Mute swans are large, white waterfowl that are native to Europe and Asia but have also become established in North America. Determining the exact number of mute swans currently residing in the United States is challenging, but estimates can be made based on population surveys and reports. In this article, we will explore what is known about the number of mute swans in the US and the methods used to estimate populations.
Background on Mute Swans
The mute swan (Cygnus olor) is native to mainland areas of Europe and Asia, but has been introduced as an ornamental species in other parts of the world including North America. They were brought from Europe to the United States in the late 1800s to decorate parks, zoos and estates. After escaping or being intentionally released, feral populations became established along the Atlantic coast and in other areas of the country.
Mute swans are large birds, with males averaging 10-15 lbs and females 8-12 lbs. Their wingspan is up to 10 feet wide. As their name suggests, mute swans are much quieter than other swans and lack the black knob on the base of the bill that makes the trumpeting call in other swan species. However, mute swans do make grunting, snorting and hissing vocalizations.
Mute swans feed primarily on submerged aquatic vegetation which they access by plunging their long necks into the water. They will also graze on land. Their large size and territorial behavior enables them to outcompete many native waterfowl for food resources.
Populations in the Great Lakes Region
One region of the United States with a large number of mute swans is the Great Lakes. It is estimated that as of 2018 there were around 16,000 mute swans living in the Great Lakes Basin, with the majority located in Michigan.
The population in Michigan is concentrated primarily in the lower peninsula, with an estimated 13,500 swans as of 2010. Ohio had an estimated mute swan population of about 2,500 around the same time period.
Wisconsin and Minnesota had lower numbers of mute swans, with each state having several hundred birds. New York’s population within the Great Lakes region was approximately 500 as of 2010.
Overall, the combined mute swan population in the states bordering the Great Lakes was pegged at roughly 15,000 to 20,000 in the early 2010s. The population had grown substantially since the 1960s when there were only a few hundred swans in the entire Great Lakes region.
Great Lakes Population Changes
More recently, wildlife agencies have ramped up mute swan control efforts in the Great Lakes states which has stabilized or reduced the population to some degree. For example, Michigan’s mute swan population decreased from over 15,000 in 2001 to around 13,500 in 2010.
Ohio’s population has declined more significantly, dropping from around 4,500 in the mid 2000s to 2,500 by 2010, largely through addling (egg oiling) efforts. The summer 2015 population surveys for Lake Erie coastal marshes found only 164 mute swans, compared to over 700 birds in 2003.
Control measures in Wisconsin also reduced that state’s population from approximately 2,000 birds in 1987 down to 500 by 2010.
While total numbers have declined in recent years, mute swan populations remain substantial in many Great Lakes wetlands and management efforts are ongoing. The latest regional estimate is approximately 16,000 birds as of 2018.
East Coast Population
In addition to the Great Lakes, the Atlantic Coast of the United States has a significant mute swan population. It is centered primarily around the Chesapeake Bay region and coastal areas of Maryland and Virginia.
The Chesapeake Bay population was estimated at around 4,000 to 5,000 in the early 2000s but declined to 3,700 by 2010 after management actions were implemented. More recently the Chesapeake Bay mute swan population is thought to be approximately 3,000 birds.
Along the entire Atlantic coast and eastern seaboard, the mute swan population is roughly 10,000 to 15,000 birds according to Audubon estimates from the mid 2010s.
East Coast Population Changes
The East Coast mute swan population grew substantially in the late 1900s, increasing by about 10% annually from the 1960s through the 1990s. This rapid growth leveled off around the year 2000.
In Maryland, the population peaked at around 4,000 to 5,000 in 1999 before declining to 3,700 by the 2010 statewide count. The implementation of mute swan management plans has stabilized the population in Maryland and other Atlantic coastal states.
While still substantial, the Atlantic mute swan population appears to have leveled off compared to its rapid expansion in prior decades. Continued population management efforts along the East Coast will determine future trends.
Other U.S. Populations
In addition to the Great Lakes states and Atlantic Coast, mute swans have established smaller populations across many other areas of the United States, though not to the same extent. A few of the largest populations include:
- Pacific Coast: Approximately 700 mute swans as of the 2010s.
- Southeast U.S.: Several hundred in Louisiana, Georgia and South Carolina.
- Midwest: Scattered populations in states like Illinois, Iowa, Missouri, totaling a few hundred birds.
Isolated feral populations of varying sizes have also become established in many other states across the country from escaped or released captive mute swans.
