Individual spatial responses towards roads: implications for mortality risk

Temporal and spatial patterns of small vertebrate roadkill in a supercity of eastern China

An assessment of animal roadkill can help develop road mitigation measures. This article is the first to report data on animal-vehicle collisions (AVCs) in Nanjing, a supercity in eastern China. The research was conducted on a 224.27 km stretch of nine roads in Nanjing. In the period, between November 2020 and October 2021, 26 fortnightly monitoring missions were conducted to gather roadkill carcasses so that we could analyze their temporal and spatial distribution patterns. A total of 259 carcasses were collected, comprising 22 different species, of which 46.42% were mammals and 48.81% were birds. Cats and dogs are the most roadkill mammals, and blackbirds and sparrows are the most roadkill birds. The temporal analysis demonstrated that the peak of vertebrate roadkill occurred from May to July. Spatial analysis showed that the distribution patterns of vertebrate roadkill on different roads varied with a generally non-random distribution and aggregation. By mapping accidents using kernel density analysis, we were able to pinpoint locations that were at high risk for roadkill. Due to the fortnightly survey, our results would underestimate the casualties, even if, our study suggests that the problem of car accidents due to animals should be a cause for concern, and the results of the analysis of temporal and spatial patterns contribute to the establishment of mitigation measures.

Demographic effects of road mortality on mammalian populations: a systematic review

In light of rapidly expanding road networks worldwide, there is increasing global awareness of the growing amount of mammalian roadkill. However, the ways in which road mortality affects the population dynamics of different species remains largely unclear. We aimed to categorise the demographic parameters in mammalian populations around the world that are directly or indirectly affected by road mortality, as well as identify the most effective study designs for quantifying population-level consequences of road mortality. We conducted a comprehensive systematic review to synthesise literature published between 2000 and 2021 and out of 11,238 unique studies returned, 83 studies were retained comprising 69 mammalian species and 150 populations. A bias towards research-intensive countries and larger mammals was apparent. Although searches were conducted in five languages, all studies meeting the inclusion criteria were in English. Relatively few studies (13.3%) provided relevant demographic context to roadkill figures, hampering understanding of the impacts on population persistence. We categorised five direct demographic parameters affected by road mortality: sex- and age-biased mortality, the percentage of a population killed on roads per year (values up to 50% were reported), the contribution of roadkill to total mortality rates (up to 80%), and roadkill during inter-patch or long-distance movements. Female-biased mortality may be more prevalent than previously recognised and is likely to be critical to population dynamics. Roadkill was the greatest source of mortality for 28% of studied populations and both additive and compensatory mechanisms to roadkill were found to occur, bringing varied challenges to conservation around roads. In addition, intra-specific population differences in demographic effects of road mortality were common. This highlights that the relative importance of road mortality is likely to be context specific as the road configuration and habitat quality surrounding a population can vary. Road ecology studies that collect data on key life parameters, such as age/stage/sex-specific survival and dispersal success, and that use a combination of methods are critical in understanding long-term impacts. Quantifying the demographic impacts of road mortality is an important yet complex consideration for proactive road management.

Direct and indirect effects of roads on space use by jaguars in Brazil

Roads pose an imminent threat to wildlife directly through mortality and changes in individual behavior, and also indirectly through modification of the amount and configuration of wildlife habitat. However, few studies have addressed how these mechanisms interact to determine species response to roads. We used structural equation modeling to assess direct and indirect effects (via landscape modification) of roads on space use by jaguars in Brazil, using radio-tracking data available from the literature. We fit path models that directly link jaguars' space use to roads and to land cover, and indirectly link jaguars' space use to roads through the same land cover categories. Our findings show that space use by jaguars was not directly affected by roads, but indirect effects occurred through reductions in natural areas on which jaguars depend, and through urban sprawl. Males´ space use, however, was not negatively influenced by urban areas. Since jaguars seem to ignore roads, mitigation should be directed to road fencing and promoting safe crossings. We argue that planners and managers need to much more seriously take into account the deforestation and the unbridled urban expansion from roads to ensure jaguar conservation in Brazil.

Effect of disturbances and habitat fragmentation on an arboreal habitat specialist mammal using GPS telemetry: a case of the red panda

CONTEXT

Habitat specialists residing in human-modified landscapes are likely to be more vulnerable to disturbance because of a functional reliance on very particular habitat features. However, there have been few studies designed to specifically address that issue.

OBJECTIVES

This study aimed to explore how the red panda, an iconic endangered habitat specialist, behaves when faced with disturbances and habitat fragmentation. In particular, we attempted to examine the effect of anthropogenic disturbances and fragmentation on home-range size, activity patterns, and recursion.

