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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.

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Urban expansion to rural and natural areas is a global process. Although several studies have analyzed bird community attributes along urbanization gradients, little is known on the impact of urbanization on temporal variability of bird communities. Rural areas show higher seasonal and interannual variability in environmental conditions and resources than do urban areas. Our objectives are to determine how seasonal and interannual variability in bird assemblages change along an urban-rural gradient, and how interannual variability in bird assemblages changes with season. Low seasonal and interannual variability of bird communities is expected in urbanized areas that show a process of temporal homogenization. Seasonal variability of bird richness and abundance were positively related to the percent cover of crops. Seasonal and interannual variability in community composition were positively related to coverage of herbaceous vegetation and crops, and negatively related to coverage of impervious areas. Interannual variability of bird richness and abundance were highest during the non-breeding season. We conclude that highly urbanized areas allow bird communities to have a more stable composition over time, promoting temporal homogenization. Our results emphasize that urbanization alters the temporal dynamics of resources and, therefore, the temporal variability of bird communities.

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Habitat colour gradients characterise urban areas: from green prevailing in the least urbanised areas dominated by lawn, shrubs and trees, to grey characteristic of heavily urbanised areas dominated by impervious surfaces. These changes may promote modifications in community composition and intraspecific colour changes in species occurring in urban areas. This review's objectives were: (1) to analyse reported patterns of animal colour change between urban and non‐urban areas; (2) to identify the main mechanisms underlying those patterns; and (3) to determine research bias and suggest future research directions. A bibliometric on animal colour patterns using Scopus resulted in 62 studies being found and their findings assessed. Most studies were focused on birds (N = 38) and were conducted in the Northern Hemisphere (N = 55), with 90% analysing intraspecific colour changes. Intraspecific studies found three main patterns: (1) urban melanism, with polymorphic species of insects, birds and reptiles showing darker colouration in urban areas than in non‐urban areas; (2) urban dullness, with carotenoid‐based plumage colours being duller in urban than in rural areas; and (3) a reduction in conspicuousness of sexually selected plumages in urban areas. Interspecific studies suggested that urban areas are filters for animal colours, promoting the colonisation of those species that increase camouflage or exhibit warning colours to predators. More studies are needed in the Southern Hemisphere and at the interspecific level to determine the role of animal colours in urban colonisation.

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