Is it possible to monitor mammal population changes from counts of road traffic casualties? An analysis using Bristol's red foxes Vulpes vulpes as an example


*Philip J. Baker. E-mail:


1. Counts of road traffic casualties (RTCs) have been proposed as one potential method of monitoring changes in the abundance of several mammal species in Britain. However, before such schemes are implemented, it is vital that the relationship between animal density and RTCs is verified and quantified. In this paper, we analyse data collected as part of a long-term study of red foxes Vulpes vulpes in Bristol, UK to determine whether RTCs reflected changes in fox numbers.

2. Associations between fox density and RTC counts were examined using data collected from throughout Bristol during 1978–84 (spatial model) and from an intensive longitudinal study in the north-west of the city during 1990–94 (temporal model). For both sets of data, there was a significant relationship between fox density and RTCs; in the case of the temporal model, this was only evident after the data had been manipulated by calculating running means across seasons. These regression models only explained 58% and 43% of the variance observed in the data, respectively.

3. In both analyses, there was a significant difference between the distribution of casualties and the availability of different road types; more foxes were killed on major category roads (e.g. motorways, A-roads). Incorporating the length of each road category in each region in the spatial model improved the variance explained to 81%. This level of precision would be sufficient for a national monitoring programme. However, we were able to minimize or eliminate a number of factors that could potentially confound the use of RTCs for a national monitoring programme; these factors are discussed in detail. At present, we conclude that further investigation into the validity and precision of this technique is required for a range of mammal species before it could be used in a national monitoring programme.