, and they migrated as far south as Texas and southern California.[20] In 1960 Winston E. Banko also placed their breeding range as far south as Nebraska, Missouri, Illinois, northwestern Indiana, but in Michigan turned this line northwards, placing a hypothetical eastern boundary up through Ontario to western Quebec and the eastern shore of James Bay.[39]
In 1984, Harry G. Lumsden posited that trumpeter swans may have been
extirpated from eastern Canada by native people armed with firearms
prior to the arrival of European explorers and noted archaeological
remains of trumpeter swans as far east as Port au Choix, Newfoundland dating to 2,000 BCE. He cited historical observer records of what must have been breeding trumpeters, such as Father Hennepin's August report of swans on the Detroit River from Lake St. Clair to Lake Erie in 1679 and Antoine de la Mothe Cadillac's
1701 report of summering swans (July 23 – October 8) in the same area:
"There are such large numbers of swans that the rushes among which they
are massed might be taken for lilies."[53] In the eastern United States the breeding range is potentially extended to North Carolina
by the detailed report of John Lawson (1701) that "Of the swans we have
two sorts, the one we call Trompeters...These are the largest sort we
have...when spring comes on they go the Lakes to breed" versus "The sort
of Swans called Hoopers; are the least."[54]
Reintroduction
Early
efforts to reintroduce this bird into other parts of its original
range, and to introduce it elsewhere, have had modest success, as
suitable habitats have dwindled and the released birds do not undertake
migrations. More recently, the population in all three major population
regions have shown sustained growth over the past thirty-year period.
Data from the US Fish and Wildlife Service[55] show 400% growth in that period, with signs of increasing growth rates over time.
One impediment to the growth of the trumpeter swan population around the Great Lakes is the presence of a growing non-native Eurasian mute swan population who compete for habitat.[7][56]
Alberta
One of the largest conservation sites for the trumpeter swan is located in Lois Hole Provincial Park. It is located adjacent to the renamed Trumpeter subdivision of Edmonton, Alberta, within Big Lake.
Michigan
Joe Johnson, a biologist for the W.K. Kellogg Bird Sanctuary, part of Michigan State University’s Kellogg Biological Station,
obtained trumpeter swans from Alaska for re-introduction to Michigan
beginning in 1986. The population has grown via continued
re-introductions and organic growth to 756 birds by 2015. The native
swans have benefited from removal of non-native mute swans by the Michigan Department of Natural Resources beginning in the 1960s, with a decline from 15,000 mute swans in 2010 to 8,700 in 2015.[57]
Minnesota
As of 2013, the trumpeter swan is no longer listed as threatened in the state of Minnesota.[58] In the winter months, a large population of trumpeter swans can be seen in the city of Monticello, Minnesota. [59]
Ontario
The
Ontario Trumpeter Swan Restoration Group started a conservation project
in 1982, using eggs collected in the wild. Live birds have also been
taken from the wild. Since then, 584 birds have been released in
Ontario. Despite lead poisoning in the wild from shotgun pellets, the
prospects for restoration are considered optimistic.[60]
Yellowstone National Park
As
of 2018, only two pairs of swans allegedly remained in the park. They
have not bred in years. Scientists attribute the loss in the park's
population to the loss of nests and nesting sites because of spring
flooding caused by climate change. [61]
Mating Behaviour
Courtship and Mate choice Behaviours
In
late April, breeding pairs meet to begin the 11 to 35 day process of
constructing a nest. Before this grueling process can come to be, much
like many other species of birds, these creatures undergo several courtship rituals.[62]
Trumpeter Swans have a strong tendency to avoid interactions with
conspecifics, therefore it is implied that at first contact of a
potential mating pair there is some unwillingness in the male and female to make this connection.[63]
In order to overcome the initial encounter there are two common
displays that can occur. At first, the male tends to pursue the female
in a non aggressive way. When the female allows the approach the male
will touch the breast of its body to the flank of the female which then
causes both individuals the touch the beasts of their bodies together.[63]
At this point the feathers on the neck of the make is stood up and the
bills of the mating pair are pointed down indicating pacification.
Another act of courtship occurs when a male swims in the direction of a
possible mate and continuously turns its head from side to side to get
the attention or perhaps impress the female.[63]
Other common behavioural displays presented by the pair include
spreading and raising their wings, the rapid or almost quivering motion
of the wings, particular head motions that include bobbing, and finally
the most known (and what the name of this animal originates) is the
trumpeting that occurs.[64]
Acoustic communication among Trumpeter Swans is incredibly common among
all ages of the species. From the young cygnets to the adult swans,
their calls are incredibly distinct and have a wide variety of functions
in the survival of the animal. The classic Trumpet call can be heard
from long distances and is the most common communication mechanism heard
among these birds. This type of call resembles a horn because the
frequency can vary greatly. This call generally occurs when an animal is
alarmed or feels threatened, the call acts as a warning or even a way
in deterring incoming predators due to the abrupt volume of the noise
being evoked.[64]
More specifically referring to mating, the call that is most common
among mating pairs is called the duet. This call happens when a pair has
come together near breeding season. The duetting process can begin as
separate trumpeting solos and can evolve into an almost simultaneous
duet that is very similar in frequency and very difficult to tell the
individual calls apart.[65]
This performance of the pair is commonly associated with the particular
movements mentioned above (head bobbing and wing movements) associated
with the courtship. Also, the duet can aid in coordination of a duel
attack on a predator that is too close to the nest of a mated pair.[65] In terms of mate choice,
the Trumpeter swan continuously returns to the mate from previous
breeding terms, often the breeding pair will even return to their
previous breeding grounds if previous offspring were successful in that
area.[66]
Nesting and Incubation Behaviour
The fabrication of a nest
is an incredibly precise process that takes place over a series of 11
to 35 days and typically breeding pairs will begin construction in late
April.[67]
The time of year the nest-building process begins can slightly vary due
to weather conditions in the previous year, if the environment was more
cold and wet the females may not be heathy enough to being mating right
away and as a result the nesting behaviour might be slightly delayed.
