Urban bird diversity: does abundance and richness vary unexpectedly with green space attributes?

Urban bird diversity has been shown to be a useful indicator of overall biodiversity in urban green spaces. Attributes of green spaces (size, location and age) vary within a city and can influence bird diversity. To understand the relationship between bird diversity and green space attributes, we assessed bird abundance and richness in several green spaces in Reykjavik, Iceland. Fifteen green spaces were selected, representing different size categories (small: <5 ha and large: 7–41 ha) and different locations within the urban sprawl (central and suburban). Thirteen transect surveys were conducted at each park from March to September 2020. Abundance, species richness, the Shannon diversity index and evenness were compared across parks. Abundance, Shannon index and evenness were significantly higher in large, intermediate-aged parks with residential urban contexts (P < 0.05). Richness did not vary significantly with park size but was significantly higher in old- and intermediate-age parks that were centrally located (P < 0.005). Bird diversity did not vary significantly over the survey season. For abundance, our results were expected: the larger the park, the greater the abundance. However, contrary to most studies, the suburbs of Reykjavik had less richness than the city center. Furthermore, park size was not relevant for richness, which is the main factor in other cities (e.g. London, Boston). These differences in response indicate that abundance and richness should be considered simultaneously when monitoring urban bird diversity. Lastly, small urban parks (<5 ha) should not be disregarded in urban planning, especially in high latitude cities.