Using community gathered data to detect differences in bird community composition across the urban gradient in the Seattle area

Background/Question/Methods

Bird community composition varies across urban gradients as defined by key social and environmental variables. Previous studies have identified social and economic variables including income, race, and ethnicity, as particularly important determinants of bird community composition, largely because these variables dictate plant communities in urban areas. Population density, building density, vegetation cover, and the proportion of impervious surfaces also vary across the urban gradient and influence bird community composition. The goal of this study is to examine if bird abundance data collected by citizen scientists can be used to detect changes in bird community composition along the urban gradient in Seattle, WA. Bird abundance data (2002-2010) was downloaded from eBird, an online portal operated by the Cornell Lab of Ornithology and the National Audubon Society that allows professional and recreational birders to report their observations for use by the scientific community. Key socioeconomic and landscape variables, including land cover type, race and ethnicity as a percentage of total population were derived from publically available data sources. These variables were associated with individual bird abundance observations based on location using ArcGIS. The resulting dataset was analyzed in R using the Bray-Curtis distance matrix and PERMANOVA.

Results/Conclusions

Our results suggest that bird abundance data collected by citizen scientists does not detect the same changes in bird community composition along the urban gradient found in other peer-reviewed papers. We found that the season in which data was collected was an important indicator of bird community composition, while year, time, and effort spent were not significant. After accounting for the effects of season, the only significant social or environmental variable was the percent of Asians living in the census block. This contrasts with published studies. For example at least three studies, including one from Vancouver from 2005, found positive correlation between bird community composition and family income. Other studies have found increased number of plant species with higher income and lower with percent Hispanic. This supports the published results as urban birds are highly reliant on vegetation structure. Further research is needed to understand why data collected by citizen scientists detected different changes in bird community composition along the urban gradient than those reported in the literature. It is important to resolve these concerns, since involving urban citizens with nature promotes successful biodiversity conservation in both urban and wilderness areas.