Eagle visitation rates to carrion in a winter scavenging guild

Understanding the behavioral ecology of species of conservation concern can help to inform better management. During winters 2011 through 2017, we placed camera traps at stations baited with carrion to investigate characteristics of winter scavenging by golden eagles (Aquila chrysaetos) and bald eagles (Haliaeetus leucocephalus) in eastern Washington and Oregon, USA. Our objectives were to better understand exposure risk of individual eagles to lead contaminants and evaluate factors that affect eagle visitation to carrion to inform measures that reduce lead exposure. We studied photo sequences from 108 traps ( = 2,725 ± 306 [SE] images/trap) and used plumage and physical characteristics to track visitation of 183 individual golden eagles and 90 bald eagles at deer (Odocoileus spp.) carrion until it was totally consumed. At least 1 eagle visited 76% of traps ( = 2.5 ± 0.3 unique eagles/trap). On average, an eagle visited a trap 3.4 ± 0.2 times (range = 1–19 visits) over 1.9 ± 0.1 days (range = 1–9 days). We used general linear mixed models to identify influences on number of eagle visits and pooled visit duration. Individual golden eagles visited carrion about 25% more often and 50% longer than bald eagles, and individual juvenile eagles visited carrion more often and longer than immature and adult eagles. On average, an eagle made an additional visit to carrion for every golden eagle that came to the same trap. Eagles spent less time at offal ( = 26.2 ± 6.4 min) than at a whole carcass ( = 92.9 ± 7.5 min), and understory vegetation immediately surrounding carrion was associated with a 30% reduction in visitation time. In the Pacific Northwest during winter, adult and juvenile golden eagles, by virtue of their abundance and visitation to carrion compared to the immature age class and bald eagles of all ages, have the highest potential for exposure to anthropogenic effects from carrion visitation. Concealment of offal piles in vegetation may reduce, but not eliminate, eagle use because of competing scavengers that expose carrion locations. We found no evidence that carrion proximity to nearest known nests, topography, or snow cover affect visitation by eagles. Thus, short of using alternative ammunition to lead, we recommend burial or removal of offal from hunter-killed ungulates. © 2019 The Wildlife Society.     

Predicting Bald Eagle Collision at Wind Energy Facilities

Bald eagles (Haliaeetus leucocephalus) are currently protected in the United States under the Bald and Golden Eagle Protection Act of 1940 and Migratory Bird Treaty Act of 1918. Given these protections and the increasing development of wind energy throughout the United States, it is important for regulators and the wind industry to understand the risk of bald eagle collisions with wind turbines. Prior probability distributions for eagle exposure rates and collision rates have been developed for golden eagles (Aquila chrysaetos) by the United States Fish and Wildlife Service (USFWS). Given similar information has not been available for bald eagles, the current recommendation by the USFWS is to use the prior probability distributions developed using data collected on golden eagles to predict take for bald eagles. But some evidence suggests that bald and golden eagles may be at different risk for collision with wind turbines and the prior probability distributions developed for golden eagles may not be appropriate for bald eagles. We developed prior probability distributions using data collected at MidAmerican Energy Company's operating wind energy facilities in Iowa, USA, from December 2014 to March 2017 for bald eagle exposure rates and collision rates. The prior probability distribution for collision rate developed for bald eagles has a lower mean collision rate and less variability relative to that developed for golden eagles. We determined that the prior probability distributions specific to bald eagles from these operating facilities are a better starting point for predicting take for bald eagles at operating wind energy facilities in an agricultural landscape than those developed for golden eagles. © 2021 The Wildlife Society.     

Modeling climate change impacts on overwintering bald eagles

Bald eagles (Haliaeetus leucocephalus) are recovering from severe population declines, and are exerting pressure on food resources in some areas. Thousands of bald eagles overwinter near Puget Sound, primarily to feed on chum salmon (Oncorhynchus keta) carcasses. We used modeling techniques to examine how anticipated climate changes will affect energetic demands of overwintering bald eagles. We applied a regional downscaling method to two global climate change models to obtain hourly temperature, precipitation, wind, and longwave radiation estimates at the mouths of three Puget Sound tributaries (the Skagit, Hamma Hamma, and Nisqually rivers) in two decades, the 1970s and the 2050s. Climate data were used to drive bald eagle bioenergetics models from December to February for each river, year, and decade. Bald eagle bioenergetics were insensitive to climate change: despite warmer winters in the 2050s, particularly near the Nisqually River, bald eagle food requirements declined only slightly (<1%). However, the warming climate caused salmon carcasses to decompose more rapidly, resulting in 11% to 14% less annual carcass biomass available to eagles in the 2050s. That estimate is likely conservative, as it does not account for decreased availability of carcasses due to anticipated increases in winter stream flow. Future climate-driven declines in winter food availability, coupled with a growing bald eagle population, may force eagles to seek alternate prey in the Puget Sound area or in more remote ecosystems.     

