Controlling Mute Swans (Cygnus olor) in Ohio
Mute swans are native to Eurasia and were introduced into North America during the late 1800s as decorative waterfowl. They have now established wild populations in all 4 flyways from escaped and released birds. Mute swans were first seen in Ohio in 1911 at Silver Lake, Akron where they were wing-clipped annually until 1934 when the birds were allowed to fly away. The first published record of non-captive mute swans occurred during the winter of 1936, but they did not regularly winter in Ohio until the 1960s. By 1987, mute swans were nesting at Ottawa National Wildlife Refuge, Buckeye Lake, and Senecaville Lake.
The U.S. Fish and Wildlife Service has traditionally excluded non-native species from the list of migratory birds (50 CFR 10.13) which are protected by the Migratory Bird Treaty Act
(MBTA). However, in December 2001, the United States Court of Appeals for the District of Columbia Circuit ruled that mute swans are covered by the MBTA and all Anatidae
(the biological family incorporating ducks, geese, and swans) should be included in the list of migratory birds that are protected under federal 50 CFR regulations. The Migratory Bird Treaty Reform Act
(MBTRA) of 2004 invalidated that ruling and removed federal protection from all non-native avian species.
In Ohio, the mute swan was defined as a nongame species because it was not listed as a game species (Ohio Administrative Code 1501:31-1-02
[S-T]; Ohio Revised Code 1531.01
[S-T]). Wording in the 2006 omnibus bill changed the definition of migratory game birds to include mute swan (Ohio Revised Code 1531.01-AAA); however, the current Ohio Administrative Code definition of waterfowl (OAC 1501:31-1-02 [EEEEE]) needs to be clarified to make specific reference to swans as a member of the Family Anatidae
. This change is planned for Spring 2011 and will ensure consistency between definitions in both the Ohio Revised Code and the Ohio Administrative Code.
Biology and Management Concerns
Mute swans are sedentary birds that migrate short distances when dictated by weather severity. In addition, mute swans feed extensively on aquatic vegetation (up to 8 pounds per day), and in high densities they can overgraze an area. Intensive feeding activities from mute swans have a direct effect on plant diversity, fish assemblages, water quality/erosion control, and vegetation available to native waterfowl. Aggressive behavior towards other species, including humans, is another concern. Although the degree of antagonism varies among breeding pairs and within seasons, mute swans aggressively defend their nesting territories against other wildlife including Canada geese (Branta canadensis), ducks, waterbirds, and mammals. Mute swans may even kill the intruding birds and their young. People have also been subjected to the swans’ attacks while boating.
Competition between mute swans and the state-endangered trumpeter swan (C. buccinator) occurs frequently in the Lake Erie marshes. Mute swans establish territories (3-15 acres) and initiate nesting about 3 weeks earlier than trumpeter swans and successfully defend them from trumpeter swans. With only 105,000 acres of marsh existing in Ohio, competition for limited habitat has potential negative effects on the ODNR Division of Wildlife’s trumpeter swan restoration program. This is even more likely to occur as the mute swan population continues to increase. Petrie and Francis (2003) estimated the Great Lakes mute swan population had an annual growth rate of at least 10% which would cause the population to double every 7 or 8 years. Christmas Bird Counts conducted in Ohio have also indicated a general trend of increasing abundance as shown in the figure below.
Number of mute swans counted per observation hour on Christmas bird counts in Ohio, 1980-2009.
Control of Mute Swans
Following the lead of several other Midwestern states (e.g., Minnesota and Wisconsin), the Division will enact a mute swan action plan in an attempt to halt the increase of this exotic species. Implementation of mute swan management must occur concurrently with an effort to educate and inform Ohio citizen’s about mute swans. Authority for the Division of Wildlife to conduct a management program for migratory game birds, including mute swans, was established in August 2010 in Ohio Administrative Code 1501:31-7-06
(L) which states that “Provisions of this rule and rule 1501:31-7-02 shall not apply to employees of the division of wildlife or persons authorized by the chief of the division of wildlife while conducting activities as part of a management program for migratory game birds that has been approved by the chief of the division of wildlife.”¬ Educational components of such a program should convey an understanding of the status of the mute swan population in Ohio, the impact of mute swans on Ohio’s ecosystem and native wildlife, and the problems they create for people.