METHODS

Using GPS telemetry we monitored 10 red pandas and documented disturbances using camera trapping for one year in eastern Nepal. We performed spatial analysis, analysed activity patterns and evaluated the effect of habitat fragmentation and disturbances on home-range size and residence time using Linear Mixed Models.

RESULTS

Home-range size increased in areas with low availability of forest cover whilst home ranges were smaller in areas with a high road density. Red pandas spent more time in large habitat patches away from roads and cattle stations. Crossing rates suggested that roads acted as a barrier for movement across their habitat. Red pandas also partitioned their activity to minimize interactions with disturbances.

CONCLUSIONS

Red pandas seem to make a trade-off to co-exist in human-dominated landscapes which may have adverse long-term effects on their survival. This indicates that current patterns of habitat fragmentation and forest exploitation may be adversely affecting red panda conservation efforts and that landscape-scale effects should be considered when planning conservation actions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10980-021-01357-w.

Implications for conservation and game management of the roadkill levels of the endemic Iberian hare (Lepus granatensis)

The Iberian hare (Lepus granatensis) is an important small game species endemic to the Iberian Peninsula for which the incidence of roadkill is unknown. We surveyed Iberian hare-vehicle accidents on road networks in southern Spain, focusing on roads that mainly run through favorable habitats for this species: Mediterranean landscapes with plots of arable crops, olive groves, and vineyards. We recorded roadkills over a 5-month period, estimated hare accident densities on roads, and compared these numbers to hare hunting yields in adjoining hunting estates. We also analyzed the spatial patterns of and potential factors influencing hare roadkills. We detected the existence of black spots for hare roadkills in areas with high landscape heterogeneity that also included embankments and nearby crossroads and had high traffic intensity. Hare roadkill levels ranged from 5 to 25% of the annual harvest of hares killed on neighboring hunting estates. We suggest that road collisions should be considered in Iberian hare conservation in addition to hunting, since they may represent an additive source of mortality. Game managers should address the issue of hare roadkill in harvest planning to compensate for hare accidents, adjusting hunting quotas to account for this unnatural source of mortality. Our results suggest future directions for applied research in road ecology, including further work on demographic compensation and roadkill mitigation.

How Is Wildlife Affected by the COVID-19 Pandemic? Lockdown Effect on the Road Mortality of Hedgehogs

Globally, wildlife is affected by unprecedented changes related to the COVID-19 pandemic. In this paper, the lockdown effect on the traffic-related mortality in hedgehogs in an urban area was studied. Comparing the pre-pandemic (2018 and 2019) and pandemic (2020) years, we showed that hedgehog roadkill levels during the lockdown period were over 50% lower (which means a decrease greater than the decrease in road traffic in the same period measured by the number of accidents or the average number of vehicles per day). Based on literature data, we showed that this may mean at least tens of thousands of hedgehogs have survived on a national scale. We report the need to start intensive research on the possible demographic and genetic effects of this unique phenomenon. We also ask how stable the effect of the COVID-19 pandemic will be on wildlife and whether the lockdown (which is an anthropause) may reverse the negative trends in the decline in the number of wild species, including hedgehogs.

Impacts and Potential Mitigation of Road Mortality for Hedgehogs in Europe

Transport infrastructure is a pervasive element in modern landscapes and continues to expand to meet the demands of a growing human population and its associated resource consumption. Road-induced mortality is often thought to be a major contributor to the marked declines of European hedgehog populations. This review synthesizes available evidence on the population-level impacts of road mortality and the threat to population viability for the five hedgehog species in Europe. Local and national studies suggest that road mortality can cause significant depletions in population sizes, predominantly removing adult males. Traffic collisions are a probable cause of fragmentation effects, subsequently undermining ecological processes such as dispersal, as well as the genetic variance and fitness of isolated populations. Further studies are necessary to improve population estimates and explicitly examine the consequences of sex- and age-specific mortality rates. Hedgehogs have been reported to use crossing structures, such as road tunnels, yet evaluations of mitigation measures for population survival probability are largely absent. This highlights the need for robust studies that consider population dynamics and genetics in response to mitigation. In light of ongoing declines of hedgehog populations, it is paramount that applied research is prioritised and integrated into a holistic spatial planning process.