Nonmotorized recreation and motorized recreation in shrub‐steppe habitats affects behavior and reproduction of golden eagles (Aquila chrysaetos)

Different forms of outdoor recreation have different spatiotemporal activity patterns that may have interactive or cumulative effects on wildlife through human disturbance, physical habitat change, or both. In western North America, shrub‐steppe habitats near urban areas are popular sites for motorized recreation and nonmotorized recreation and can provide important habitat for protected species, including golden eagles. Our objective was to determine whether recreation use (i.e., number of recreationists) or recreation features (e.g., trails or campsites) predicted golden eagle territory occupancy, egg‐laying, or the probability a breeding attempt resulted in ≥1 offspring (nest survival). We monitored egg‐laying, hatching and fledging success, eagle behavior, and recreation activity within 23 eagle territories near Boise, Idaho, USA. Territories with more off‐road vehicle (ORV) use were less likely to be occupied than territories with less ORV use (β = ?1.6, 85% CI: ?2.8 to ?0.8). At occupied territories, early season pedestrian use (β = ?1.6, 85% CI: ?3.8 to ?0.2) and other nonmotorized use (β = ?3.6, 85% CI: ?10.7 to ?0.3) reduced the probability of egg‐laying. At territories where eagles laid eggs, short, interval‐specific peaks in ORV use were associated with decreased nest survival (β = ?0.5, 85% CI: ?0.8 to ?0.2). Pedestrians, who often arrived near eagle nests via motorized vehicles, were associated with reduced nest attendance (β = ?11.9, 85% CI: ?19.2 to ?4.5), an important predictor of nest survival. Multiple forms of recreation may have cumulative effects on local populations by reducing occupancy at otherwise suitable territories, decreasing breeding attempts, and causing nesting failure. Seasonal no‐stopping zones for motorized vehicles may be an alternative to trail closures for managing disturbance. This study demonstrates the importance of considering human disturbance across different parts of the annual cycle, particularly where multiple forms of recreation have varying spatiotemporal use patterns that create human–wildlife interactions.     

A Population Estimate for Golden Eagles in the Western United States

ABSTRACT Researchers have suggested golden eagle (Aquila chrysaetos) populations may be declining in portions of their range. However, there are few baseline data describing golden eagle populations across their range in the western United States. We used aerial line transect distance methodology with a double-observer modification to estimate golden eagle population numbers in 4 bird conservation regions of the western United States. We conducted surveys from 16 August to 8 September 2003, after most golden eagles had fledged and before fall migration. The goal of our sampling strategy was to provide >80% power (α = 0.1) to detect an annual rate of total population change >3% per year over a 20-year period. We observed 172 golden eagles across 148 transects and estimated 27,392 golden eagles (90% CI: 21,352-35,140) occurred in the study area during the late summer and early fall of 2003. Following the surveys, we used Monte Carlo simulation to determine the statistical power to detect trends in the golden eagle populations if yearly surveys were continued over a 20-year monitoring period. The simulation indicated the desired power could be achieved under the current methodology and sample size. The methods utilized in this study can be implemented for other raptor species when population estimates that include nonbreeding members of a population are needed. The results of this study can be utilized by professionals to help manage golden eagle populations and to develop conservation strategies.     

Minimising mortality in endangered raptors due to power lines: the importance of spatial aggregation to optimize the application of mitigation measures

