ABSTRACT
Biological invasions are often one of the main causes of global biodiversity loss. Parrots are among the most globally traded taxa and have successfully invaded urban areas. Studies analyzing alien parrot-habitat relationships are scarce in cities of the southern hemisphere. This study aims to determine habitat characteristics influencing exotic parrot species richness, presence, and composition in urban parks in Buenos Aires City and to analyze variations during breeding and non-breeding seasons. A total of 35 parks were sampled during the breeding season and the non-breeding season, and habitat variables at local and landscape scales were measured. Parrot species richness was positively associated with tree species richness and a shorter distance to the La Plata River throughout the year. During the non-breeding season, parrot species richness increased in parks with a higher abundance of tree genera such as Eugenia, Podocarpus, Olea, and Washingtonia. However, during the breeding season, parrot species richness decreased with increased environmental noise. Taxonomic richness was higher during the breeding season. The occurrence of different species and composition depended differentially on each variable, and it varied between seasons. Our findings suggest that exotic parrot richness and presence may be influenced not only by tree diversity and park proximity to green corridors but also by specific exotic tree species providing resources for the parrots. Future urban green space designs should prioritize native tree planting to support local biodiversity over exotic trees that benefit invasive bird species.
ABSTRACT
BACKGROUND: A scarcely studied consequence of urbanization is the effect of temporal stabilization of the environment on bird communities. This alteration is thought to dampen environmental variations between day and night, seasons and years, promoting a temporal persistence of bird composition in urban areas. The aim of this study was to review current evidence of temporal stabilization of biotic and abiotic factors in urban environments and the potential effects of such stabilization on temporal variation of bird species presence at different temporal scales. METHODS: I selected the literature by searching published articles and book chapters using Scopus and Google scholar. I only included articles that compared the temporal variation of bird composition or resources between different levels of urbanization. RESULTS: In general, there is evidence of temporal stabilization of abiotic and biotic factors at the three time scales considered. At the diurnal scale, the main factor considered was artificial light in the context of light pollution. At the seasonal and interannual scales, several case studies found a smaller temporal variation of primary productivity in urban than in natural and rural areas. Bird species composition showed more stabilization in urban environments at the three temporal scales: (1) several case studies reported bird activity at night, associated with artificial light; (2) studies in urban parks and along urbanization gradients showed smaller seasonal variation of bird composition in the more urbanized areas; and (3) in general, case studies along urbanization gradients showed smaller interannual variation of bird composition in the more urbanized areas, although some studies showed no relationships or opposite trends than expected. DISCUSSION: The published evidence suggests that urban areas dampen the natural cycles at several temporal scales. The stabilization of biotic and abiotic factors, such as light, temperature, food and habitat structure, is desynchronized from natural diurnal, seasonal and interannual cycles. However, there is a dearth of long-term comparisons of bird composition and studies that simultaneously analyze the relationship between resources and bird composition stabilization at the seasonal and interannual scales. More research is needed in the Southern hemisphere, where there is a lack of studies dealing with the seasonal and interannual variations of primary productivity along urbanization gradients and nocturnal activity of bird species. A future research agenda should include differentiation of spatial and temporal homogenization of avifaunas.
