Effects of urban noise, irrigation, and neighborhood socioeconomics on bird communities in Fresno, California

Background/Question/Methods

Ecological and socioeconomic variables must be combined to explain the composition, distribution, and population dynamics of urban wildlife. We have shown that property value and yard irrigation drive plant and bird diversity in Central California’s Fresno-Clovis Metro Area (FCMA). Here we focus on how three local scale factors—anthropogenic noise, proximity to wetspace (flood control basins), and greenspace (parks)—affect bird abundance and species richness. We analyzed bird counts (at 238 random points) by Fresno Bird Count (FBC) volunteers with concurrent noise level measurements and distance to nearest greenspace and wetspace.

Results/Conclusions

Sites with extreme noise levels had fewer species (5.4 spp on average) than sites with moderate (7.2 sp; ANOVA, p=0.05) or no noise (7.4 sp; p=0.03). Noise had no effect on bird abundance (p=0.09). Proximity to wetspace had a significant effect on species richness (R²=0.057, p<0.0002), but not on abundance (R²=0.007, p=0.21). Proximity to parks showed the same trend for species richness (R²=0.016, p=0.05) and abundance (R²=0.0024, p=0.45). These effects persist after controlling for property value and yard irrigation levels, both previously shown to drive bird diversity and abundance.

While socioeconomics explain bird diversity across FCMA, local (within city) variation in diversity is driven by landscape (green or wet spaces) and behavioral (noise) variables. While more food in cities increases bird populations, species composition is more sensitive to noise and landscape factors other than food. Urban ecology research and policy must take more multiscale, multivariate, landscape-based, and taxon specific approaches to better manage cities for biodiversity.