Abstract Roads are expanding rapidly across biodiverse regions, including global biodiversity hotspots such as the Tropical Andes and the Chocó/Darién. While roads improve connectivity for human populations, they also lead to significant biodiversity loss through habitat fragmentation, wildlife mortality, and population declines. In this study, we update the distribution ranges of eight mammal species by analyzing a comprehensive dataset of 1,326 georeferenced mammal roadkill records compiled through our citizen science initiative REMFA. We identified eight species with new or uncommon distribution records. Six species: Dasyprocta fuliginosa, Hydrochoerus hydrochaeris, Myoprocta pratti, Tamandua tetradactyla, Didelphis marsupialis, and Didelphis pernigra, were recorded at elevations outside their known ranges, representing shifts of up to 1,521 m. Additionally, although our records of Leopardus garleppi and Neogale frenata do not constitute new distributional records, they document occurrences well beyond the species’ historically common ranges in the country, providing further evidence of possible recent range expansions. These findings may reflect either the presence of previously undetected populations or recent range shifts potentially driven by anthropic pressures. Our results highlight the value of roadkill data for biodiversity studies and underscore the need to integrate road ecology into conservation planning. Roadkill observations not only reflect threats to wildlife but can also serve as early indicators of broader ecological changes.

Fleas (Insecta: Siphonaptera) are recognised vectors of bacteria that affect human and other animal health, whose reservoirs are in the majority mammals. Among these, some species of the genera Rickettsia (Rickettsiales: Rickettsiaceae) and Bartonella (Rhizobiales: Bartonellaceae) are emerging and re-emerging throughout the world; however, their circulation across vast regions of Argentina and numerous animal species, particularly wild species remains largely unknown. The study of wild animal roadkill provides valuable insights into parasitic associations and the presence of pathogenic microorganisms, allowing the generation of a health alert in certain ecosystems. The aim of this study was to describe the diversity of fleas associated with roadkilled wild native meso-mammals in the extreme northeast of Argentinian Patagonia, and to detect the presence of Rickettsia and Bartonella bacteria. Five host species were examined, including Chaetophractus villosus Desmarest (Cingulata: Chlamyphoridae); Didelphis albiventris Lund (Didelphimorphia: Didelphidae); Lagostomus maximus Desmarest (Rodentia: Chinchillidae); Leopardus geoffroyi d'Orbigny and Gervais (Carnivora: Felidae) and Lycalopex gymnocercus Fischer (Carnivora: Canidae). A total of 248 fleas were recovered, identified as Hectopsyllidae: Hectopsylla broscus Jordan and Rothschild and Hectopsylla cypha Jordan; Malacopsyllidae: Phthiropsylla agenoris Rothschild and Malacopsylla grossiventris Weyenbergh; Pulicidae: Ctenocephalides felis Bouché and Pulex irritans Linnaeus. Molecular analysis detected two flea-borne pathogenic bacteria: Rickettsia felis (Bouyer et al.), found in C. felis from D. albiventris, and Bartonella rochalimae (Eremeeva et al.), reported here for the first time in Argentina, detected in P. agenoris from C. villosus, and in P. irritans from L. maximus and L. gymnocercus. The results contribute to knowledge of flea diversity in Argentinian Patagonia and provide new information about flea-borne pathogens circulating in the wildlife of this region. Furthermore, this study is the first in Argentina to investigate ectoparasites and their associated bacteria in roadkilled animals, making a pioneering contribution to the field. The interesting findings highlight the importance of implementing and expanding road ecology studies, which could easily be replicated in other regions where information gaps on flea and flea-borne bacteria diversity still exist.