Simulating the Consequences of Roads for Wildlife Population Dynamics

Rapidly expanding road networks have been a key driver of the fragmentation and isolation of many wildlife species, and are a source of significant mortality due to collisions with vehicles. But not all animals are affected equally by transportation infrastructure, and in most cases little is known about the population-scale consequences of roads for wildlife. Even less information is available to characterize species' behavioral responses to roads. Although research shows that maned wolves (Chrysocyon brachyurus) in Brazil are experiencing considerable fragmentation and road mortality, the degree to which these disturbances are impacting the species' viability is unknown. The goal of this study was to analyze the potential effects of roads on maned wolf population size and structure. We used a simulation model to evaluate the population-scale consequences of individual maned wolf interactions with roads, which can result in road crossing, avoidance, or mortality due to a collision with a vehicle. We also forecasted where in Brazil these impacts might be most significant. Our model incorporated species demographic and movement parameters, plus habitat quality and a map of the road network. We found that even moderate rates of road mortality led to severe declines in population size, and that four specific locations accounted for a disproportionate fraction of roadkill events. Our approach will be generally useful for evaluating the relative importance of road effects on species conservation in many ecological systems, for prioritizing data collection efforts, and for informing conservation policies and mitigation strategies.

Factors influencing predator roadkills: The availability of prey in road verges

Road mortality is the most noticeable effect of roads on wildlife. Road verges may provide important refuges for small mammals and rabbits, particularly when roads cross intensive agricultural or grazed areas. In these circumstances, the increasing use of verges by prey species may attract predators to road surroundings increasing the risk of roadkill. The aim of this study was to quantify the role of prey availability (small mammals and rabbits) on predator road casualties, taking into account road and surrounding landscape characteristics. We analyzed this effect on different predator species, such as, snakes, owls and mammal carnivores. The study took place in a 10 km stretch of a National Road (EN4) in southern Portugal. Relationships among predator mortality and explanatory variables (prey abundance, landscape characteristics, and road verge features) were evaluated using Multivariate Redundancy Analysis (RDA) followed by a variation partitioning. Our results show that, although landscape features explained most of the mortality variation, the prey availability was also very important. Roadkills of Montpellier snake and Egyptian mongoose are strongly associated with wild rabbit abundance on verges, while mortality of stone marten, barn owl and tawny owl is related with wood mouse abundance, Mediterranean forest (montado) density, and verge shrub density. Implications for verge management and implementation of mitigation actions are discussed. We suggest vegetation removal in verges to decrease shelter and food availability for prey, and/or the promotion of habitat for prey in areas distant from roads.

Spatial Response to Linear Infrastructures by the Endangered Golden Lion Tamarin

Linear infrastructures are a primary driver of economic development. However, they also can negatively affect wildlife by mortality and the barrier effect. In this paper, we address how paved and unpaved roads, high-tension power lines, and gas/oil pipelines affect home range size, core areas, and movement in an endangered primate, the golden lion tamarin (GLT). Location data were recorded using radio telemetry on 16 groups in two protected areas and in privately owned forest fragments. The GLT’s home range, not core area, increased in size for the groups that occupied locations far from linear infrastructures; home range was also significantly influenced by available forest size. None of the home ranges contained a road, but home ranges did contain power lines. GLTs used the surrounding landscape near all types of infrastructure. Movement analysis showed that most of the step lengths (distances between subsequent locations) were less than 100 m between two consecutive locations, but step length was longer for roads and longer for groups in fully forested habitats. Tamarins avoided paved roads when in close proximity to this type of infrastructure; this behavior increased in areas without adequate adjacent forest habitat. Our results show that linear infrastructures differ in their level of impact: roads can act as a barrier, whereas other types of infrastructure have minimal effect on movement and home range. We discuss these differences in impact in terms of structure, maintenance schedules, and edge effects of infrastructure.

Road effects on bat activity depend on surrounding habitat type

The effects of roads on bats are still a poorly documented issue. Most of the available research focuses on large and high-traffic highways, while low-medium-traffic roads are often assumed to have negligible impacts. However, small roads are ubiquitous in landscapes around the world. We examined the effects of these roads, as well as habitat types, on the activity of three bat guilds (short-, mid- and long-range echolocators) and the most common bat species Pipistrellus kuhlii. We performed three bat acoustic surveys between May and October 2015, with these surveys being performed along twenty transects that were each 1000 m long and perpendicular to three roads with different traffic volumes. The surveys were performed in dense Mediterranean woodland ("montado") and open agricultural field habitats, which were the two dominant land uses. At each transect, bat activity was simultaneously registered at 0, 50, 100, 200, 500 and 1000 m from the road with the use of an ultrasound recorder. According to the generalized linear mixed effects models, the overall activity of bats and of the short- and mid-range echolocators increased with increased distance from the roads and was dependent on the surrounding habitats. In contrast, the long-range echolocators and P. kuhlii were more tolerant to road. Our results also show that the activity was higher in woodland areas, however road verges seem to be a significant habitat in an open agricultural landscape. The major negative effects extended to approximately 300 m from the roads in woodlands and penetrate further into the open field (>500 m). The management of roadside vegetation, combined with the bat habitat improvement in areas that are further from the roads, may mitigate the negative effects. To make road-dominated landscapes safer for bats, the transport agencies need to balance the trade-offs between habitat management and road kill risk.