Electrocution by power lines is one of the main causes of non-natural mortality in birds of prey. In an area in central Spain, we surveyed 6304 pylons from 333 power lines to determine electrocution rates, environmental and design factors that may influence electrocution and the efficacy of mitigation measures used to minimise electrocution cases. A total of 952 electrocuted raptors, representing 14 different species, were observed. Electrocuted raptors were concentrated in certain areas and the environmental factors associated with increased electrocution events were: greater numbers of prey animals; greater vegetation cover; and shorter distance to roads. The structural elements associated with electrocutions were shorter strings of insulators, one or more phases over the crossarm, cross-shaped design and pylon function. Of the 952 carcasses found, 148 were eagles, including golden eagle (Aquila chrysaetos), Spanish imperial eagle (Aquila adalberti) and Bonelli's eagle (Aquila fasciata). Electrocuted eagles were clustered in smaller areas than other electrocuted raptors. The factors associated with increased eagle electrocution events were: pylons function, shorter strings of insulators, higher slopes surrounding the pylon, and more numerous potential prey animals. Pylons with increased string of insulators had lower raptor electrocution rates than unimproved pylons, although this technique was unsuccessful for eagles. Pylons with cable insulation showed higher electrocution rates than unimproved pylons, both for raptors and eagles, despite this is the most widely used and recommended mitigation measure in several countries. To optimize the application of mitigation measures, our results recommend the substitution of pin-type insulators to suspended ones and elongating the strings of insulators.     

Availability of optimal‐sized prey affects global distribution patterns of the golden eagle Aquila chrysaetos

Climate and landscape change are expected to significantly affect trophic interactions, which will especially harm top predators such as the golden eagle Aquila chrysaetos. Availability of optimal prey is recognized to influence reproductive success of raptors on a regional scale. For the golden eagle, medium‐sized prey species between 0.5 and 5 kg are widely considered to be optimal prey during the breeding season, whereas smaller and larger species are deemed as energetically sub‐optimal. However, knowledge about the effects of optimal prey availability is still scarce on larger scales. To decrease this apparent knowledge gap, we combined biogeographical information on range margins with information about the foraging behaviour and reproductive success of golden eagles from 67 studies spanning the Northern Hemisphere. We hypothesized that availability of optimal prey will affect foraging behaviour and breeding success and, thus, distribution patterns of the golden eagle not only on a local but also on a continental scale. We correlated the diet breadth quantifying foraging generalism, breeding success and proportions of small (< 0.5 kg), medium (0.5–5 kg) and large‐sized (> 5 kg) prey species within the diet with the minimum distance of the examined eagles to the actual species distribution boundary. Closer to the range edge, we observed decreased proportions of medium‐sized prey species and decreasing breeding success of golden eagles. Diet breadth as well as proportions of small and large‐sized prey species increased, however, towards the range edge. Thus, availability of optimal‐sized prey species seems to be a crucial driver of foraging behaviour, breeding success and distribution of golden eagles on a continental scale. However, underlying effects of landscape characteristics and human influence on optimal prey availability has to be investigated in further large‐scale studies to fully understand the major threats facing the golden eagle and possibly other large terrestrial birds of prey.     

Genetic characteristics of endangered Japanese golden eagles (Aquila chrysaetos japonica) based on mitochondrial DNA D-loop sequences and karyotypes

Mitochondrial DNA D-loop sequences (472 bases) for endangered Japanese golden eagles (Aquila chrysaetos japonica) were investigated to evaluate-intrapopulational genetic variations. Among 23 golden eagles, including origin-known eagles caught in the wild and origin-unknown eagles, 10 variable sites were found in the 472 base-sequences. From the nucleotide substitutions, five haplotypes of D-loop sequences were identified, indicating the occurrence of at least three maternal lineages in golden eagles around Japan. Distribution patterns of D-loop haplotypes suggested a wide genetic communication between local populations around Japan prior to a recent habitat fragmentation and a decrease in the population size. In addition, cytogenetic analysis showed that a karyotype specific to the Japanese golden eagle is consistently 2n=62 including eight microchromosomes. Based on mitochondrial DNA and karyotype data, it is likely that golden eagle populations from Japan and the Korean Peninsula together form a common conservation unit. These results provide an important framework for conservation actions for Japanese golden eagle populations in zoos, and in situ reintroduction and translocation programs. Zoo Biol 17:111–121, 1998. © 1998 Wiley-Liss, Inc.     

Spatio-temporal segregation of facultative avian scavengers at ungulate carcasses

Spatial and/or temporal segregation of resource use are mechanisms that may allow coexistence between potential competitors. Spatial and temporal patterns of carrion use were studied in the main avian scavengers of Sierra Espuña Natural Park (SE, Spain). We monitored the use of ungulate carcasses provided by hunting during winter and summer of 2005–2006. Non-breeding ravens exploited aggregated carcasses and depleted the resource in a few days while golden eagles used scattered carcasses over a longer consumption period. Moreover, non-breeding ravens exploited carcasses when golden eagles were less active. Almost all available hunter kills were exploited by golden eagles and/or ravens during winter whereas a high number of carcasses were not used during the breeding season, suggesting strong competition in a period of low food availability. Thus carrion arrangement, seasonal behaviour and competitive interactions could be affecting the foraging patterns of these two species. Interestingly, intraspecific aggregation of the smaller species and dominance of the larger one may act on the use of shared resources and trigger segregation mechanisms. Our results support that differences in the spatial and temporal patterns of resource use may allow resource partitioning between two species, thus facilitating their coexistence in sympatric areas.     

