Roadkill scavenging behaviour in an urban environment

Roads can have negative impacts on wildlife through indirect effects such as fragmentation of habitat, or through direct effects such as fatal collisions with vehicles. Wildlife deaths on British roads number in the millions per year, so the resulting carcasses represent a substantial carrion biomass available as food for scavengers. By removing roadkill in urban areas, scavengers perform a valuable ecosystem service, but the rapid removal of these carcasses by scavengers could bias estimates of the impacts of roads on wildlife. In order to evaluate the scale and context of urban roadkill scavenging, we examined: (i) which species scavenge on roadkill in urban areas, (ii) the likelihood of roadkill being removed by scavengers, and (iii) whether spatial and temporal factors (habitat type and time of day) influenced the rate of removal. Camera traps baited with chicken heads as simulated ‘roadkill corpses’ were deployed in six residential and six parkland sites in the city of Cardiff, UK. Seven species were observed removing the roadkill, with corvids being the most common scavengers, responsible for 42% of removals. Of the 120 corpses, 90 (76%) were removed within 12 h. Time of day had a significant effect on the rate of removal, with the number of carcass removals peaking in the first few hours of daylight. Of roadkill placed at 9 am, 62% of carcasses had been removed after only 2 h. Removal of corpses by scavengers could mean that the actual number of road deaths is six times more than that observed during surveys.