Bird community responses to different urban conditions in La Paz, Bolivia

Abstract

Our main objective was to contribute to a better knowledge of bird communities in La Paz, and to describe to some extent how they are affected by urbanization. We address the following questions: a) How are bird species richness and abundance influenced by different local habitat and urban development measures, and by different levels of urbanization?; b) How do these measures influence species composition?; and c) How much of the variation in species composition can be explained by these measures? For the first question, we predict that species richness and abundance will decline with increasing levels of urban development. For the second question, we predict that few bird species will be found in highly urbanized environments, compared to higher number of species in environments with low levels of urbanization. We expect the habitat and urban development measures to explain high percentages of variation in species composition.Urbanization alters ecosystems worldwide, but little is known about its effects in the Neotropical region. In the present research we examined the relative influence of different levels of urbanization and of some urban development measures on bird species richness, abundance and composition. We surveyed 104 observation stations at which we collected data on the relative abundance of bird species, and also data on seven environmental variables as measures of urban development and human activity. We registered 57 native bird species. Bird species richness and bird abundance increased with lower urbanization levels. Both variables were positively related to vegetation cover and native vegetation, and negatively to built-up cover, abundance of Rock Pigeon (Columa livia), pedestrian rate and car rate. A canonical correspondence analysis produced a significant model that explained 37% of the total variation in species data. This analysis segregated bird species along two important gradients: urbanization and elevation. The most urbanized areas were dominated by a few synanthropic species tolerant to human disturbance, such as Rufous-Collared Sparrow (Zonotrichia capensis), Eared Dove (Zenaida auriculata) or Chiguanco Thrush (Turdus chiguanco). Areas with lower urbanization levels had more species typically associated with native vegetation, such as Plain-Mantled Tit-Spinetail (Leptasthenura aegitaloides) or D’Orbigny’s Chat-Tyrant (Ochthoeca oenanthoides), among others. Elevation had a significant influence in structuring bird communities, with some species restricted to higher elevations and some to lower elevations. Although changes in elevation had an important influence, urbanization had a stronger effect on structuring bird communities. This study provides valuable information and an important baseline for future studies