Abstract:

Aim: To examine the impact of habitat fragmentation stemming from urbanization on bird diversity and distribution patterns.
Methods: We surveyed bird assemblages on 26 fragmented woodlots with areas of 0.3-290.4 ha in Huaxi University Town, Guizhou Province from April to August between 2017 and 2019. We surveyed birds by establishing line transects in each woodlot, with transect length roughly proportional to the woodlot area. We surveyed each line transect 10 times over the course of the study period, and recorded birds detected within 50 m of either side of the line transects.
Results: In total, we recorded 78 bird species belonging to 11 orders and 37 families. Species of Oriental origin, Palaearctic origin, and widespread species accounted for 56.4%, 32.1%, and 11.5% of observations, respectively. We observed one species endemic to China. After excluding birds detected as fly-overs (e.g., swallows and swifts), non-forest dwelling birds (e.g., waterbirds), and birds that were only recorded once in the survey, we found that the number of bird species in different woodlots ranged from 12 to 55 species, with an average of 23.2 ± 10.5 species per woodlot. Linear regression analysis showed that bird species richness was significantly positively correlated with woodlot area, with larger woodlots having higher bird richness. A metric of isolation, measured as the distance to the nearest neighboring woodlot, had no significant effect on bird species richness. The analysis of nestedness, based on the metric WNODF (weighted nestedness metric based on overlap and decreasing fill), conducted on the species-by-site abundance matrix, revealed that the observed WNODF for sites of birds was significantly lower than expected from the null model, indicating that bird assemblages were anti-nested among the woodlots.
Conclusion: Our results suggest that plant richness, food resources and breeding conditions in small woodlots may be diminished compared to larger woodlots, making it difficult for some bird species to meet their survival needs. However, the relatively short distance between woodlots in our study sites combined with the stronger dispersal ability of birds may mask the biological importance of isolation. The anti-nested structure of bird communities may be the result of larger differences in species composition between woodlots being driven by environmental filtering, interspecific competition, or priority effects, but further research is needed to determine the likely causal mechanism of anti-nestedness. Nevertheless, given that rapid urban expansion has caused substantial habitat fragmentation in recent decades in our study area, we recommend that habitat integrity should be prioritized and maintained in urban planning when possible, and that fragmented woodlots of different sizes be protected.

Key words: patch, area, isolation, nestedness, species richness, biodiversity, urbanization