Table 3.

Summary of published findings, as well as gaps in the literature and recommendations for future research as discussed in this review.

Published Findings	Gaps in Understanding as Revealed by This Review	Directions for Future Research as Recommended by This Review
Traffic collisions may cause an annual loss of 3–24% of a local hedgehog population, and 9–30% of a nationwide population [19,46,53,54]. Road mortality is consistently in the top three contributors to total mortality [40,60,61].	The accuracy of current local and total population estimates. Whether populations can compensate for road mortality with increased survival and/or fecundity.	Establishing standardised surveys for improved population estimates. Long-term population studies to evaluate road mortality in the context of population growth.
Hedgehog roadkill is disproportionately clustered in suburban areas and consists predominately of males and adults [28,30,39,68].	Whether carcass detectability and persistence vary between age groups. How road and habitat characteristics influence road mortality risks between demographic groups over time.	Studies into the road crossing behaviour of different demographic groups. Evaluating the consequences of sex- and age-specific road mortality on hedgehog population trends.
Hedgehog populations appear particularly vulnerable to fragmentation effects [30,81]. Hedgehog populations exhibit distinct genetic substructure, often in relation to linear infrastructure [86,90,91].	Whether the hedgehog’s promiscuity and heteropaternal superfecundity can lessen the impacts of isolation on genetic structure.	Establishing isolation effects from roads, such as using inbreeding coefficients or genetic pedigree analysis.
Exclusionary fences alone are not an appropriate mitigation measure for hedgehog road mortality [96]. Hedgehogs infrequently use crossing structures [96,98,101].	The population-level responses to mitigation measures. Whether the use of crossing structures by badgers impacts their efficacy for hedgehogs. Whether traffic-calming methods are an effective and cheaper option for road mitigation.	Quantification of population viability in relation to mitigation using BACI or control/impact studies, such as using roadkill counts, population density and gene flow. Integration of ecological and socioeconomic perspectives on road mitigation and construction.