Wildlife-vehicle collisions in Lanzarote Biosphere Reserve, Canary Islands

Insular wildlife is more prone to extinction than their mainland relatives. Thus, a basic understanding of non-natural mortality sources is the first step in the development of conservation management plans. The Canary Islands are an important tourist destination due to their unique climate and rich scenery and biodiversity. During the last few decades, there has been significant development of urban areas and busy road networks. However, there have been no studies describing the effects of road mortality on wildlife in this archipelago. We describe the temporal and spatial patterns of wildlife roadkill in Lanzarote (UNESCO Biosphere Reserve), using counts from cars for an entire annual cycle. A total of 666 roadkills were recorded (monthly average of 0.09 birds/km and 0.14 mammals/km) comprising at least 37 species including native birds and introduced mammals. Seasonal abundance, richness and diversity of roadkills showed a high peak during summer months for both mammals and birds. GLMs indicated that accidents (including birds and mammals) have a higher probability of occurrence close to houses and on roads with high speed limits. When analysed separately, mammal kills occurred in sectors with high speed limits, close to houses and in areas surrounded by exotic bushes, while bird roadkills appeared in road sectors with high speed limits, close to houses and low traffic volume. Our findings highlight that roads are a potential threat to native birds in the eastern Canary Islands. Detailed studies on the local population dynamics of highly affected species, such as the Houbara Bustard, Eurasian Stone Curlew, Barn Owl or Southern Shrike, are urgently needed to determine whether these levels of road mortality are sustainable.

A new large-scale index (AcED) for assessing traffic noise disturbance on wildlife: stress response in a roe deer (Capreolus capreolus) population

Anthropogenic noise is a growing ubiquitous and pervasive pollutant as well as a recognised stressor that spreads throughout natural ecosystems. However, there is still an urgent need for the assessment of noise impact on natural ecosystems. This article presents a multidisciplinary study which made it possible to isolate noise due to road traffic to evaluate it as a major driver of detrimental effects on wildlife populations. A new indicator has been defined: AcED (the acoustic escape distance) and faecal cortisol metabolites (FCM) were extracted from roe deer faecal samples as a validated indicator of physiological stress in animals moving around in two low-traffic roads that cross a National Park in Spain. Two key findings turned out to be relevant in this study: (i) road identity (i.e. road type defined by traffic volume and average speed) and AcED were the variables that best explained the FCM values observed in roe deer, and (ii) FCM concentration was positively related to increasing traffic volume (road type) and AcED values. Our results suggest that FCM analysis and noise mapping have shown themselves to be useful tools in multidisciplinary approaches and environmental monitoring. Furthermore, our findings aroused the suspicion that low-traffic roads (< 1000 vehicles per day) could be capable of causing higher habitat degradation than has been deemed until now.

Individuals matter: predicting koala road crossing behaviour in south-east Queensland

The ability to predict the frequency with which koalas (Phascolarctos cinereus) cross roads is an important step in developing mitigation strategies aimed at maintaining metapopulation viability for this species. In south-east Queensland, Australia, rapid urban development, including fragmentation and vehicle-related mortality, has contributed to a dramatic decline in local koala populations. Assessment of wildlife crossing structures that mitigates the impact of roads demonstrates these to be beneficial for many species. However, building enough structures to enable animals to move freely across impacted landscapes may be prohibitive in complex urban landscapes. The focus for this study was to consider the role of differing characteristics for species at risk. We examined the frequency of road crossings by individual koalas among six subpopulations in south-east Queensland. We explored the influence of potential predictor variables including: age, sex, and distance from roads. We established that road crossings were limited to a subset of individuals, with only 18 of 51 (~35%) koalas studied ever crossing a road. We found that koalas were disproportionately more likely to cross a road if they had initially been found within a distance of 100 m of that road. Males were more likely to cross roads than females, as were koalas aged less than five years. We suggest that successful wildlife road mitigation can be improved by better understanding the road-crossing behaviour of species such as the koala.

