Urban environments consist of a variety of landscapes which affect the amount of bird diversity present within a city. Often, ecological principles are not factored into urban residents’ choice of landscape design, resulting in a mosaic of different habitat types within one city. This is true for the cities of Fresno and Clovis in California’s Central Valley, where residential habitats are highly variable spatially and temporally. The ongoing drought, and water metering policies enforced since 2013, have forced residents to modify their landscaping practices. In the Urban Long-Term Research Area - Fresno And Clovis Ecosocial Study (ULTRA-FACES) we focus on the effects of changes in water use and landscaping on urban biodiversity. In 2010, using pre-metering data from 34 residential sites in the Fresno Bird Count (FBC), we showed that irrigation intensity, neighborhood poverty level, and grass height were key drivers of bird species richness. Here we focus on the post-metering years, and examine if 1) patterns of bird species richness have changed, and 2) the above factors continue to drive bird species richness five years later under significantly lower water use. We use FBC data from the same sites, along with measures of habitat cover and socioeconomics.
Results/Conclusions
We used an information theoretic approach to compare multivariate models combining social-ecological variables hypothesized to drive bird species richness within the 34 residential sites. We found strong support for a model combining mean tree height, percentage of bare dirt/mulch, understory shrub density, mean irrigation intensity, and property value as the best predictors of bird species richness (R2=0.45, F(27,7)=3.7812, p=0.0073). These results indicate that birds are responding to a different suite of variables after the implementation of water metering, with tree height and amount of bare dirt/mulch becoming more important than grass cover in determining species richness. We also found inter-annual variation in the strength and directionality of the relationship between property value and bird species richness, suggesting that the so-called luxury effect in urban biodiversity is not static, but changes with landscaping practices driven by institutional policy. Further time series analysis will allow us to examine changes in species composition in response to changes in the urban social-ecological system across the pre-/post-metering years. Understanding how socioeconomics and institutional factors affect the biotic structure of a city can inform us in managing city landscapes to support biodiversity.