Status and movements of reintroduced Trumpeter Swans Cygnus buccinator, and the status and control measures for non-native Mute Swans Cygnus olor, in Ohio, USA

Abstract

A programme to reintroduce the native Trumpeter Swan Cygnus buccinator to Ohio commenced in 1996, after the species had been extirpated from the state for nearly three hundred years. Reintroduction releases continued through to 2003, when the population reached the management goals of the state’s wildlife agency, the Ohio Department of Natural Resources – Division of Wildlife. Trumpeter Swan population growth was initially slow but began to increase more rapidly, likely because of management actions such as the continued protection and restoration of wetlands, control of invasive plant and animal species, and continued state legal protection of the swans. From 2003 to the 2023 breeding season, the number of breeding Trumpeter Swan pairs continued to grow at an average annual rate of 15.5% (s.d. ± 26.3%), and successful breeding pairs averaged 2.22 ± 0.40 cygnets per year. In recent years, large flocks of non-breeding Trumpeter Swans (50–200 individuals, which may include some failed breeders) have been seen in summer at sites across the state. Monitoring and management of swans in Ohio has also included counts of and control measures for non-native Mute Swans Cygnus olor since 2006 with the latter causing a decline in Mute Swan numbers in recent years, which may have contributed to improved Trumpeter Swan breeding success. Whether Trumpeter Swans breeding in Ohio migrate during the non-breeding season, however, remained unknown. In 2020 and 2021, twenty adult Trumpeter Swans therefore were captured and tagged with GPS/GSM transmitters fitted to neck collars, to determine whether they were migratory or sedentary. The tracking data showed that most dispersed locally (remaining < 40 km from their capture site) between July 2020 and July 2022, but three undertook long-distance movements. One hypothesis to explain these short movement patterns is that, because swans in Ohio are at the southern periphery of their current breeding distribution and experience mild winter conditions, they do not need to migrate to have open water and food available throughout the winter. Overall, the Trumpeter Swan reintroduction programme in Ohio has been successful but, as the population is primarily non-migratory, it continues to remain a year-round management responsibility of the Ohio Department of Natural Resources – Division of Wildlife.