Snakes are significant predators in many ecosystems, but high rates of road mortality threaten to diminish their ecological contributions. Documenting species-specific and demographic patterns of road use is crucial for understanding potential impacts, information that can be leveraged for implementing mitigation measures. I investigated the road ecology of a snake community in the Chihuahuan Desert of southern New Mexico, USA. Nocturnal road-cruising surveys were performed three times per month from April to November 2017 along a 37-km stretch of road, which produced 101 snake encounters of 10 species. On average, 4.2 snakes were encountered per survey with no individuals recaptured, equating to a density of 0.057 snakes per kilometer. Seasonal activity patterns indicated a peak in snake encounters from August through October. Standardized data were combined with opportunistic surveys conducted along the same stretch of road from 2014 to 2016. Overall, road mortality was considerable, with 34% of all snakes found dead-on-road (DOR). Across all species, males and females exhibited similar proportions of DOR while juveniles had a lower DOR rate. The Western Diamondback Rattlesnake (Crotalus atrox) was the most frequently observed species across all surveys (48% of all encounters) and 33% of these observations were found DOR. Models for adult C. atrox revealed that longer body sizes were linked to road mortality, where every 1 cm increase in total length increased the probability of a vehicle collision by almost 10%. Preliminary simulations indicated that directional selection against larger body sizes could reduce the mean size in this population by nearly 12 cm in 50 generations (or about 165 years in this species). Road mortality may have set the stage for evolutionary change in a widespread and ecologically important pitviper. Because roads and vehicle traffic will continue to expand globally, efforts to mitigate road-based effects on snakes are essential to implement before major ecological and evolutionary impacts are felt.

Wildlife vehicle collisions (WVCs) represent a significant threat globally to biodiversity conservation, driver safety and economic resources. This study evaluated the magnitude, spatial-temporal patterns, and influencing factors associated with WVCs within Banke National Park (BaNP), Nepal, to inform effective mitigation planning and biodiversity conservation strategies. Data on WVCs and relevant environmental and anthropogenic variables were collected between April 2015 and March 2024 along a 97.3 km road segment traversing BaNP. The methodological approach integrated field surveys, spatial analyses using kernel density estimation, and statistical modelling to pinpoint collision hotspots and elucidate contributing factors. In total, 488 WVC incidents were documented, predominantly involving mammals (87.52%), followed by reptiles (8.58%) and birds (3.88%). Endangered and vulnerable species, including the golden monitor lizard, leopard cat, and four-horned antelope, were among the recorded fatalities. Spatial analysis identified significant WVC hotspots at Muguwa, Obhari, and Khairi, collectively accounting for over 60% of total incidents. Temporal patterns indicated a seasonal peak during autumn (30%), coinciding with increased post-monsoon dispersal and foraging behaviour. Statistical analyses highlighted that road curvature, proximity to water sources, and surrounding land use significantly influenced collision risk. Specifically, higher WVC odds were associated with curved roads and greater distances from settlements, while straighter road segments and higher forest canopy coverage near roads correlated with reduced risk. This study underscores the pressing need for targeted mitigation measures, such as wildlife crossings, speed reduction zones, and enhanced public awareness initiatives, to reduce WVC occurrences and protect vulnerable wildlife in BaNP. The findings contribute to the existing knowledge regarding road ecology and provide crucial insights for informed conservation interventions within protected areas.

This review synthesizes historical and contemporary research on wildlife–vehicle collisions and roadkill, outlining its evolution from early documentation to modern road ecology. It discusses how early efforts in North America and Europe that quantified animal casualties and developed standardized methodologies formed current studies that use advanced geospatial tools, citizen science, and artificial intelligence to analyze spatiotemporal patterns. We examine key ecological, methodological, and economic impacts of roadkill on wildlife populations and human safety, highlighting the role of road density, vehicle speed, and seasonal factors. The framework presented also underscores a commitment to sustainability by integrating environmental conservation with infrastructural development and socio-economic resilience. The review details various mitigation strategies, from fencing and wildlife crossings to dynamic signage, and evaluates their effectiveness in reducing mortality rates, thereby supporting sustainable development in transportation infrastructure and wildlife management. It also identifies research gaps and outlines future directions, advocating for integrated, multidisciplinary approaches to improve wildlife conservation, infrastructure planning, and public awareness in the context of rapidly expanding road networks.

