IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Rebelo Ifr n, N. | |
| Mechanisms of occupation and adaptation, costs and benefits of a contemporary process of urbanization in Aves | |
| 2017 Full Book | |
Humans have colonized most of the Earth's ecosystems, which has led to a progressive modification of natural environments. Urbanization process is a particularly drastic form of habitat modification in which most species fail to persist. However, many of them are able to adapt to these new environments and even thrive successfully, becoming many times more abundant than in rural surroundings. This scenario has led a growing interest in understanding the processes and mechanisms involved in the successful colonization of urban habitats, as well as the implicated costs and benefits. The Burrowing Owl (_Athene cunicularia_) is a small raptor that spread throughout the American continent, where it shows different population tendencies. While in the northern hemisphere habitat loss, coupled with other threats, has led to the decline of its populations, in the southern hemisphere it is a frequent species lives in natural, semi-natural and urbanized environments. In this thesis, a long-term study of a population of Burrowing Owl has been carried out in the city of Bah¡a Blanca and in the surroundings rural areas. Population monitoring was done by capturing and banding individuals, both in urban and rural areas. The marked of individuals allowed it to estimate both demographic parameters (fundamentally survival and productivity) as well as physiological estimators in order to determine the costs and benefits of occupying urban environments. The objectives of this thesis were: 1) to evaluate the habitat breeding selection taking into account the availability of natural and urban habitats, 2) to analyze the long-term stress response in urban and rural individuals, evaluating their relationship with the fitness of individuals in both environments, and 3) to compare the demographic parameters of the species (survival, breeding success, productivity), taking into account the dispersion of individuals among habitats. The results indicate that the release of predators that occurs in urban environments (lower richness and abundance of predators than in rural environments) may explain the positive selection of this habitat by the species, as well as the higher density of breeding pairs compared to observed in the most natural habitat. Despite differences in ecological conditions between urban and rural environments, urban individuals did not show higher levels of chronic stress than their rural conspecifics. This suggests that life in the city does not constitute an additional source of stress for organisms. Moreover, adult individuals reached higher survival values in these habitats compared to rural individuals, which was not observed for juvenile individuals whose survival in urban and rural environments was not statistically different. Different survivals of adult individuals in both habitats evidenced a quadratic relationship between stress levels and survival of individuals, with higher mortalities in individuals with low and high levels of feather corticosterone. Finally, differences were also found in the reproductive parameters of urban and rural individuals, with higher mean values for the urban ones. It is worth mentioning the interaction between habitat and years, which shows the stability of productivity values for urban individuals in the face of fluctuations observed in rural areas. In summary, the results suggest that cities have an important conservation role for species that are able to colonize them successfully, which is fundamental when considering species whose natural habitats are threatened or in decline, such as temperate grasslands. |
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