Factors influencing wintering turfgrass field use in Atlantic brant

Atlantic brant Branta bernicla hrota increasingly use turfgrass fields, such as baseball fields and golf courses, throughout their wintering range. Most studies have focused on their primary food source, submerged aquatic vegetation, while studies of other goose species worldwide have examined field use in different contexts, including agricultural fields and use during staging and migration. These studies have generally supported the importance of extrinsic factors, such as field size and distance to the roost, as well as variable effects of intrinsic factors, including forage quality and quantity, in determining field use. However, no studies have examined the system of turfgrass fields used by Atlantic brant in the United States. We sampled turfgrass fields during the winters of 2021–2022 and 2022–2023 in New Jersey and New York, USA, and used Bayesian hierarchical modeling to explore the importance of field and grass characteristics in predicting both field use and the intensity of use by brant in this urban ecosystem. We found that extrinsic characteristics – field area, distance to water, and distance to the roost – had the strongest effects on field use. The biomass of live grass and dead grass were also important predictors in both models. In contrast, grass height, weed biomass, clover biomass, carbon–nitrogen ratio, and energy density had weak effects that varied in strength and importance among models. These results are consistent with previous studies of geese in other systems, despite differences between urban turfgrass ecosystems and natural or agricultural habitats. Our findings indicate that, within urban turfgrass systems, landscape‐level characteristics may outweigh traditional forage‐quality metrics in driving habitat use, and they may help inform future management of brant if submerged aquatic vegetation declines or population dynamics change.