Contenuto scaricabileScarica il pdf
Avian communities in two urban environment and a natural habitat in Simi Valley, Southern California
Bird communities of two urban habitats of different ages and a natural habitat in Simi Valley, California were compared to determine whether the urban habitats were ecologically equivalent to the original habitat of an area as it existed prior to urbanization. The natural study site was carefully selected so as to closely resemble the original habitat of the urban study areas. The natural habitat supported the highest number of species (31), whereas the older urban area only supported 10 and the younger area only 8 species. Accordingly, species diversity indices were highest for the natural area (H' = 3.3, J' = .96) and much lower for the urban areas (H' = 1.7 and 1.5, J' = .74 and .72). Analysis of population densities showed the highest number of individuals of resident species to be in the older urban area (721/100 ha) closely followed by the natural area with 696/100 ha, and with only 277/100 ha in the younger urban area. The large difference between the two urban study areas was probably due to a difference in age of the developments (birds are still invading the younger, less well vegetated area), and closer spacing of houses (less space and more disturbance to bird activities in the younger area). In general, granivorous and water-dependent birds were the most successful species in invading the urban habitats, whereas insectivorous birds tree cavity nesters, ground-dwellers and birds of prey were generally absent. For those species that are able to adjust to new nesting habits and additional disturbance factors, the urban habitat offers increased food and water and many perching and nesting sites. Apparently urban habitats are capable of supporting high densities of a limited number of species, but invite only a small fraction of the bird species previously occupying the area. They are, therefore, not equivalent to the original habitat present in an area before urbanization.