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Application of GIS to a Baseline Survey of Vertebrate Roadkills in Baldwin County, Georgia
Evan R. Boitet and Alfred J. Mead

Southeastern Naturalist, Volume 13, Issue 1 (2014): 176–190

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Southeastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 176 2014 SOUTHEASTERN NATURALIST 13(1):176–190 Application of GIS to a Baseline Survey of Vertebrate Roadkills in Baldwin County, Georgia Evan R. Boitet1,2 and Alfred J. Mead1,* Abstract - Physical attributes, traffic volume, and landscape patterns on a particular road are expected to influence the frequency of vertebrate road fatalities. In this study, we surveyed 22.17 km of roadways in Baldwin County, GA, 171 times (3791.1 km total) for vertebrate roadkills over a calendar year. We coded the survey route—consisting of portions of US Highway 441, GA Highway 212, and Meriwether/Lowe Road—for differing habitat types and obstacles along its length, and mapped the spatial data in ArcGIS. We recorded 178 vertebrate roadkills representing 19 species, primarily mammals, with Odocoileus virginianus (White-tailed Deer; n = 46) and Didelphis virginiana (Virginia Opossum; n = 39) most frequently observed. We calculated a roadkill rate of 8.03/km/yr. US 441, which has the most lanes, highest traffic volume, and greatest verge width, had the highest roadkill rate (10.95/km/yr) of the three sections. Seasonal differences in roadkill frequencies for the most commonly observed species appear to be related to periods of ma ting or dispersal. Introduction The continuing growth and expansion of human populations exerts pressures on wildlife due in part to habitat fragmentation (Watts et al. 2007). An impact of particular concern is wildlife-vehicle collisions, which often result in increased death rates for many wildlife species as well as possible injury and monetary loss for drivers (Conover et al. 1995, Trombulak and Frissell 2000). In 1987, an estimated 1 million vertebrates were killed on roadways in the United States each day (Lalo 1987), and this number has surely risen as human population densities and the numbers of cars on roads have increased (Barthelmess and Brooks 2010). While road mortality may not severely limit species with naturally high population numbers and reproductive rates, populations of threatened or endangered species can be severely impacted (Forman and Alexander 1998, Glista et al. 2008). Local populations may be more sensitive to increased road mortality, especially when roadkill rates exceed the rates of reproduction or immigration (Evink et al. 1996, Forman 1995, Forman and Alexander 1998, Forman et al. 1997). In addition to roadkills, roads can fragment populations thereby reducing dispersal success and gene flow (Conard and Gipson 2006, Maehr et al. 1991, Trombulak and Frissell 2000). Analysis of roadkill rates at the local level provides a more accurate understanding of the effects of human expansion in particular regions and illuminates many factors associated with vertebrate road mortality. 1Department of Biological and Environmental Sciences, CBX 081, Georgia College and State University, Milledgeville, GA 31061. 2Current address - Department of Genetics, Box 2182, University of Alabama at Birmingham, Birmingham, AL 35294. *Corresponding author - al.mead@gcsu.edu. Manuscript Editor: Scott Markwith Southeastern Naturalist 177 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 The frequency of wildlife-vehicle collisions is influenced by species-specific and species-general factors (Coffin 2007, Collins and Kays 2011, Glista et al. 2008) as well as road characteristics such as width (number of lanes), speed limit, traffic volume, verge width (shoulder or right-of-way), and physical barriers present along the roadway (Forman and Alexander 1998, Inbar and Mayer 1999). Animals may be attracted to the verge along roads due to an edge effect and food availability (Coffin 2007). Medium-sized mammals such as Didelphis virginiana (Virginia Opossum) likely are attracted to roadways by the presence of carrion, and Sylvilagus floridanus (Cottontail Rabbit) are attracted by green sprouts following mowing (Forman and Alexander 1998). In addition, wider verge may provide more attractive grazing areas for larger herbivores, such as Odocoileus virginianus (White-tailed Deer). Recently, analyses of the factors influencing wildlife-vehicle collisions have focused on species-specific road mortality by classifying spatial patterns adjacent to roadways and utilizing a geographic information system (GIS) to interpret the data (Clevenger et al. 2001, Slater 2002). GIS analyses