Widespread Lead Exposure in Golden Eagles Captured in Montana

Lead poisoning threatens many species of raptors, including golden eagles (Aquila chrysaetos). Much of this lead likely comes from bullet fragments that remain in the carcasses of animals killed by hunters. The likelihood of lead exposure may peak during fall hunting seasons and early winter until carcasses from hunting become scarce. From 2011 to 2018 in western Montana, USA, we captured 91 golden eagles in winter, tested their blood lead levels (BLL), and outfitted a subset of birds (n = 29) with global positioning system [GPS] transmitters. Nearly all golden eagles (94.5%) had elevated BLL (≥10 μg/dL), and 8 of them had BLL above clinical exposure (>60 μg/dL), where they may lose coordination and experience a host of other neurological and physiological disorders. Golden eagles caught late in winter tended to have lower BLL than those caught earlier. At least 69% of the golden eagles equipped with GPS transmitters migrated northward, spending the summer throughout Alaska, USA, and northwestern Canada. Blood lead levels did not differ between migratory and nonmigratory golden eagles. Overall, elevated BLL are widespread among golden eagles throughout winter in western Montana. Promoting nonlead hunting ammunition in areas with high densities of golden eagles will reduce the birds' lead exposure. © 2020 The Wildlife Society.     

Bottom‐up processes drive reproductive success in an apex predator

One of the central goals of the field of population ecology is to identify the drivers of population dynamics, particularly in the context of predator–prey relationships. Understanding the relative role of top‐down versus bottom‐up drivers is of particular interest in understanding ecosystem dynamics. Our goal was to explore predator–prey relationships in a boreal ecosystem in interior Alaska through the use of multispecies long‐term monitoring data. We used 29 years of field data and a dynamic multistate site occupancy modeling approach to explore the trophic relationships between an apex predator, the golden eagle, and cyclic populations of the two primary prey species available to eagles early in the breeding season, snowshoe hare and willow ptarmigan. We found that golden eagle reproductive success was reliant on prey numbers, but also responded prior to changes in the phase of the snowshoe hare population cycle and failed to respond to variation in hare cycle amplitude. There was no lagged response to ptarmigan populations, and ptarmigan populations recovered quickly from the low phase. Together, these results suggested that eagle reproduction is largely driven by bottom‐up processes, with little evidence of top‐down control of either ptarmigan or hare populations. Although the relationship between golden eagle reproductive success and prey abundance had been previously established, here we established prey populations are likely driving eagle dynamics through bottom‐up processes. The key to this insight was our focus on golden eagle reproductive parameters rather than overall abundance. Although our inference is limited to the golden eagle–hare–ptarmigan relationships we studied, our results suggest caution in interpreting predator–prey abundance patterns among other species as strong evidence for top‐down control.     

Avian top predator and the landscape of fear: responses of mammalian mesopredators to risk imposed by the golden eagle

Top predators may induce extensive cascading effects on lower trophic levels, for example, through intraguild predation (IGP). The impacts of both mammalian and avian top predators on species of the same class have been extensively studied, but the effects of the latter upon mammalian mesopredators are not yet as well known. We examined the impact of the predation risk imposed by a large avian predator, the golden eagle (Aquila chrysaetos, L.), on its potential mammalian mesopredator prey, the red fox (Vulpes vulpes, L.), and the pine marten (Martes martes, L.). The study combined 23 years of countrywide data from nesting records of eagles and wildlife track counts of mesopredators in Finland, northern Europe. The predation risk of the golden eagle was modeled as a function of territory density, density of fledglings produced, and distance to nearest active eagle territory, with the expectation that a high predation risk would reduce the abundances of smaller sized pine martens in particular. Red foxes appeared not to suffer from eagle predation, being in fact most numerous close to eagle nests and in areas with more eagle territories. This is likely due to similar prey preferences of the two predators and the larger size of foxes enabling them to escape eagle predation risk. Somewhat contrary to our prediction, the abundance of pine martens increased from low to intermediate territory density and at close proximity to eagle nests, possibly because of similar habitat preferences of martens and eagles. We found a slightly decreasing trend of marten abundance at high territory density, which could indicate that the response in marten populations is dependent on eagle density. However, more research is needed to better establish whether mesopredators are intimidated or predated by golden eagles, and whether such effects could in turn cascade to lower trophic levels, benefitting herbivorous species.     