Abstract Roads are pervasive and ubiquitous landscape features that have substantial and predominantly negative effects on wildlife. Conducting road surveys to count animals that have been struck and killed by vehicles is a common method for estimating the impact of roads on wildlife, especially for species at risk and animals with low road avoidance (i.e., herpetofauna). For road surveys to provide accurate animal mortality data, information about carcass persistence in different environmental contexts and in relation to survey frequency is necessary, but few studies have implemented these data into evaluations of road effects. Using road survey data collected in Ontario, Canada, in 2015 and survival analysis, we quantified anuran carcass (n = 91) persistence and determined the effects of carcass characteristics (size, species, condition), road characteristics (lane position, traffic volume), and environmental characteristics (precipitation, temperature) on carcass persistence on the road. Contrary to previous findings, we found that anuran carcasses persisted on roads longer than expected (5.5 ± 4.4 days, mean ± SD), with some carcasses persisting for up to 30 days. Temperature and precipitation had the greatest influence on the duration of anuran carcass persistence. Carcass condition, (i.e., intact versus partially intact carcasses), species, location on the road, and traffic volume had little to no effect on persistence. We recommend incorporating carcass persistence into road ecology studies, especially in the context of evaluating population‐level impacts of road mortality. Failure to do so could alter estimates of population viability and misinform management decisions.

A framework for large-scale risk assessment of road-related impacts, with application to mustelids

Highways are one of the anthropogenic factors that have the greatest impact on terrestrial biodiversity. Barriers, depletion effects, and roads are the most common locations of wild animal roadkill, leading to biodiversity loss in wild vertebrates. However, the corpses of these animals can be used as opportunistic samples, an excellent source of information on topics such as population dynamics, which is one of the aims of road ecology. Nonetheless, there are only a few studies on injuries in roadkilled wild animals. Between 2018 and 2021, road monitoring was performed around three Federal Conservation Units in Brazil. Twenty-four animals, including birds, reptiles, and mammals, were collected. This study aims to characterize the lesions in wild animals that were roadkilled on roads in the Brazilian semi-arid region using necropsy and quantitative computed tomography (QCT). Also, the bone mineral density was measured using QCT and compared with the number of lesions and body condition score. Four types of bone lesions were found in 13 different bones, with an average of 3.25 lesions per bird and 3.75 lesions per reptile and mammal, with no statistical difference between the means (p > 0.05). Providing a database on the main injuries found in wild animals that are frequently roadkilled serves as an aid to wildlife rescue and rehabilitation professionals who contribute to the conservation of species. In addition, the data on road ecology serves as a basis for the implementation of mitigation measures against wildlife roadkills, also contributing to the conservation of species.

ABSTRACTManagers of protected areas need to balance how they use or preserve their resources, especially regarding ‘road ecology’. This study focuses on Kruger National Park's (KNP) common ungulates’ response to tourist vehicles. We answered the following questions for impala, zebra, giraffe, blue wildebeest, greater kudu and steenbok: What mediates animal flight and flight distance from a vehicle? How much of KNP is affected by roads? Are ungulates using or avoiding roads? We sampled 55.9% of KNP's tourist roads, where we approached animals and determined whether and how far they fled. We georeferenced sightings and estimated the amount of land area along KNP's tourist roads where animals would be expected to flee from vehicles. Of 517 animal sightings, Impala were sighted most (263) and steenbok least (32). Impala had the highest flight propensity (42.6%) and wildebeest lowest (13%). Steenbok were found closest to the road (22.13 m) and wildebeest furthest (77.6 m). Impala had the closest tolerance distance (16.63 m), with zebra furthest (44.74 m). Impala fled the least distance (9.93 m) and zebra fled furthest (24.52 m). Binary logistic regressions (BLRs) showed that all species fled more consistently when closer to the road. The amount of KNP affected by animal flight based on BLRs was largest for zebra (2.32% of the park) and smallest for kudu (0.84%). Impala used the first 10 m of the roadside more than expected and 10–20 m from the road less. KNP's ungulates are habituated to vehicles since flight propensity was low, distribution analysis showed no‐road avoidance, flight distance was short, and animals > 50 m from the road generally do not flee. Given the amount of KNP that is already affected by vehicle traffic, as tourism increases, the land solely devoted to wildlife will necessarily decrease. This study aims to provide information for the best management of roads and traffic in KNP.

