A continental measure of urbanness predicts avian response to local urbanization

Understanding species-specific relationships with their environment is essential for ecology, biogeography, and conservation biology. Moreover, understanding how these relationships change with spatial scale is critical to mitigating potential threats to biodiversity. But methods which measure inter-specific variation in responses to environmental parameters, generalizable across multiple spatial scales, are lacking. We used broad-scale citizen science data, over a continental scale, integrated with remotely-sensed products, to produce a measure of response to urbanization for a given species at a continental-scale. We then compared these responses to modelled responses to urbanization at a local-scale, based on systematic sampling within a series of small cities. For 49 species which had sufficient data for modelling, we found a significant relationship (R2 = 0.51) between continental-scale urbanness and local-scale urbanness. Our results suggest that continental-scale responses are representative of small-scale responses to urbanization. We also found that relatively few citizen science observations (~250) are necessary for reliable estimates of continental-scale urban scores to predict local-scale response to urbanization. Our method of producing species-specific urban scores is robust and can be generalized to other taxa and other environmental variables with relative ease.