Sub-tropical bird responses to seasonal variations and urbanization pressures along rural-urban gradient in...

Urbanization transforms ecosystems by affecting biodiversity and reducing environmental variability. To assess these changes, the normalized difference vegetation index (NDVI) is commonly used as a vegetation metric to examine habitat quality and its relationship with species richness in urban habitat. This study evaluated the usefulness of NDVI in predicting temporal and seasonal shift in avian communities by examining species richness, composition, and diversity across urban (UR), peri-urban (PE), and rural (RU) habitats using PCA ordination. Bird surveys were conducted once per month throughout the study period across the urbanization gradient during both breeding and non-breeding seasons. Seasonal and annual NDVI values were calculated, and regression analysis (as data were normally distributed) used to test the relationship between NDVI patterns and avian diversity. Urban areas exhibited lower annual NDVI values but smaller seasonal changes, whereas rural sites showed higher NDVI values with greater seasonal fluctuations. Seasonal variations of NDVI were marked by lower values in urban areas (UR) during both seasons (mean seasonal variation = 0.32) and higher seasonal fluctuations in rural areas (RU) (mean seasonal variation = 0.18). Urban sampling sites with high vegetation cover (mean NDVI = 0.68) exhibited higher NDVI values and the lowest seasonal variation in both seasons. Bird richness displayed a significant positive regression with an increase in mean NDVI during breeding (y = 5.1 + 22.32*x, p < 0.01) and non-breeding seasons (y = 3.0 + 21.65*x, p < 0.01). However, species richness showed a negative association with seasonal NDVI during both the breeding (y = 19.2 + -108.01*x, p < 0.01) and non-breeding seasons (y = 21.1 + -122.31*x, p < 0.01). The findings indicate that urban areas (UR) have higher seasonal stability of avian fauna than in rural areas (RU), with urban areas showing a more homogenized seasonal pattern. The study suggests that urbanization alters habitat structure, resulting in reduced seasonal dynamics and primary productivity, ultimately leading to more stable but less diverse avian communities in urban environments. These results underscore the importance of maintaining vegetation cover in urban areas and conserving rural zones to preserve avian biodiversity.