Reproductive Success of Exotic Mute Swans in Connecticut

Abstract

Mute Swans (Cygnus olor) are native to Eurasia and were introduced to North America, where free-ranging populations have existed since the early 1900s (Allin et al. 1987). Originally observed in New York, breeding populations of Mute Swans have expanded into all of the Atlantic coastal states from Maine to Maryland and also have become established in Michigan, Minnesota, Wisconsin, British Columbia, and Ontario (Willey and Halla 1972; Reese 1975, 1980; Allin et al. 1987; Knapton 1993). Allin et al. (1987) synthesized 33 years of population data on Mute Swans from the Atlantic Flyway and estimated a 1987 population of 5,300, with most of the birds in New York, Connecticut, Rhode Island, and New Jersey. In the southern New England states of Massachusetts, Rhode Island, and Connecticut, Mute Swans constitute a single population with considerable interchange of individuals among states (Willey and Halla 1972). During the 1960s and 1970s, the Chesapeake Bay population nested mostly on estuaries and tidal rivers (Reese 1975, 1980), as did the southern New England population (Willey and Halla 1972, Kania and Smith 1986). For instance, 90% of the Mute Swans in Rhode Island in 1967 nested on estuaries, and no nests were more than 5 km inland (Willey and Halla 1972). Since then, large numbers of Mute Swans in southern New England have started breeding at inland sites on lakes and ponds. Expanding Mute Swan populations may have detrimental effects on native biota. One concern is the influence of swan herbivory on aquatic vegetation (Willey and Halla 1972, Reese 1975, Allin et al. 1987, Conover and Kania 1994) and associated macro-invertebrates (Krull 1970); another is that Mute Swans are aggressive toward other waterfowl species (Willey and Halla 1972, Kania and Smith 1986, Allin et al. 1987, Conover and Kania 1994). Because many native species of waterfowl nest at inland sites, Mute Swans may pose more of a threat to native avifauna at inland sites than at estuaries and tidal rivers (Wil-