The public-private divide and seasonal variation shape bird diversity in greenspaces of two neighboring midwestern USA cities

Greenspaces are increasingly valued for supporting biodiversity in urbanized landscapes. Previous research efforts have emphasized the importance of public land such as parks and nature preserves for biodiversity, yet private yards in residential neighborhoods also have great potential for species conservation. Our study considered the importance of adjacent public and private greenspaces for urban bird diversity. We surveyed birds in public parks (n = 39) and private yards (n = 41) distributed across neighboring twin cities (Champaign and Urbana) in Illinois, USA, to assess potential differences in bird diversity across: (1) the public-private divide; (2) seasons (winter vs. summer); and (3) the two cities. We found a seasonal interaction across the public-private divide. In summer, communities in private yards were a subset of those found in public parks, whereas in winter, both private yards and public parks hosted equally diverse yet distinct species assemblages. Between the two cities, Urbana supported greater bird diversity and a distinct species assemblage compared to the warmer, more urbanized city of Champaign. Our results demonstrate that both public parks and private yards play key roles in supporting native bird diversity, but also highlight that these roles can shift across seasons. Furthermore, we show that neighboring cities within the same conurbation can differ substantially in bird community structure and diversity. Our findings reinforce the importance of maintaining heterogeneous landscape mosaics and combining land sparing and land sharing approaches to maximize bird diversity in urban areas.