Relationships between birds, macro-litter, and vegetation in artificial urban wetlands in Greater Melbourne, Australia

Artificial urban wetlands provide valuable habitat to birds in extensive urban areas. However, these wetlands are often designed primarily for ecosystem services such as stormwater and wastewater remediation and tend to accumulate pollution. The potential impact of macro-litter pollution on birds in these ecosystems is poorly understood. We explored this relationship by surveying birds, macro-litter, and vegetation at 27 artificial urban wetlands across Greater Melbourne, Australia, during the austral summer of 2024/2025. The Dusky Moorhen (Gallinula tenebrosa) and 22 other wetland-dependent bird species were the most common; however, we also recorded woodland, shrubland and forest-dependent species. Litter was recorded at all wetlands, with food-related plastic packaging the most common, and Litter Index ratings were generally poor. Generalised linear modelling revealed little evidence of relationships between community bird metrics and macro-litter loads, suggesting that litter loads were not a major determinant of bird communities. Further, of the 22 species examined, the Eurasian Coot (Fulica atra) showed the strongest negative relationship with increasing litter density. Additionally, a potential relationship between macro-litter loads and vegetation densities was observed. Given that many bird species are reliant on vegetation for resources including nesting and foraging, further investigation of the potential indirect impacts of macro-litter on vegetation and other key resources to bird life is needed. Our findings highlight the importance of artificial urban wetlands as hotspots for birds and macro-litter and have important ramifications for the management of the bird–litter relationship in non-marine environments.