Mallard brood movements and survival in an urbanized landscape

Abstract

When selecting a nest site, mallards (Anas platyrhynchos) balance differing habitat requirements for the nesting and brood-rearing periods, such that the juxtaposition of these habitats in the landscape may influence the female's reproductive strategy and reproductive success. Mallard populations in the northeastern United States have declined since the mid-1990s, and increasing urban development in this region may pose risks to broods and cause high duckling mortality. We assessed mallard brood and duckling survival in the urbanized landscapes of Connecticut, USA, and evaluated whether differences in brood movements, home ranges, and habitat use in urbanized areas influence brood survival. We monitored 32 mallard broods from females with global positioning system (GPS) transmitters in Connecticut in 2021 and 2022. Apparent brood survival to 30 days (0.48, n = 29 broods) was comparable to previous estimates in the Northeast (range = 0.21–0.72), but individual duckling survival (0.18, n = 257 ducklings) was lower than many previous estimates for this region (range = 0.14–0.44), suggesting this parameter warrants continued evaluation because it may be contributing to population declines in Connecticut and the greater Northeast region. Mallard females demonstrated different reproductive strategies and seemed to prioritize either high-quality nesting habitat or proximity to high-quality brood-rearing habitat. High-quality nesting habitat is not necessarily near high-quality brood-rearing habitat, and 61% (17/28) of females moved their ducklings an average of 1.1 ± 0.9 km (SD) shortly after hatch to a brood-rearing site, often traveling along small streams. A similar proportion of successful (9/12) and failed (7/13) broods moved. We provide evidence of limited availability of brood-rearing habitat, as females moved long distances to brood-rearing wetlands and only 1 brood made additional inter-wetland moves. Management actions that create or modify nesting and brood-rearing habitat should consider connectivity between these sites; females may choose to nest away from wetlands to minimize exposure to predators but may depend on small streams for travel to brood-rearing wetlands.