During the last decades a rise in urbanization rates has taken place worldwide. It is expected that by 2050, 68% of the world population will live in urban areas. This is an important threat to biodiversity since urbanization results in a loss and fragmentation of the natural habitat and it can cause the extinction of several species. Impacts of the urbanization development cause changes in habitat, food resources, predators and competitors, and end up affecting the biology of bird populations present in urban areas. According to the SEO / BirdLife organization, the population of common sparrow (Passer domesticus) in Spain has suffered a decline of 21% from 2008 to 2018. In other European cities there is practically no individual of this specie. Factors such as the absence of cavities to nesting or the reduction of food quality, associated with the loss of vegetation in urban areas, have been the main causes of the decline on its population. In this study, we wanted to compare reproductive success of breeding birds couples in two mediums: natural and urbanized, and therefore to observe whether impacts of urbanization have any effect on the bird populations living in the Montilivi Campus area, where in 2018 60 nest boxes were placed. The data of the occupation of the nest boxes, the laying date, the clutch size, the physical condition and the development of the chicks were taken. An unexpected low proportion of occupied nest boxes resulted in a very low number of data, which reduced the obtaining of reliable and significant results. Finally, there were no significant differences between the reproductive parameters of the couples that had occupied nest boxes located in the natural environment and those who occupied nest boxes located in an urbanized one. The area considered as an urban one by this study, in fact, doesn’t present the proper characteristics of an urban area or its effects, but rather corresponds to a suburban area. Apart from what has just been mentioned, the little distance between the natural area and the urbanized area may have been another cause of the results obtained, as well as the low number of samples
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