Transport infrastructure shapes foraging habitat in a raptor community

Transport infrastructure elements are widespread and increasing in size and length in many countries, with the subsequent alteration of landscapes and wildlife communities. Nonetheless, their effects on habitat selection by raptors are still poorly understood. In this paper, we analyzed raptors' foraging habitat selection in response to conventional roads and high capacity motorways at the landscape scale, and compared their effects with those of other variables, such as habitat structure, food availability, and presence of potential interspecific competitors. We also analyzed whether the raptors' response towards infrastructure depends on the spatial scale of observation, comparing the attraction or avoidance behavior of the species at the landscape scale with the response of individuals observed in the proximity of the infrastructure. Based on ecological hypotheses for foraging habitat selection, we built generalized linear mixed models, selected the best models according to Akaike Information Criterion and assessed variable importance by Akaike weights. At the community level, the traffic volume was the most relevant variable in the landscape for foraging habitat selection. Abundance, richness, and diversity values reached their maximum at medium traffic volumes and decreased at highest traffic volumes. Individual species showed different degrees of tolerance toward traffic, from higher abundance in areas with high traffic values to avoidance of it. Medium-sized opportunistic raptors increased their abundance near the traffic infrastructures, large scavenger raptors avoided areas with higher traffic values, and other species showed no direct response to traffic but to the presence of prey. Finally, our cross-scale analysis revealed that the effect of transport infrastructures on the behavior of some species might be detectable only at a broad scale. Also, food availability may attract raptor species to risky areas such as motorways.

Inter-individual variability of stone marten behavioral responses to a highway

Efforts to reduce the negative impacts of roads on wildlife may be hindered if individuals within the population vary widely in their responses to roads and mitigation strategies ignore this variability. This knowledge is particularly important for medium-sized carnivores as they are vulnerable to road mortality, while also known to use available road passages (e.g., drainage culverts) for safely crossing highways. Our goal in this study was to assess whether this apparently contradictory pattern of high road-kill numbers associated with a regular use of road passages is attributable to the variation in behavioral responses toward the highway between individuals. We investigated the responses of seven radio-tracked stone martens (Martes foina) to a highway by measuring their utilization distribution, response turning angles and highway crossing patterns. We compared the observed responses to simulated movement parameterized by the observed space use and movement characteristics of each individual, but naïve to the presence of the highway. Our results suggested that martens demonstrate a diversity of responses to the highway, including attraction, indifference, or avoidance. Martens also varied in their highway crossing patterns, with some crossing repeatedly at the same location (often coincident with highway passages). We suspect that the response variability derives from the individual's familiarity of the landscape, including their awareness of highway passage locations. Because of these variable yet potentially attributable responses, we support the use of exclusionary fencing to guide transient (e.g., dispersers) individuals to existing passages to reduce the road-kill risk.

Relative effects of road risk, habitat suitability, and connectivity on wildlife roadkills: the case of tawny owls (Strix aluco)

Background

Despite its importance for reducing wildlife-vehicle collisions, there is still incomplete understanding of factors responsible for high road mortality. In particular, few empirical studies examined the idea that spatial variation in roadkills is influenced by a complex interplay between road-related factors, and species-specific habitat quality and landscape connectivity.

Methodology/Principal Findings

In this study we addressed this issue, using a 7-year dataset of tawny owl (Strix aluco) roadkills recorded along 37 km of road in southern Portugal. We used a multi-species roadkill index as a surrogate of intrinsic road risk, and we used a Maxent distribution model to estimate habitat suitability. Landscape connectivity was estimated from least-cost paths between tawny owl territories, using habitat suitability as a resistance surface. We defined 10 alternative scenarios to compute connectivity, based on variation in potential movement patterns according to territory quality and dispersal distance thresholds. Hierarchical partitioning of a regression model indicated that independent variation in tawny owl roadkills was explained primarily by the roadkill index (70.5%) and, to a much lesser extent, by landscape connectivity (26.2%), while habitat suitability had minor effects (3.3%). Analysis of connectivity scenarios suggested that owl roadkills were primarily related to short range movements (<5 km) between high quality territories. Tawny owl roadkills were spatially autocorrelated, but the introduction of spatial filters in the regression model did not change the type and relative contribution of environmental variables.

Conclusions

Overall, results suggest that road-related factors may have a dominant influence on roadkill patterns, particularly in areas like ours where habitat quality and landscape connectivity are globally high for the study species. Nevertheless, the study supported the view that functional connectivity should be incorporated whenever possible in roadkill models, as it may greatly increase their power to predict the location of roadkill hotspots.