Carcass permanency time and its implications to the roadkill data

Roadkill studies are typically conducted without regard to the carcass permanency time on the highway, which may lead to underestimation of roadkill data, especially small animals that are quickly removed by scavengers. To evaluate the carcass duration time on the lane and its relation to the roadkill time event, we conducted an experiment comparing the removal rate of small carcasses between different stretches of a highway and stretches of dirt roads. The rates found in the study were considered high, with 89 % of carcasses being removed in the first 24 h and 66 % within 12 h. The removals were high for both road categories but reached their peaks at different periods of the day, being higher during the day on the highway and at night on dirt roads. We believe that removal on the highway is dictated by higher vehicular traffic and mainly by the action of scavenger birds during the day, while on dirt roads, it is due to the action of different opportunistic scavengers during the night.     

Sources of Mortality in Bald Eagles in Michigan, 1986–2017

As bald eagle populations recover, defining major sources of mortality provides managers important information to develop management plans and mitigation efforts. We obtained data from necropsies on 1,490 dead bald eagles (Haliaeetus leucocephalus) collected in Michigan, USA, conducted from 1986 to 2017 to determine causes of death (COD). Trauma and poisoning were the most common primary COD categories, followed by disease. Within trauma and poisoning, vehicular trauma (n = 532) and lead poisoning (n = 176) were the leading COD subcategories, respectively. Females comprised a greater number of carcasses for most COD diagnoses. The proportion of trauma and poisoning CODs significantly increased in the last few years of the study in comparison to a select few years at the beginning. Trauma CODs were greater in autumn months during whitetail deer (Odocoileus virginianus) breeding and hunting seasons and in February, when aquatic foraging is unavailable and eagles are likely forced to scavenge along roadsides. Poisoning CODs were greatest in late winter and early spring months, when deer carcasses containing lead ammunition, which are preserved by the cold weather, also become a supplemental food source. The major infectious disease CODs, West Nile virus and botulism (Clostridium botulinum type E), were more prevalent during summer months. We recommend moving road-killed carcasses, especially white-tailed deer, from the main thoroughfare to the back of the right-of-way, and the transition from lead ammunition and fishing tackle to non-toxic alternatives to decrease these main anthropogenic sources of mortality for bald eagles, and other scavenger species. © 2020 The Wildlife Society.     

Density-dependence in the survival and reproduction of Bald Eagles: Linkages to Chum Salmon

During the late 20th Century, due to decreases in both contamination and persecution, bald eagle (Haliaeetus leucocephalus) populations increased dramatically. Currently, mechanisms regulating eagle populations are not well understood. To examine potential regulating processes in the Pacific Northwest, where eagles are no longer primarily regulated by contaminants or direct persecution, we examined bald eagle reproductive success, breeding populations, winter populations, mortality, and salmon stream use. Wintering and breeding eagle populations in south-coastal British Columbia (BC) quadrupled between the early 1980s and the late 1990s, and have since stabilized. Density-dependent declines in reproduction occurred during 1986–2009, but not through changes in site quality. Mid-winter survival was crucial as most mortality occurred then, and models showed that density-dependent reductions in population growth rates were partially due to reduced survival. Wintering eagles in British Columbia fed heavily on chum salmon (Oncorhynchus keta) runs, and then switched to birds in late winter, when mortality was highest. Eagles tended to arrive after the peak in salmon availability at streams in BC as part of a migration associated with salmon streams from Alaska to northern Washington. Eagles were most abundant in southern BC during cold Alaskan winters and in years of high chum salmon availability. We suggest that eagle populations in the Pacific Northwest are currently partially limited by density on the breeding grounds and partially by adult mortality in late winter, likely due to reduced late winter salmon stocks forcing eagles to exploit more marginal prey supplies. Larger eagle populations have affected some local prey populations. © 2011 The Wildlife Society.     