have illustrated the relationships of land cover and roadside obstacles (fences, guardrails, water, etc.) with areas of high vertebrate road mortality (Forman and Alexander 1998, Glista et al. 2008), indicating that obstacles along the verge of roadways may funnel species around obstructions and create roadkill hotspots (Ramp et al. 2005). Further identification of spatial patterns that influence wildlife-vehicle collisions will increase our understanding of where these hotspots may occur. Roadkill studies conducted throughout Canada and the US have focused mainly on mammalian roadkills (Alexander et al. 2005, Barthelmess and Brooks 2010, Caro et al. 2000, Clevenger et al. 2003, Conard and Gipson 2006, Forman and Alexander 1998, Gehrt 2002, Kanda et al. 2006), although some studies addressing amphibian roadkills have been published in recent years (Glista et al. 2008, Langen et al. 2007). Within the southeastern US, most studies have documented roadkills along roads in Florida (Cristoffer 1991, Inbar and Mayer 1999, Loughry and Mc- Donough 1996, Main and Allen 2002, Smith and Dodd 2003). The only published study of roadkills in Georgia is a state highway mortality report prepared by the Georgia Game and Fish Division (Johnson 1986). The present study examined vertebrate roadkills in Baldwin County, GA, by conducting surveys on three roads of comparable length but differing road width, traffic volume, and verge width. The research objectives were to (1) determine which species are most commonly detected as roadkill, (2) investigate seasonal effects on the occurrence of the most commonly detected roadkilled species, and (3) compare the distribution of detected roadkills in relation to the number of lanes/traffic volume, land cover, and roadside obstacles utilizing GIS. Methods Baldwin County encompasses 694.1 km2 in central Georgia and has approximately 44,500 residents, of which approximately 17,500 reside within Milledgeville (2011 US Census). The roadkill survey route (Fig. 1) was driven by a single observSoutheastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 178 Figure 1. Location of roads travelled and distribution of the 178 roadkills (black squares) recorded in the 2011 Baldwin County, GA, roadkill survey. A = US Highway 441, B = GA Highway 212, C = Meriwether Road, D = Lowe Road, M = city of Milledgeville. Raster image obtained from Georgia GIS Data Clearinghouse (US Department of Commerce 2005). Data projected in ArcMAP to NAD 83 UTM Zone 17N. Southeastern Naturalist 179 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 er at speeds less than, if possible, or equal to the posted speed limit (Table 1) during daylight morning hours (prior to noon). We surveyed each section of the route in succession three times per week (typically Monday, Wednesday, Friday) from 5 January 2011 to 5 January 2012. We traveled the route each day of one week four times during the observation period (once each season) in order to determine the length of time roadkilled specimens typically remained on the roadway. We drove the 22.17-km survey route 171 times, and recorded all roadkilled mammals, birds, and reptiles visible (on asphalt and in the verge) from the moving survey vehicle. For each roadkilled specimen, we recorded the species, date, and UTM coordinate using a Garmin Dakota 20 GPS. We counted all roadkills only once, even if they remained on the roadway for the succeeding survey trip. For purposes of analysis, we divided the observation period into winter (December–February), spring (March–May), summer (June–August), and fall (September–November). We carried out seasonal analyses for species that were recorded 10 or more times during the year. We caculated roadkill rates (for all species and mammals only), expressed as roadkills/km/yr (RKY), for each section of the survey route, each land-cover class, and each obstacle class by dividing the number of detected roadkills in a section or class for the year by the length of road in that section or class. The selected survey route represented a mixture of road sizes and spatial conditions (Fig. 1, Table 1). We chose cach of the three sections based on length (e.g., all roads were within ± 0.97 km in length) and connectivity. One section combined two intersecting, similarly classified roads (Meriwether/Lowe Road). We obtained the most recent annual average daily traffic (AADT) data for each section from the Georgia Department of Transportation (Table 1; STARS 2010). We determined the average verge width for each section using a metric tape. The survey route consisted of portions of US Highway 441, GA Highway 212, and Meriwether/Lowe Road (Fig. 1). The US 441 section (Fig. 1: label