Can opportunistic citizen sightings assist in the monitoring of an elusive, crepuscular mammal in an urban environment?

Spatial distribution of sarcoptic mange (Sarcoptes scabiei) in urban foxes (Vulpes vulpes) in Great Britain as determined by citizen science

Urban areas may support high densities of wild carnivores, and pathogens can strongly influence carnivore populations. Red foxes (Vulpes vulpes) are hosts of sarcoptic mange (Sarcoptes scabiei), which infects numerous species, and transmission can be density dependent. In Great Britain, urban red foxes (Vulpes vulpes) have recently increased in population density and undergone range expansions. Here we investigate corresponding changes in urban fox mange prevalence. We predicted a higher prevalence closer to historic epi/enzootics and lower prevalence where urban features reduce fox density and movements, i.e. large areas of public green space, and fragmented habitat, as measured by road length and urban perimeter shape complexity. We visually assessed mange symptoms from georeferenced images of urban foxes submitted online by the public, thus surveying private land on a national scale. We measured the proportion of foxes apparently showing mange and used SATSCAN to identify spatial clusters of high infection risk. Landscape features were extracted from urban layers in GIS to determine associations. Although mange was widespread, we identified a single cluster of high prevalence (37.1%) in Northwest and Central England, which exceeded double mean prevalence overall (15.1%) and mirrors the northward expansion of urban fox distribution. Prevalence was positively correlated with perimeter shape complexity and negatively correlated with distance to the nearest city with mange, although the latter association was weak. Our findings show that citizen science can effectively monitor diseases with highly visible symptoms and suggest that fox movements are influential in explaining spatial patterns of prevalence.