Road traffic may be pushing Britain’s smallest hedgehog populations toward collapse, according to a new study showing that even one or two road deaths each year can have devastating consequences. Researchers found that vehicles killed between 15% and 29% of hedgehogs in the local populations they studied annually, accounting for between 38% and 41% of all recorded deaths. The findings reveal that the impact of road mortality is not evenly distributed: large populations may absorb substantial losses, while small populations can be driven into a rapid decline by only a handful of collisions.
The study was led by conservation scientists at Nottingham Trent University and examined how road deaths affect hedgehog populations over both short and long timescales. Funded by The British Hedgehog Preservation Society and People’s Trust for Endangered Species, the research combined field surveys with population modelling. Rather than simply counting dead animals, the researchers assessed how road mortality interacted with reproduction, survival, population size, sex ratios and the availability of suitable habitat.
Fieldwork focused on four hedgehog populations in villages and towns across Nottinghamshire. The sites were selected to represent different combinations of habitat and road density while remaining broadly comparable. Researchers walked 838 kilometres of survey routes to estimate the number of hedgehogs present and to measure reproductive rates, adult survival and juvenile survival. These data provided the demographic foundation for calculating whether each population was likely to grow, remain stable or decline under different levels of road mortality.
The team also conducted 269 roadkill surveys over an 18-month period, searching for hedgehog carcasses both within and between the study sites. Each road casualty was recorded according to its location, age and sex. Traffic emerged as the leading cause of recorded hedgehog deaths. The surveys also showed that males were killed more often than females, a pattern that may partly reduce the immediate effect on population growth because a single male can potentially mate with several females. However, that apparent buffer does not protect very small populations from demographic instability.
The largest populations in the study experienced the greatest absolute number of traffic deaths, yet they were able to compensate for many of those losses. Higher overall survival and stronger reproductive rates helped replenish their numbers, while the disproportionate death of males meant that female breeding potential was less severely reduced. In population ecology, this is an example of density-dependent resilience: larger populations generally contain more breeding individuals and may be better able to withstand random losses without crossing a critical threshold.
The situation was radically different for populations containing fewer than 15 hedgehogs. In these small groups, even limited road mortality represented a large fraction of the total population. A single death could remove a significant part of the breeding population, and reproduction was not sufficient to replace the losses. Small populations are also especially vulnerable to demographic stochasticity, in which random events such as the death of a breeding female or the failure of a litter have an outsized effect on future numbers.
The researchers used their field measurements to model long-term population persistence under different roadkill scenarios. If approximately half of the hedgehogs in a population were killed on roads each year, the two smallest populations were projected to lose half their numbers within just two years. Under that scenario, both could face local extinction after nine years. The projections do not mean that every population will follow exactly the same trajectory, but they demonstrate how quickly road mortality can become decisive when numbers are already low.
Even populations with more hedgehogs were not immune to sustained losses. The models indicated that an annual mortality rate of 40% could produce a 40% decline in one of the larger populations and a 51% decline in the other over 50 years. These long-term projections are particularly important because a population may appear stable for several breeding seasons before gradual losses become irreversible. Future increases in traffic levels could intensify the pressure, especially where roads divide otherwise suitable habitat.
The findings challenge the assumption that high roadkill rates are always harmful while low rates are relatively unimportant. The researchers argue that the consequences depend on the biological and environmental condition of each population. Strengthening small populations is therefore a priority, but protecting and reconnecting habitat is equally important. Gardens can provide food, nesting places and shelter when areas of wild vegetation are left undisturbed. Small openings measuring 13 by 13 centimetres in fences and walls, often called “Hedgehog Highways,” can allow animals to move between gardens and neighbouring populations without forcing them onto additional roads. These measures will not eliminate collisions, but they could increase population size, improve gene flow and give declining hedgehog communities a better chance of surviving the traffic threat.
Subject of Research: Hedgehog populations and the population-level consequences of road mortality
Article Title: Beyond the Individual: Multisite Population-Level Consequences of Road Mortality on a Declining Mammal
News Publication Date: 28-Jul-2026
Web References: https://doi.org/10.1111/acv.70082
References: Animal Conservation, DOI: 10.1111/acv.70082
Keywords: Hedgehogs, roadkill, road mortality, wildlife conservation, population ecology, local extinction, habitat connectivity, Hedgehog Highways, British wildlife, endangered species
