Nature doesn’t stop at the doorstep of a town or city. Ecosystems exist the world over, though they vary in their health, diversity, and other properties. Therefore, urban environments do have a capacity to serve the ‘needs’ of species other than humans, and in this case an urban green space’s ability to meet the ecological needs of bird species is assessed.
According to past research, in many urban environments – particularly those with a low abundance of trees and a lack of structural diversity – bird species that can be found are usually generalist ones. Therefore, there is scope to use bird species diversity in an urban environment to indicate its overall green space structural diversity.
This study looked at sixteen green spaces (including woodlands) within two cities in Italy: Milan (13), and Bari (3). The selected green spaces were clustered into three categories – the three largest green spaces in Milan, the three largest in Bari, and the remaining ones in Milan. Within the selected green spaces, bird species were counted over the course of a breeding season at eighty different point-counts, and the great tit (Parus major) and serin (Serinus serinus) were used as the principal indicator species – this was because both species were observed at over fifty of the point-counts, across Milan and Bari.
From the survey, a total of 56 bird species were recorded, which amounted to a total of 4,393 individual specimens. Many of the species observed were either ‘forest species’ (including the wren (Troglodytes troglodytes), short-toed treecreeper (Certhia brachydactyla), jay (Garrulus glandarius), and great spotted woodpecker (Dendrocopos major)) or ‘farmland species’ (including the stonechat (Saxicola torquata) and red-backed strike (Lanius collirio)). Other species observed were far more generalist in nature, and included the feral pigeon (Columba livia), hooded crow (Corvus corone), and starling (Sturnus vulgaris), though ‘aquatic species’ were also identified because of the presence of ponds (including the little grebe (Tachybaptus ruficollis) and great crested grebe (Podices cristatus)).
Having analysed the data captured, the authors concluded that abundant and more mature tree stands supported a great variety of bird species. However, the connectivity between the sites observed, as well as their connectivity to areas of nearby grassland, open space, hedgerow amongst agricultural land, ponds, and smaller woodland sites not surveyed, also played a discernible role in how many bird species were observed at a site – in essence, if a site contributes to a larger ‘network’ of sites, it is more likely to support a greater array of bird species, whilst a very isolated site will provide the opposite.
Therefore, for urban environments to support a wide variety of bird species beyond simply the generalist species, then there needs to be: (1) areas of extensive tree cover with mature specimens within, (2) areas of other land type (such as grassland and hedgerows within agricultural fields, though I would posit that street trees would also be critical), and (3) a high degree of connectivity between these different land types (supplemented by larger street trees, perhaps).
Thus, if an area of green space can be seen only to support generalist bird species such as the feral pigeon and hooded crow, there is a marked probability that the site lacks connectivity to other green spaces, and is also not situated within a network of a greater variety of land types.
Source: Sanesi, G., Padoa-Schioppa, E., Lorusso, L., Bottoni, L., & Lafortezza, R. (2009) Avian ecological diversity as an indicator of urban forest functionality. Results from two case studies in Northern and southern Italy. Journal of Arboriculture. 35 (2). p80-86.
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