Shared population trends but no annual synchrony in duck species across Europe and North America

Abstract Few studies have explored population dynamics of species sharing life-history traits and common environmental drivers but living in widely separated regions or continents. Large-scale climate cycles can impact habitats and populations over broad geographic areas and may act as global forces shaping animal population dynamics. We tested for synchronous population dynamics of eight ecologically equivalent duck species in Western Europe (WEU) and central North America (NA) from 1976 to 2019. We investigated the extent to which the Atlantic Multi-Decadal Oscillation (AMO) may have induced shared climatic conditions on the breeding areas of these populations and whether the index was correlated with duck population dynamics. Evidence of annual and long-term population synchrony was assessed by estimating correlation in annual growth rates and population abundances, respectively. Shared (increasing) long-term trends in WEU and NA were found in four species-pairs, but no species-pair had synchronous population growth on an annual basis. Three species-pairs sharing trends were positively correlated with the AMO index which increased during the study period. Positive cycling of the AMO was correlated with increased temperature and precipitation in breeding areas of both continents, which may have produced favorable conditions (earlier springs, more ponds) for some duck populations. Differences in the local effects of weather on environmental conditions and other continent-specific extrinsic factors may mask annual synchrony in the response of continental populations to climate. Potential links between the AMO trends and extrinsic factors such as shared changes in anthropogenic drivers (e.g., climate and land use change) should be addressed in future studies.