Road transport systems kill millions of animals on every inhabited continent each year, and thousands of human lives are lost. Odour repellents (ORE) are a WVC mitigation measure which have been extensively applied across central Europe to prevent or minimise the number of ungulate–vehicle collisions (UVCs). OREs aim to increase the vigilance of ungulates near roads and therefore change their behaviour in areas where vehicle collisions may occur. Despite many scientific papers on the topic of odour repellent effectiveness, a lack of behavioural studies means there is still little understanding of the mechanism of ORE functionality. OREs are applied as an area repellent, so their effectiveness is influenced by multiple factors, and constantly discussed by both academics and the lay public. This paper summarises the state of knowledge about application and effectiveness of odour repellents in road ecology, and suggests research questions to fill information gaps.

Inclusion of road ecology criteria within environmental Impact assessment

Urban road ecology focuses on the reciprocal interactions between urban road construction and the ecological environment, aiming to provide valuable insights into sustainable urban road construction. The study of road ecology has established a comprehensive research framework since the early 20th century, with urban road ecology emerging as its sub-discipline that emphasizes the strategic planning of urban roads and the internal dynamics within urban ecosystems. In order to demonstrate the broader research focus and development prospects of urban road ecology, as well as to explore its distinguishing features compared to traditional road ecology, this study conducted a bibliometric analysis of urban road ecology using CiteSpace software version 6.2.R7 based on the Web of Science (WOS) database for the literature in the last 30 years. The analysis reflected the current state of research in this field across three dimensions: collaborative analysis, co-citation analysis, and keyword analysis. The results of the study revealed a scarcity of key terms and publications between 1993 and 2010, followed by an exponential surge in research activities after 2010. However, both collaborative and keyword analyses indicate a lack of long-term, in-depth research in this area, highlighting the absence of a unified system. On this basis, this paper presents three expectations for future research and briefly discusses the limitations of this study.

Abstract Wildlife‐vehicle collisions can be a significant cause of mortality for animals with ranges that overlap roads. Not all species are equally affected by roads and thus conservation practitioners need empirical data to determine appropriate mitigation measures. However, there is a lack of data on how tropical animals, in particular those on the island of Madagascar, are affected by roads and vehicular mortality. In order to fill in this gap in the literature we investigated the ecological and spatial factors influencing roadkill observations along Route National 4 in Ankarafantsika National Park, Madagascar. We observed 80 cases of roadkill along the highway belonging to at least 13 species, including the first published record of a lemur as roadkill. We also found that the density of roadkill was lower in the area between two speedbumps, suggesting these are an effective measure to mitigate wildlife‐vehicle collisions. These results showcase that even within protected areas of Madagascar animals are at risk of vehicular mortality but mitigation measures are possible. Given the high rates of endemicity coupled with vulnerability to extinction of many Malagasy fauna there is an urgent need for more research on road ecology in Madagascar.

Amphibian and reptile road ecology Roads have complex negative impacts on biodiversity and may threaten the persistence of wildlife populations by acting as barriers to movement or sources of increased and sometimes substantial mortality (e.g., van der Ree et al., 2015; Moore et al., 2023) . Amphibians and reptiles (herpetofauna) are known to be particularly susceptible to negative road impacts (e.g., Beebee, 2013; Andrews et al., 2015) . Many species migrate among habitats to support basic life history requirements and must cross dangerous roads multiple times each year. Additionally, most herpetofauna species are relatively slowmoving and freeze in the presence of oncoming vehicles (Andrews and Gibbons, 2005; Mazerolle et al., 2005) , resulting in an increased risk of mortality for the individual, and increased risks of decline or extirpation for vulnerable populations. Road ecology and mitigation solutions have developed substantially in recent decades. However, progress in knowledge of their effectiveness has been hampered by a lack of postmitigation research focused on individual and population-level responses to passagebarrier systems. Examples of critical knowledge gaps include quantified understandings of the proportions of individuals that successfully cross via passages or changes in population abundance over time (e.g., Soanes et al., 2024) . This Research Topic aimed to increase our understanding of both the effects of roads on amphibians and reptiles and the effectiveness of mitigation structures. We sought research from a diversity of regions, landscapes, and species that addressed meaningful road ecology science questions to help inform conservation. Contributed articles fell into three broad categories: 1) Characterizing road mortality and planning for mitigation; 2) Effects of roads, barriers, and passages on movement behavior; and 3) Design, efficacy, and maintenance of barriers and passages. Road mortality hotspots are commonly used for prioritizing placement of fencing and passages; however, data available and approaches used can vary widely (Paemelaere et al., 2023; Ribeiro et al., 2023) . Shin et al. compared citizen science (CS) roadkill data in the Republic of Korea to standardized published data and found advantages of widely available Frontiers in Ecology and Evolution frontiersin.org 01

