Nestedness of bird assemblages on urban woodlots: Implications for conservation

Nestedness is a pattern frequently observed in fragmented systems and has important implications for conservation. The few existing nestedness studies in urban landscapes have focused on the resident and breeding birds, while little attention has been paid to the wintering birds. Using distribution data of 60 bird species collected on 20 urban woodlots in Hangzhou, China, we tested for the existence of the nestedness and the underlying mechanisms for breeding birds and wintering species separately. We used the line-transect method to survey bird occupancy and abundance on 20 woodlots. We used two recently developed metrics, WNODF and NODF, to estimate nestedness. We used partial Spearman rank correlations to examine the associations of nestedness and habitat variables (area, isolation, habitat richness and human disturbance). We also used information-theoretic methods based on Akaike Information Criterion (AIC) to determine ecological processes underlying nestedness. The community compositions of breeding birds and wintering species were all significantly nested. Habitat nestedness is the main driver of species nestedness for all the bird assemblages. Human disturbance played an important role in the development of species nestedness for breeding birds, but not for wintering species. Nestedness of all the bird assemblages was not due to passive sampling, selective extinction or selective colonization. From a conservation viewpoint, our results indicate that we should protect woodlots with diverse habitats priorly and refrain from using breeding birds and wintering species as surrogates for each other in developing conservation planning.

► The assemblages of breeding and wintering birds were all nested on urban woodlots.
► Habitat nestedness was the main driver of species nestedness for the bird assemblages.
► Noise pollution exerted stronger effects on breeding birds than wintering birds.
► Breeding birds and wintering birds were nested, but for different reasons.