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Productivity and Fledging Success of Trumpeter Swans in Yellowstone National Park, 1987–2007

Abstract. Trumpeter Swan nesting in Yellowstone was monitored from 1987–2007 to assess the effects of environmental conditions, density-dependent factors and habitat characteristics on two metrics of productivity: clutch size and fledging success. Average clutch size was 4.2 eggs per nest (range = 3–6, SE = 0.2) and a positive relationship was found between clutch size and area of wetland complex surrounding the nesting site. The probability of fledging success (survival until September of at least one cygnet per nest) was associated with an increasing metric of territory quality (measured as historical site use from 1931–1986) and decreasing April precipitation. The probability of fledging success was estimated to range from 0.062 (95% CI = 0.060, 0.064) for a nest located in a wetland occupied only one time historically to 0.275 (95% CI = 0.073, 0.466) in a wetland occupied 38 times historically. The need to protect and maintain high quality nesting areas is underscored by the variability among nesting territories. The importance of adult survival is highlighted by the low productivity of Yellowstone Trumpeter Swans because pairs likely need to survive and nest many times to replace themselves.