Not too small to matter: park area, bird diversity, and nestedness in pocket parks of an arid city

Urbanization is a major driver of biodiversity loss, making urban green spaces increasingly important for conservation. In arid cities, where water scarcity limits the establishment of large parks, small green areas may be particularly relevant. We examined how park attributes and anthropogenic noise influence taxonomic and functional bird diversity across 15 pocket parks in La Serena, Chile. Additionally, we assessed whether bird assemblages exhibited nestedness along the park-area gradient and whether this pattern could be explained by passive sampling, park characteristics, or species traits. We recorded 29 bird species. Species richness and Shannon diversity increased with park area, whereas noise had weak negative effects. Functional richness increased with park area, functional evenness declined, and functional divergence showed no clear response. Bird assemblages exhibited strong nestedness, with smaller parks supporting subsets of species found in larger ones. However, nestedness exceeded expectations under an equiprobable null model but not under a fixed–fixed model, indicating that the observed structure could be explained by differences in park richness and species occurrence frequencies. Passive sampling did not explain the area–richness relationship. Park area and tree abundance were associated with nestedness rank, whereas species rank varied with habitat preference but not morphological traits. Larger parks supported greater taxonomic diversity, while smaller parks primarily retained widespread, urban-adapted species. These findings highlight the importance of maintaining larger green spaces and tree abundance to conserve urban bird diversity in dryland cities.