Animal behaviour is shaped by the ability to identify risks and profitably balance the levels of risks encountered with the payoffs experienced. Anthropogenic disturbances like roads generate novel risks and opportunities that wildlife must accurately perceive and respond to. Basic concepts in predator-prey ecology are often used to understand responses of animals to roads (e.g. increased vigilance, selection for cover in their vicinity). However, prey often display complex behaviours such as modulating space use given varying risks and rewards, and it is unclear if such dynamic balancing is used by animals in the context of road crossings. We tested whether animals dynamically balance risks and rewards relative to roads using extensive field-based and GPS collar data from elk in Yoho National Park (British Columbia, Canada), where a major highway completely bisects their range during most of the year. We analysed elk behaviour by combining hidden Markov movement models with a step-selection function framework. Rewards were indexed by a dynamic map of available forage biomass, and risks were indexed by road crossings and traffic volumes. We found that elk generally selected intermediate and high forage biomass, and avoided crossing the road. Most of the time, elk modulated their behaviour given varying risks and rewards. When crossing the highway compared with not crossing, elk selected for greater forage biomass and this selection was stronger as the number of highway crossings increased. However, with traffic volume, elk only balanced foraging rewards when they crossed a single time during a travel sequence. Using a road ecology system, we empirically tested an important component of predator-prey ecology-the ability to dynamically modulate behaviour in response to varying levels of risks and rewards. Such a test articulates how decision-making processes that consider the spatiotemporal variation in risks and rewards allow animals to successfully and profitably navigate busy roads. Applying well-developed concepts in predator-prey theory helps understand how animals respond to anthropogenic disturbances and anticipate the adaptive capacity for individuals and populations to adjust to rapidly changing environments.

Abstract Reptiles are an understudied group in road ecology, despite evidence of their high vulnerability to road mortality. Recently, trait‐based models have been demonstrated to be valuable tools for explaining and predicting road mortality risks for birds and mammals. The present study aimed to apply such models to reptiles for the first time. We fitted eight random forest regression models, controlling for different survey design variables, to explain 782 empirical road‐kill rates for Brazilian reptiles and selected the best‐performing model to predict road mortality risks for 572 continental species. The results showed that species that are habitat generalists, omnivorous, viviparous, cathemeral, and have intermediate clutch or litter sizes are at a higher risk of being road‐killed. The relationships for other traits included in our models were uncertain, but our findings suggest that population density and species‐specific behavioural responses to roads and traffic may play an important role in road mortality risks. Geographical location and survey design variables (especially sampling speed and sampling time) were more important in explaining the variance of the empirical road‐kill rates than any of the tested ecological and functional traits. Besides adding evidence of the vulnerability of the Amazon region to vertebrate road‐kills, this study highlights some similarities between the relationships identified here and those found for birds and mammals (such as with body mass and habitat breadth). We also corroborate that trait‐based models are useful tools to aid in conservation efforts but indicate that they can be biased by the methodologies used to collect empirical data. Future road‐kill surveys should therefore use methods specifically designed for reptiles and estimate both observer efficiency and carcass removal rates.

