Road casualties tell us something about the living
You might think a field guide to identifying ‘roadkill’ was unnecessarily macabre, but as Roger Knutson explains in his 1987 book, Flattened Fauna, ‘in becoming part of the road fauna … an animal loses not only its life but also … most of its mass and much of its normal shape, [but it] has not lost its biological interest.’
This point wasn’t lost on Pat Morris at Royal Holloway, University of London, who was among the first to appreciate counting road casualties can tell us something about the living.
The idea solves two problems. Dr Morris was interested in hedgehogs and how the population across Britain might be changing. But hedgehogs are mostly nocturnal and, while we might encounter one occasionally in a garden on a summer evening, we’re hardly tripping over them. Dedicated researchers can walk miles, night after night, and not see a single one. So, counting them (with any measure of confidence) is tricky.
An alternative tactic is to look for signs, such as droppings, which are more conspicuous during the day (as surveys of otters and water voles do). The problem with this approach, however, is that, while signs indicate an animal’s presence, they don’t necessarily tell you how many animals there are.
Counting road casualties gets around this – one corpse equals one (formerly) alive animal – and is easier than counting something that only comes out at night.
Early pilot surveys
Dr Morris reasoned that if the distance driven was recorded, along with the incidence of dead hedgehogs, then the relative abundance of hedgehogs from year to year could be estimated. In 1988, he piloted the Hedgehog Road Kills Survey with the support of volunteers from the Mammal Society and over the next four years, collected 4,625 records of hedgehog casualties over 214,435 km.
The survey found regional differences in counts, with fewest hedgehogs per kilometre in the South West of England and the highest, in the North East, East Midlands, and East Anglia. Monitoring wild populations by counting road casualties was possible and a few years later, with funding from the Joint Nature Conservation Committee, PTES launched Mammals on Roads, using the Hedgehog Road Kills Survey protocol and with the help of pat Morris’ former student, Paul Bright.
‘Mammals on Roads’ revealed how populations are changing
Since it began, in 2001, Mammals on Roads has played a central part in increasing our knowledge of the impact roads have on wildlife and of how populations of some animals are changing. More than half a million kilometres of roads have been surveyed and close to 100,000 casualties recorded. Perhaps most importantly, Mammals on Roads was one of the first surveys to sound alarm bells for rural populations of hedgehogs. It’s findings have contributed to understanding the scale and distribution of hedgehog road casualties, estimating the number of hedgehogs killed on our roads and identifying roadkill ‘blackspots’. They’ve helped to elucidate the reasons for the decline and contributed to reports such as the State of Britain’s Hedgehogs 2022.
Thank you to everyone who’s taken part. Without their support, it wouldn’t have been possible.
(And special mention must go to the Worthington family who have taken part almost every year since the survey began, sending in records over nearly 25 years – thank you!)
But, while Mammals on Roads has told us a lot, like everything, it has its limitations. Casualty numbers will, to a lesser or greater extent, reflect traffic volume as well as an animal’s abundance, and the number of cars on our roads has steadily increased each year. So, while a decline in the number of casualties (despite increasing traffic) is evidence that there are fewer animals in the wider landscape, it’s not clear whether an increase in casualty numbers is because there are more animals or more cars.
With rural hedgehogs in such trouble, the need for a new, dedicated survey is paramount. After almost a quarter of a century, Mammals on Roads is pulling up to let the National Hedgehog Monitoring Programme (NHMP) take the lead. The NHMP is in the final year of a pilot project, using camera traps to estimate population densities in a range of habitats, with the help of wildlife groups and volunteers across the country. (Watch this space for news of its progress.)
Mammals on Roads though has had a fantastic run. It’s been an extraordinary, collaborative achievement and pivotal in pushing forward hedgehog conservation efforts. It’s collected a huge amount of data (that will be poured over further) and may, perhaps with an oil change and a new set of tires, return in the future.
For now though, Mammals on Roads has reached the end of a long, important journey, fuelled by volunteers, and one that has made a significant difference to conservation.
Header image credit Paul Bunyard