Sizes and Long-Term Trends of Duck Broods in Maine, 1955–2007

Abstract

Productivity is a primary parameter used in waterfowl population models; however, few long-term metrics of reproductive output exist for eastern North American waterfowl. We used 52 years of brood survey data from throughout Maine to determine mean Class III brood sizes for Lophodytes cucullatus (Hooded Merganser), Anas platy- rhynchos (Mallard), Anas rubripes (American Black Duck), Aix sponsa (Wood Duck), Aythya collaris (Ring-necked Duck), and Bucephala clangula (Common Goldeneye). Us- ing model selection with theoretic-information approaches, we also investigated effects of wetland type, mean ambient temperature during nesting and brood rearing, and year (1955-2007) on trends in brood sizes. Brood sizes declined throughout the survey period for American Black Ducks (-0.88 ducklings/brood), Wood Ducks (-0.91), Ring-necked Ducks (-1.75), and Common Goldeneyes (-1.45). Declines in brood sizes in Maine are consistent with that of other metrics of productivity (e.g., age ratios of harvested water- fowl) for breeding ducks in Maine and may be cause for concern, especially given that declines in brood sizes were observed across a range of species with highly disparate life-history strategies. Declines in age ratios of hunter-harvested ducks could be indica- tive of range-wide declines in productivity resulting from decreased breeding propensity, nest success, clutch size, or duckling survival. Our fi ndings may suggest that declines in productivity observed in age ratios of hunter-harvested ducks are, at least in part, re- lated to conditions during the breeding season. Thus, understanding factors infl uencing productivity on breeding grounds are of primary concern for long-term conservation of breeding waterfowl populations in Maine.