IntroductionDesigns for safe and effective road crossing structures for small animals are typically under-road microtunnels and culverts which have varying levels of effectiveness reported in the scientific literature. Many species, particularly migratory amphibians, may have limited ability to find and use passages if they are too far apart, resulting in substantial barrier effects.MethodsWe designed a novel open elevated passage (elevated road segment: ERS), similar to a low terrestrial bridge, that could theoretically be built to any length based upon species needs and movement characteristics. A 30 m length prototype ERS was installed along a forest road with a history of amphibian road mortality in Sierra National Forest, Fresno County, CA, USA. From 2018 to 2021, we monitored small animal activity under the ERS in relation to surrounding roadside and forest habitats using active infrared cameras.ResultsWe documented a total of 8,815 unique use events, using species specific independence criteria, across 22 species of amphibians (3), reptiles (4), and small mammals (15). Poisson regression modeling of taxonomic group activity under the ERS, roadside and forest, showed that amphibian activity was highest in the forest habitat, no differences were observed for reptiles, and small mammal activity was highest under the ERS. However, mean activity estimates under the ERS were equal to or greater than the open roadside habitat for all 22 species, suggesting that adding cover objects, such as downed logs and vegetation may further enhance passage use.DiscussionOverall, results showed that the design of the ERS crossing has potential to provide high connectivity for a wide range of amphibian, reptile, and small mammal species while reducing road mortality. ERS systems can also be used in areas with challenging terrain and other hydrological and environmental constraints. Incorporating current road ecology science, we provide supplemental ERS concept designs for secondary roads, primary roads and highways to help increase the options available for road mitigation planning for small animals.

The rapidly expanding global road network poses threats to wildlife, including direct mortality. Given limited knowledge and resources, strategic allocation is critical. We introduce a method to identify areas and taxa affected by vehicle collisions as priorities to study and protect. The method is illustrated using Latin America as a case study. In this region high biodiversity and an expanding road network can result in high impacts from roads, yet emerging research expertise offers opportunities for action. To identify priority targets, we combined predicted spatially-explicit roadkill rates for birds and mammals with information about the current road network and species conservation status. Priority areas for conservation (with many species susceptible to roadkill but few or inexistent roads) were largely concentrated in the Amazon, while priority areas for research (unstudied regions with many roads and many species susceptible to roadkill) occur in various areas from Southern Mexico to Chile. Priority taxa for conservation reflected studied, roadkill-susceptible groups (e.g., vultures and armadillos), while priority taxa for research were defined as either poorly-studied roadkill-susceptible groups or unstudied groups of conservation concern (e.g., cuckoos and shrew opossums). Our approach offers a tool that could be applied to other areas and taxa to facilitate a more strategic allocation of resources in conservation and research in road ecology.

Adult mortality is often the most sensitive vital rate affecting at-risk wildlife populations. Therefore, road ecology studies often focus on adult mortality despite the possibility for roads to be hazardous to juvenile individuals during natal dispersal. Failure to quantify concurrent variation in mortality risk and population sensitivity across demographic states can mislead the efforts to understand and mitigate the effects of population threats. To compare relative population impacts from road mortality among demographic classes, we weighted mortality observations by applying reproductive value analysis to quantify expected stage-specific contributions to population growth. We demonstrate this approach for snapping turtles (Chelydra serpentina) observed on roads at two focal sites in Ontario, Canada, where we collected data for both live and dead individuals observed on roads. We estimated reproductive values using stage-classified matrix models to compare relative population-level impacts of adult and juvenile mortality. Reproductive value analysis is a tractable approach to assessing demographically variable effects for applications covering large spatial scales, nondiscrete populations, or where abundance data are lacking. For one site with long-term life-history data, we compared demographic frequency on roads to expected general population frequencies predicted by the matrix model. Our application of reproductive value is sex specific but, as juvenile snapping turtles lack external secondary sex characters, we estimated the sex ratio of road-crossing juveniles after dissecting and sexing carcasses collected on roads at five sites across central Ontario, Canada. Juveniles were more abundant on roads than expected, suggesting a substantial dispersal contribution, and the road-killed juvenile sex ratio approached 1:1. A higher proportion of juveniles were also found dead compared with adults, and cumulative juvenile mortality had similar population-level importance as adult mortality. This suggests that the impact of roads needs to be considered across all life stages, even in wildlife species with slow life histories, such as snapping turtles, that are particularly sensitive to adult mortality.

Where to invest in road mitigation? A comparison of multiscale wildlife data to inform roadway prioritization