National Population Estimate
When tallying up the known mute swan populations across different regions of the United States, a rough national estimate emerges:
- Great Lakes: 16,000
- Atlantic Coast: 10,000 – 15,000
- Other regions: 2,000 – 3,000
This puts the total US mute swan population in the range of approximately 30,000 birds as of the mid 2010s, according to the Atlantic Flyway Mute Swan Management Plan and other sources.
However, the exact number is difficult to pin down given the variable populations between regions and across years. The population could fluctuate from approximately 25,000 to as many as 35,000 mute swans nationwide.
While substantial, this represents a stabilization in recent years following populations that may have exceeded 40,000 birds in the early 2000s prior to management efforts.
Population Survey Methods
State and federal agencies use a variety of methods to survey and estimate mute swan populations across different regions of the country:
Breeding Bird Surveys
The USGS Breeding Bird Survey utilizes roadside counts of birds on established survey routes to estimate breeding populations and trends for hundreds of species nationwide. Mute swan numbers observed during these summer surveys provide data to estimate populations and growth.
Aerial Surveys
Some states conduct aerial surveys by plane or helicopter over wetland areas to visually count mute swan flocks. This allows large areas to be surveyed efficiently. For example, Michigan utilized aerial surveys to cover major wetland complexes across the state to derive population estimates.
Ground Counts
Many states and local agencies perform ground-based mute swan counts during breeding season when flocks congregate and are most visible. Counts may be done by vehicle along shorelines or by foot to access wetlands. Some counts are done by volunteers to help cover large areas.
Marking and Banding
Banding mute swans with neck collars and unique ID markers provides valuable data on populations and movement. The re-sighting rate of marked birds can help determine total populations. Banding also indicates population interchange between states.
Nest Surveys
Monitoring nesting sites located through breeding ground surveys gives an indication of reproductive rates and growth potential. Nest counts are combined with brood counts to estimate productivity.
By utilizing a combination of different survey methods, state and federal wildlife agencies are able to derive population estimates and monitor trends for mute swan flocks across the country.
Management and Control Efforts
Mute swans are considered an invasive species in North America, and can negatively impact native wetland ecosystems and wildlife. As a result, many states have implemented mute swan management plans to control populations.
Common control techniques include:
- Egg addling or oiling to reduce nest productivity.
- Removal and euthanasia of adult birds.
- Controlled hunting seasons allowing mute swan harvest in some states.
These management efforts have slowed the growth or reduced the size of certain mute swan populations, particularly in the Great Lakes and Chesapeake Bay.
While still considered invasive, it is unlikely mute swans will ever be fully eradicated from the United States given their well-established populations. Continued management will be needed to control numbers and impacts to ecosystems.
Potential Limitations of Population Data
When assessing the accuracy of mute swan population estimates in the United States, some potential limitations exist:
- Counts may miss some isolated swan flocks in remote wetlands.
- Aerial surveys only provide a snapshot and may not detect swans in wooded wetlands.
- Breeding bird survey routes may inadequately sample certain habitat types.
- Migration and movements between states can complicate estimates.
- Counts are inconsistent between years and surveying agencies.
Despite these caveats, the combination of different survey methods and data from multiple agencies likely provides a reasonable approximation of the total mute swan population size and distribution in the U.S. But the limitations highlight the difficulty of deriving a precise nationwide figure.
Population Data Summary by State
Here is a summary of the latest mute swan population estimates for some of the key states mentioned in this article:
State | Estimated Mute Swan Population |
---|---|
Michigan | 13,500 |
Maryland | 3,000 |
New York | 500 |
Wisconsin | 500 |
Ohio | 2,500 |
Minnesota | 400 |
This table summarizes the latest population totals for some of the states with the highest number of mute swans based on surveys conducted by state wildlife agencies during the 2000s and early 2010s.
Conclusion
In conclusion, the current total mute swan population in the United States is likely between 25,000 to 35,000 birds, based on data synthesized from multiple surveying agencies.
The Great Lakes region contains the highest number at approximately 16,000, while the Atlantic Coast population is estimated to be 10,000-15,000. Smaller populations in the Pacific Coast, Southeast, Midwest and other areas comprise the remainder.
While still considered an invasive species, mute swan numbers have stabilized in recent years due to management efforts to control populations through egg addling, removals, and hunting. Continued surveys and counts will monitor future trends in this introduced but now well-established waterfowl species.
Precisely tallying mute swans across the varied regions and wetlands of the entire country is difficult. But current survey methods and coordinated data allow reasonable estimates of the total U.S. population size and distribution.
Improving survey accuracy through new techniques and increased monitoring will help track mute swan numbers into the future.