Abstract
Globally there are many examples of synanthropic carnivores exploiting growth in urbanisation. As carnivores can come into conflict with humans and are potential vectors of zoonotic disease, assessing densities in suburban areas and identifying factors that influence them are necessary to aid management and mitigation. However, fragmented, privately owned land restricts the use of conventional carnivore surveying techniques in these areas, requiring development of novel methods. We present a method that combines questionnaire distribution to residents with field surveys and GIS, to determine relative density of two urban carnivores in England, Great Britain. We determined the density of: red fox (Vulpes vulpes) social groups in 14, approximately 1km2 suburban areas in 8 different towns and cities; and Eurasian badger (Meles meles) social groups in three suburban areas of one city. Average relative fox group density (FGD) was 3.72 km-2, which was double the estimates for cities with resident foxes in the 1980’s. Density was comparable to an alternative estimate derived from trapping and GPS-tracking, indicating the validity of the method. However, FGD did not correlate with a national dataset based on fox sightings, indicating unreliability of the national data to determine actual densities or to extrapolate a national population estimate. Using species-specific clustering units that reflect social organisation, the method was additionally applied to suburban badgers to derive relative badger group density (BGD) for one city (Brighton, 2.41 km-2). We demonstrate that citizen science approaches can effectively obtain data to assess suburban carnivore density, however publicly derived national data sets need to be locally validated before extrapolations can be undertaken. The method we present for assessing densities of foxes and badgers in British towns and cities is also adaptable to other urban carnivores elsewhere. However this transferability is contingent on species traits meeting particular criteria, and on resident responsiveness.
Highlights
Urbanization is a major cause of land use change worldwide, typically resulting in the loss of biodiversity [1]
To determine whether fox sightings density (FSD) from Scott et al.’s (2014) national fox sightings study could constitute a proxy for fox group density (FGD) and allow extrapolation to other cities using estimates from comparable urban areas, we explored the relationship between these two non-normally distributed variables using Spearman’s rank correlation
Of ~30,000 questionnaires distributed across a total survey area of 17km2 across eight towns/ cities, 5645 responses (19%) were received; an average response of 403 questionnaires per study area (n = 14, SE = 61.3)
Summary
Urbanization is a major cause of land use change worldwide, typically resulting in the loss of biodiversity [1]. The presence of residents lends itself to the use of questionnaire surveys and “citizen science” based approaches which have been used successfully to monitor urban mammals [30, 8] Both foxes and badgers typically live in social groups that defend exclusive territories and seasonally produce one litter per year [31, 13]. Mean territory size was estimated from local radio-tracking and mean group size from capture-mark recapture studies This method was subsequently used in several urban areas to derive data for populating predictive models to determine FGD in multiple cities in Britain [27]. We discuss the method’s wider applicability to other urban carnivores
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