It is common to find nests of trumpeter swans surrounded by water or
close to water. This is advantageous to the parents because it can
reduce the risk of predation, it can provide optimal foraging sources such as aquatic vegetation as well as ensuring there is nearby water for when the cygnets are hatched.[67]
The long duration of the nest building process is predominantly due to
the nest being so large (1.2 to 3.6m in diameter) and fabricated mainly
from submerged vegetation as well as grasses and grass-like plants.[67]
The nest is mostly constructed by the male while the female of the
breeding pair is focused on feeding and preparing for the arrival of the
cygnets. It has been observed that adult Trumpeter swans do not
directly bring the building materials directly to the nest building
site. The males use a specific action that includes facing away from the
nest and throwing organic materials over their shoulder moving closer
and closer to the nesting area[68].Eventually
when they arrive at the nesting site the two individuals of the mating
pair are involved in the construction, but, as mentioned above the male
spends the majority of its time doing the construction. During nest
construction, female Trumpeter swans feed significantly more frequently
than males in order to fuel up for laying the eggs.[69]
This is greatly supported by the male counterpart of the species
because ultimately if the female is keeping itself healthy it will in
the end ensure healthy offspring which improves the fitness of the mating pair. Typically a female Trumpeter swan will lay four to six eggs and will incubate them for 32 to 37 days until they hatch.[70]
After the eggs are laid it is the female that spends the majority of
the time incubating, it has been observed that around every 20 minutes
the female will stand up from incubating and reach down beneath itself
to roll over the eggs with its bill before re assuming the incubation
position.[71]
It can be inferred that this behaviour is used to ensure the eggs are
kept an appropriate temperature on all sides, this is very important
because exposure to the elements leads to high mortality
rates in cygnets. The female only leaves the incubation process for
brief recesses that last around 20 minutes. Before the female leaves for
the recess it will cover the eggs with plant material and it has been
observed that if the females does not cover the eggs the male will do so
in the absence of the female.[72]
This time away from the nest is primarily used for feeding, but the
female has also been observed using this time for bathing and preening.[73] The only other time the female leaves the nest is when it must help the male chase away predators from their nesting territory.[74]
It is highly uncommon for both members of a mating pair to be absent
from the nest at the same time, there is generally always a male or a
female present guarding the eggs.[75]
The behavior of the male during and after the laying of the eggs can be
best described as on alert. This is due to males being increasingly
territorial and aggressive, particularly when a predator or conspecifics
approach the nesting area.[74]
Generally when females leave the nest during their brief recesses the
males will stand and guard the eggs, although in some cases the males
would even sit on the eggs in the absence of a female swan.[75]
Parental Behaviour
In
the Trumpeter Swan there is a very clear division of labor between male
and female parts of a breeding pair. This division is referring to
clear roles that each parent knows to accomplish in the process leading
up to, during, and after the mating process.
Males
After the
meeting of the pair prior to mating or nest building the male will often
initiate courting calls which results in the duet mentioned above.
Before and throughout the laying period the male can be found dealing
with construction of the nest and collection of resources. As the eggs
are being incubated by the female the male does not feed or sleep as
often particularly when the female left the nest. These trends also were
associated with more aggressive behaviors from the male especially
towards predators and other members of the species.[76] When it comes to parental behaviour,
the male has already completed the majority of its role. With this in
mind, the male does continue to be territorial and protective of the
newly developing cygnets as well as allowing the female to replenish its
nutrient reserves. This makes migration to wintering grounds possible and allows for more years of breeding.[76]
Keeping the female of the mating pair healthy is important for
Trumpeter swans because this species tends to only have one mate in its
lifetime. A healthy female also improves the likelihood of having more
successful clutches are well as better nesting experiences.[76] When cygnets are young it is common to see the male accompanying them in feeding recesses outside the nest.[77] This can fall under the category of the main male role in parenting being the protection of the offspring.
Females
The
increased care and attention of the male to the young allowed for the
female to feed more frequently and exert more energy toward protection
and overall health to the developing cygnets.[78]
During the pre-laying/laying period the males are significantly more
active than the females of the breeding pair. This is advantageous in
because it aids in the fitness of the species by improving reproductive
success by allowing the female, as mentioned above, to feed more
frequently and overall replenish the energy stored in order to aid in
incubation and other crucial activities.[78]
When hatching occurs the females tend to not leave the nest, the only
time a female may leave would be to chase away a nearby predator.[79]
After hatching the cygnets are brooded for the first one to two days by
the female, cygnets are also brooded when needed (when it is cold or at
night) for the first few weeks of their lives.[80]
Young offspring have a very close relationship with their parents in
the first part of their lives spending the majority of their first few
weeks with the female in the nest or in the water.[79] Offspring tend to spend their first full winter with their parents and then they no longer need them.[80]
See also
Binomial name
Cygnus buccinator
Geographical distribution of Trumpeter swan.
Breeding
Year-round
Nonbreeding
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_Summer_Range_of_Trumpeter_Swan_USFWS.png)
