Mute swan (Cygnus olor)

Synonyms: Anas olor, Sthenelides olor

Common Names: White swan, tame swan, Polish swan

Description:

The mute swan (Cygnus olor) is a large, all-white waterbird brought to North America from Europe and Asia in the late 1800s as an ornamental bird for parks and estates [1]. Some escaped or were released, and the species now lives wild on lakes, ponds, and coastal bays across much of the country [1]. MISIN tracks it because it eats huge amounts of underwater plants, drives off native birds, and can be dangerous to people who get too close [1][3].

Identification:

The mute swan is one of the largest birds you will see on the water. Adults are pure white and very big ? the body can be about 5 feet long, the wingspan stretches more than 7 feet, and a heavy bird can weigh 20 to 31 pounds [2]. The easiest way to tell it apart from a native swan is the bill: it is bright orange with a black fleshy knob at the base, sitting above a small black face patch [2]. Mute swans usually hold their long neck in a graceful S-curve with the bill tilted down, while native swans hold the neck straight up [2].

You can see mute swans year-round in many areas, but they are most noticeable ? and most aggressive ? in spring and early summer (about March through July), when pairs are nesting and raising young [3]. The gray-brown young, called cygnets, follow the adults on the water through the summer [2].

At-a-glance cues:

1. Very large all-white bird; body up to about 5 feet long with a wingspan over 7 feet [2]
2. Bright orange bill with a black knob at the base, above a black face patch [2]
3. Long neck usually held in a graceful S-curve, bill pointed down [2]
4. Gray-brown young (cygnets) with a dark or pinkish bill, seen in summer [2]

Habitat:

Mute swans live on calm fresh and brackish (slightly salty) water ? lakes, ponds, slow rivers, marshes, and coastal bays and estuaries [1]. They are native to Europe and Asia. In North America they are now established across much of the eastern United States, the Great Lakes region, and parts of the Pacific Northwest [1].

They feed mostly on submerged plants, pulling up the leaves, stems, and roots from the bottom. A single adult eats about 3 to 4 kilograms (roughly 8 pounds) of wet plant material every day, and tears up even more than it swallows [1]. During the nesting season a pair defends a large territory ? as much as 15 acres of wetland ? and chases off other birds that come near [1].

Reproduction:

Mute swans reach new water bodies mostly by flying in on their own from nearby populations. They also turn up after escaping or being released from private ponds and ornamental collections [1][3]. So a pair can simply land on a neighborhood pond and decide to stay.

Pairs often stay together for years and return to the same area to breed. In spring they build a large mound nest out of plants at the water's edge. The female lays about 5 to 9 eggs (sometimes as many as 10) and sits on them for roughly 36 days before they hatch [2]. A healthy pair can raise a brood every year and live 20 years or more, so a few birds can grow into a large local flock in just a few seasons where nothing keeps them in check [1][3]. Because of this, wildlife managers time control work ? such as treating eggs in the nest ? to the spring incubation period, before the eggs hatch [3].

Impact and Damage:

Mute swans can be dangerous to people. They are very territorial in spring and summer, and a defending bird will hiss, charge, and strike with its wings and bill [3]. With a wingspan over 6 feet, a swan can knock a person down and cause bruises, sprains, and even broken bones [3]. Attacks on small children and on people in kayaks, canoes, and small boats are reported regularly; in one Chicago case a swan capsized a man's kayak and he drowned [3]. Keep children and pets well back from these birds, especially near a nest.

The bird is also hard on the water itself. Eating 3 to 4 kilograms of underwater plants a day and uprooting more, large flocks strip the beds of submerged plants that fish and native birds depend on [1]. In a Chesapeake Bay study, areas grazed by mute swans had 79% less plant cover, 76% fewer plant shoots, and a plant canopy 40% shorter than fenced-off areas the swans could not reach. Losing these underwater plants harms fish nurseries, water quality, and food supplies for native waterfowl. On top of that, mute swans aggressively drive native ducks, geese, and native swans off their nesting and feeding areas [1][3].

Similar species:

Two native swans are the main look-alikes. The trumpeter swan and the tundra swan are both all white like the mute swan, but each has an all-black bill with no orange and no knob, and both hold the neck straight and upright rather than in a curve [1][2]. The tundra swan is a bit smaller and often shows a small yellow spot near the eye [2]. Domestic white geese and the snow goose are sometimes confused with young swans, but geese are much smaller and shorter-necked, and the snow goose shows black wingtips in flight [2].

Monitoring and rapid response:

Signs to watch for:

1. Large all-white swans with an orange, black-knobbed bill on ponds, lakes, rivers, or coastal bays [2]
2. Swans hissing, charging, or striking at people or other birds near the water in spring and early summer [3]
3. A large mound nest of plant material at the water's edge, defended by a pair [3]

What you can do:

The mute swan is a wild bird, so removing a swan, nest, or eggs is regulated and is not a do-it-yourself task. Unlike native swans, the mute swan is not protected under the federal Migratory Bird Treaty Act [4], but you should always check with your local wildlife agency before taking any action against a swan, its nest, or its eggs [3]. On your own property you can safely:

1. Keep your distance, especially from March through July near a nest, and keep children and pets back; stay out of the water near an aggressive swan [3].
2. Stop feeding swans and other waterfowl, and take bird feeders down for two to three weeks, since easy food keeps swans in the area [3].
3. Make the shoreline less inviting by letting tall plants, shrubs, or rocks grow along the water's edge to block the bird's path between water and land [3].
4. Report what you see (below) so agencies can track and respond to new birds.

Natural area crews can monitor a whole waterbody, focus on removing small, newly arrived populations and lone pairs before they take hold, and work with wildlife agencies on permitted egg treatment or removal [3].

When to call a professional:

1. Established or growing flocks, or birds that aggressively threaten people.
2. Any removal of swans, nests, or eggs ? this needs trained wildlife professionals and agency authorization [3].
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. IUCN Global Invasive Species Database. Cygnus olor (Gmelin, 1789). iucngisd.org
2. Cornell Lab of Ornithology. Mute Swan (Cygnus olor) ? Identification & Life History. All About Birds. allaboutbirds.org/guide/Mute_Swan
3. USDA APHIS Wildlife Services. Mute Swans (Wildlife Damage Management Technical Series). aphis.usda.gov
4. U.S. Fish & Wildlife Service (2005). Final List of Bird Species to Which the Migratory Bird Treaty Act Does Not Apply. Federal Register, March 15, 2005. federalregister.gov

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