Lead poisoning and heavy metal exposure of golden eagles ( Aquila chrysaetos ) from the European Alps

Lead poisoning and organ levels of the non-essential heavy metals lead, cadmium and mercury of seven free-ranging golden eagles (Aquila chrysaetos) from the European Alps, and of one 23-year-old captive golden eagle are reported. All birds were found dead or moribund during the years 2000 and 2001 in Austria, Germany and Switzerland. One golden eagle from Switzerland with extraordinarily high lead residues in its liver and kidney was clearly identified as lethally lead poisoned. Another bird from the same region was found still alive and died in a wildlife rehabilitation center, showing lead residues in its organs known for acute lead poisoning with detrimental physiological effects, such as nervous disorders and the inhibition of the hemoglobine synthesis. Concentrations of cadmium, mercury and lead residues in the organs of the other five free-ranging birds, and in the long-lived captive golden eagle, were low and represent the natural background levels in birds of prey of the terrestrial food web. This is the first published report of lead poisoning in golden eagles from Switzerland. Sources for lead poisoning in golden eagles in the Alpine region are discussed.     

Inter- and intra-specific dominance relationships and feeding behaviour of Golden Eagles Aquila chrysaetos and Sea Eagles Haliatetus albicilla at carcasses

The behaviour of Golden Eagles Aquila chrysaetos and Sea Eagles Haliceetus albicilla scavenging on artificially laid out carcasses in coastal Sør-Trøndelag Province, Norway, was studied during two winters (totalling 640 h of observations) and the intervening summer (430 h). Neither species fed at carcasses in summer. Although smaller, Golden Eagles were strongly dominant over Sea Eagles in direct competition for carcass access. In Sea Eagles, females dominated males, while in Golden Eagles, few conflicts between birds of known sex were observed. Age effects were weak and not statistically significant in both species. Conflicts for carcass access tended to be most escalated between Golden Eagles and least escalated between Sea Eagles, with interspecific conflicts intermediate. Most conflicts were won by the aggressor, suggesting that birds were generally able to assess relative dominance before launching an attack. Young eagles fed longer at a carcass than older individuals in both species, suggesting that young eagles may have been hungrier or less efficient feeders. Sea Eagles waited longer than Golden Eagles between arrival in the immediate carcass area and feeding at the carcass. This effect was greater when the carcass was already occupied but also occurred when no other eagle was already present. While interspecific competition for carrion did not appear to have important consequences for the two species in coastal Norway, in western Scotland, where Sea Eagles are currently re-establishing, carrion is important in the diet of both species all year round. Interspecific competition for this resource may therefore play a role in determining the ultimate realized niche (and therefore numbers) of the two species in Scotland in the longer term.     

Landscapes for Energy and Wildlife: Conservation Prioritization for Golden Eagles across Large Spatial Scales

Proactive conservation planning for species requires the identification of important spatial attributes across ecologically relevant scales in a model-based framework. However, it is often difficult to develop predictive models, as the explanatory data required for model development across regional management scales is rarely available. Golden eagles are a large-ranging predator of conservation concern in the United States that may be negatively affected by wind energy development. Thus, identifying landscapes least likely to pose conflict between eagles and wind development via shared space prior to development will be critical for conserving populations in the face of imposing development. We used publically available data on golden eagle nests to generate predictive models of golden eagle nesting sites in Wyoming, USA, using a suite of environmental and anthropogenic variables. By overlaying predictive models of golden eagle nesting habitat with wind energy resource maps, we highlight areas of potential conflict among eagle nesting habitat and wind development. However, our results suggest that wind potential and the relative probability of golden eagle nesting are not necessarily spatially correlated. Indeed, the majority of our sample frame includes areas with disparate predictions between suitable nesting habitat and potential for developing wind energy resources. Map predictions cannot replace on-the-ground monitoring for potential risk of wind turbines on wildlife populations, though they provide industry and managers a useful framework to first assess potential development.     

Road mortality of pond-breeding amphibians during spring migrations in the Mazurian Lakeland, NE Poland

The effects of road traffic mortality on amphibian populations are in many cases hard to estimate and speculate, primarily due to the inaccuracy of the methods employed in studies. We have analyzed amphibian road mortality during two breeding seasons on selected road sections adjoining spawning ponds and have critically reviewed methods used for estimating the impact of road traffic on migrating amphibians. The mortality rates of particular amphibian species differed significantly and varied according to year, site, and traffic volume. The highest mortality was recorded for Bufo bufo and the lowest for Lissotriton vulgaris. Species-specific parameter estimates of mortality, evaluated on a daily basis counts of roadkills, were positively correlated with the mean body mass of the amphibian species. The share of a given species among carcasses found on the road, commonly used in such studies, proved to be an unreliable measure of mortality. We found that nearly 60% of amphibian roadkill victims had disappeared within 24?h of exposure, and the number of missing carcasses was inversely related to body mass.     

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.