The mute swan action plan has 6 goals:
- Educate the public on the adverse consequences of mute swans on the environment
The Division’s Web site will be the primary means used to educate the public on the ecological impacts and conflicts caused by mute swans. The Division will also give technical advice and support to any agency/organization or private landowner to help control mute swans on lands they own or manage.
- Eliminate any mute swan conflicts which involve human safety
Health and human safety is a primary concern of the Division when handling wildlife conflicts. Any mute swans which threaten the well-being of people, or cause injury, will be removed. In addition, property owners who encounter mute swans that prevent people from utilizing their property may request the removal of the offending swans. Division staff will address such requests by providing technical assistance or removing the mute swans depending on site-specific circumstances.
- Reduce competition between mute swans and trumpeter swans
As noted above, mute swans may limit trumpeter swan use of wetland habitats for breeding. Trumpeter swans territory sizes (4 - 245 acres) are larger than those of mute swans (3 - 15 acres) so any mute swans on small to moderate-sized wetland areas may preclude use by trumpeter swans. Thus, mute swans on or near public lands which are used by trumpeter swans will be removed whenever possible. Likewise, efforts will be made to educate and work with landowners and local residents on private lands with similar circumstances to aid in removal of mute swans. Ohio’s trumpeter swan reintroduction program has been successful to date, but the species is still listed as endangered in Ohio; thus, removal of mute swans from areas used by trumpeter swans is necessary to ensure the long-term success of the program.
- Minimize detrimental impacts of mute swans on native wetland birds
As previously noted, mute swans often dominate within their own breeding territories and chase away all other birds and occasionally mammals. Where practical, the Division will implement its policy of minimizing impacts caused by exotic species by removing mute swans which limit breeding or habitat use by native fauna.
- Prohibit the release of mute swans into the wild
The release of any nonnative wildlife species or domestic animal into the wild can have negative consequences on habitat and native wildlife, including the spread of disease. In addition, allowing the release of mute swans while the Division is attempting to restore a native swan species is counterproductive. Ohio Wildlife Rehabilitators are already banned from rehabilitating and releasing mute swans. The possession of captive mute swans is already regulated by federal permit (50 CFR 21.25). State regulations should be developed to prevent people from releasing mute swans into the wild and to prohibit the sale, trade, barter, and importation of mute swans, or their eggs, in Ohio.
- Implement control measures to reduce mute swan numbers in Ohio
Policy 41 (Invasive Non-native Free-ranging Terrestrial Vertebrate Policy) already directs the Division to humanely dispatch mute swans, using the American Veterinary Medical Association’s 2007 Guidelines for Euthanasia, on Division-owned or managed properties. Methods to control mute swan populations should include egg addling, shooting (preferably head shots with shotguns and use of metro barrels and sub-sonic ammunition in urban/suburban areas), and live-capture/euthanasia.
The 2 most effective times to implement control measures are during nesting and molting season. During nesting season, mute swans can be easily approached because they are territorial and will readily defend their nest. Also, adult mute swans annually molt in late spring or early summer and are incapable of flight at that time, similar to Canada geese. During molting season, mute swans are extremely vulnerable and can be captured or shot from motorboats.
On non-Division public lands, Division staff should be proactive and encourage managers to control mute swan numbers. If staff resources are available, the Division may conduct the control work or provide technical assistance and the permits necessary to euthanize mute swans consistent with the goals of this action plan. On private properties with landowner permission, lethal control measures may be employed by Division staff when deemed feasible. Based on landowner-imposed restrictions or public sentiment, egg addling may be the sole method of control on private properties; under such circumstances, Division staff will provide technical advice on this procedure to landowners.