Biodiversity in the gaps: The role of urban informal green spaces in supporting bird conservation in cities

Abstract

Urban environments are increasingly recognised as important for biodiversity conservation. While the ecological value of formal green spaces such as parks and nature reserves are well-studied, informal green spaces (IGS) – unplanned areas such as vacant lots, brownfields, and railway corridors – are gaining attention for their biodiversity contribution. Despite this, IGS remain under-researched and undervalued in conservation efforts. This study examines the ways IGS support the abundance and assemblages of bird communities in urban areas compared to formal green spaces. The study also investigates how different types of IGS – each with unique physical, social, and ecological features – support different bird species, exploring what drives these patterns. We conducted a city-wide study across Greater Melbourne, Australia, combining remote sensing data with citizen science bird surveys, using generalized linear mixed models to analyse the relationship between green space type and the probability of presence of different bird species. IGS, particularly railway easements and brownfields, supported a range of bird species – including threatened species – often underrepresented in formal green spaces. We provide insights into why certain land types may be more valuable than others for supporting urban birds, identifying key habitat features and foraging guilds associated with IGS. Finally, we make recommendations for enhancing biodiversity-friendly urban planning and land management on both informal and formal green spaces. While formal green spaces remain critical for urban conservation, our findings underscore the complementary value of IGS and the need to better integrate them into urban conservation planning.