Effect of Urban Sprawl on the Diversity of Bird Species in Bay Area Parks Sara May Taylor Abstract Population growth in the San Francisco Bay Area has led to significant urban sprawl Although habitat destruction has been quantified in the past the mechanisms through which biodiversity is influenced by different levels of urbanization and how such effects can be quantified and analyzed have been largely unexplored The effects of three different levels of urbanization associated with urban sprawl urban suburban and rural on avifaunal diversity were examined using three different methods of analysis Nine parks were selected three for each level based on adjacent human population density Data were collected in the spring when each site was visited for three two hour sessions Methods of data analysis used were 1 a diversity index and richness value for each park 2 a ratio of generalist species to specialist species present in each park and 3 a diversity index for three regions within each park the edge the interior and areas near human disturbance These methods were employed to determine diversity and special differences based on level of urbanization and region within each park A significant difference was found between urban suburban and rural park diversity indices however no difference in richness was found between parks A positive correlation was found between the generalist to specialist ratio and adjacent human population density demonstrating a significant increase in generalist species with increases in population Differences in diversity were found between park regions showing urban parks have higher diversity at their edges and a higher number of generalists near human disturbance than rural parks Introduction As cities become excessively overcrowded development begins to spill outward in a pattern known as urban sprawl The growth of the city within its boundaries already destroys essential habitat for a number of animals which must then adapt seek refuge in the surrounding areas or die Furthermore if the surrounding areas are undergoing habitat degradation as well due to urban sprawl survival options become even more limited Marzluff 2001 One option for local wildlife is to continue to move outward as suburban cities develop into urban ones Blair 1996 Should this be the case an upsurge in density of wildlife as the human population density decreases would result following the pattern of urban sprawl on a radial line outward from the city center This study examines this assumption s accuracy by testing whether or not this relationship is indeed occurring in the San Francisco Bay Area California and to evaluate the efficacy of chosen methods to detect diversity changes in the field Urban sprawl is ever present and increasing in almost every major city in the country Evaluating any detrimental effect the process has on a community s endemic wildlife may help eventually limit such a growth pattern and assist in implementing policies for regions not yet encroached upon by urban development Where biologists once worked on ways to evaluate habitat destruction in cities Gavareski 1976 Janzen 1983 Barrett et al 1994 now the job has become that of the urban planners Tilghman 1987 Cicero 1988 Lim and Sodhi 2003 The two dissimilar occupations have built a large information base regarding the remaining habitat patches within the human matrix which will ultimately help create healthier communities for both development and wildlife Alberti et al 2001 Unfortunately few studies of this kind have focused on the San Francisco Bay Area and these studies exhibit a lack of power in analysis methodology Therefore what is required at this time is both an accurate assessment of the effect of urban sprawl and a potent study method The Bay Area in Northern California is one of the best places in the United States to study urban sprawl Human population density varies as a function of the distance from the city of San Francisco Figure 1 generally decreasing in density as one moves away from the city center Figure 1 Human population density in the San Francisco Bay Area Values were obtained from the US Census Bureau s Census 2000 data With the Pacific Ocean to the west there exists a gradual decline in population outward from the city far to the north south and east as cities and suburbs spill out into surrounding rural areas Many local communities support conservation and there are a variety of nature areas and parks in these areas each one adjacent to a varying degree of human population density These parks become ideal locations to perform population analyses because they are quite similar in climate vegetation and available recreation yet differ in their proximity to urbanization and not coincidentally in degree of anthropogenic disturbance Janzen 1983 Birds were chosen as a measure of wildlife diversity within the chosen ecosystems Birds are a much utilized indicator phylum in urban studies Beissinger Osborne 1982 Tomialojc 1998 Fernandez Juracic 2000 Marzluff 2001 Lim and Sodhi 2003 primarily due to the ease of data collection though additional knowledge about these animals makes them ideal study subjects They are wild animals about which much is known including habitat requirements migratory patterns and identification techniques Cramp 1992 Stokes and Stokes 1996 Three measurement methods of measuring were employed to quantify the abundance and richness of bird species in nine Bay Area parks Figure 2 each differing in level of urbanization The parks chosen and their specific urbanization categories based on adjacent HPD are as follows Golden Gate Park San Francisco urban Lake Merritt Oakland urban Strawberry Creek Fire Trail Berkeley urban Joaquin Miller Regional Park Alameda County suburban Castle Rock Regional Park Walnut Creek suburban Pt Pinole Regional Shoreline Richmond suburban Coyote Hills Regional Park Fremont rural Mt Diablo Black Diamond Trail Clayton rural and Morgan Territory Regional Park Contra Costa County rural Figure 2 Site locations in the San Francisco Bay Area map is approximate not to scale Any significant changes in species diversity detected between parks could be used to support theoretical conclusions on the effect of urban sprawl on local wildlife In addition if one method or combination of methods proves to be a superior approach such information could be used when monitoring park diversity in the future Methods Nine sites were selected based on their location with
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