A) is a major 5-lane highway mostly within the Milledgeville city limits and traverses a variety of land-cover types and roadside obstacles. US 441 crosses Tobler Creek, Nancy Branch Creek, and one seasonal stream, and at one point borders a small, 1–2-acre wetland. The GA 212 segment (Fig. 1: label B) is a two-lane highway in a more rural part of the county. Forests dominate the landscape around this route section, but there are a few residential Table 1. Characteristics of roads surveyed in the three sections of the 22.17-km roadkill survey route in Baldwin County, GA. Meriwether (4.92 km) and Lowe (1.91 km) roads were combined (Me- Lo Rd.) to make a 6.83-km section with a combined roadkill rate. The average annual daily traffic (AADT) was obtained from the Georgia Department of Transportation (STARS 2010). Roadkill rates were determined for all species and mammals only. # traffic Speed limit AADT Verge Roadkills (/km/yr) Road name Length (km) lanes (km/hr) (vehicles/yr) width (m) Total Mammals US Hwy 441 7.58 5 72.4–88.5 16,900 8.68 10.95A 10.42 GA Hwy 212 7.76 2 88.5 4040 6.39 6.19 5.67 Me-Lo Rd. 6.83 2 72.4 1820 3.26 6.89 6.30 ASignificant difference (α = 0.05) between US 441 and GA 212 and Me-Lo Rd. Southeastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 180 areas. This portion of GA 212 mostly follows a dry ridge, yet crosses three seasonal streams, and parallels a spur of the Southern Railway along the middle one-third of the route. The combined Meriwether/Lowe Road section consists of two lanes running east–west between US 441 and GA 212. Meriwether Road (Fig. 1: label C) crosses one seasonal creek and private residences line most of its length. Lowe Road (Fig. 1: label D) is bordered by forests as well as private residences, crosses a small beaver pond on Buck Creek, and crosses one seasonal stream. We compiled a geodatabase of the survey route in ArcGIS 10 (ESRI). We coded the sampled roads for spatial analysis using collected GPS data as well as Baldwin County road shapefiles obtained from the Georgia GIS Data Clearinghouse (US Department of Commerce 2005). We divided the survey route into 173 segments of ≥30 m determined by the spatial pattern along the roadway. Attributes were assigned to each segment according to the land cover and obstacles along the verge. Land-cover classes included field, forest, residential, and mixed (differing habitats on either side of the road). Obstacle classes included absent, fence, and mixed. We projected the GPS location for each roadkill in ArcMap allowing for the correlation of the roadkill locations with the spatial surroundings. All GPS coordinates were projected in ArcMAP to NAD 83 UTM Zone 17N. We determined significant differences between the roadkill rates (overall and individually for the 5 most commonly observed species) for each road, season, land-cover type, and obstacle class using a rate-difference analysis by calculating a 95% confidence interval for difference (Sahai and Khurshid 1996). If the confidence interval for the difference included zero, we concluded that the roadkill rates did not differ significantly at α = 0.05. We consider the roadkill totals for the survey route to be conservative based on a number of factors. First, visibility during sampling was limited on some days due to rain, sun, fog, or high traffic volume. Second, travelling over hills and around curves inhibited the single surveyor’s field of view. Third, animals may have been removed from the road either by Georgia Department of Transportation workers, civilians (especially pets in residential areas), or scavengers. Fourth, smaller vertebrates, if not located on the asphalt, were difficult to detect from a moving survey vehicle. Fifth, the verge-mowing regime changed the height of the roadside vegetation at different times during the year, altering visibility. Sixth, since the route was surveyed in the morning, nocturnal species (nighttime and early morning kills) were more likely to be observed than diurnal species (daytime kills). Lastly, some fatal wildlife- vehicle collisions do not result in an animal dead on the road; some animals may not perish until they have fled the roadway and verge. On occasion, scavengers such as Cathartes aura (Turkey Vulture), Coragyps atratus (Bechstein) (Black Vulture), and Corvus brachyrhyncos (American Crow) would be on a carcass while the survey route was driven, increasing the likelihood of detection, even when the roadkill was displaced from the roadway. Results From 5 January 2011 to 5 January 2012, we conducted 171 surveys for a total of 3791.1 km traveled, and recorded 178 roadkills representing 19 species for an Southeastern Naturalist 181 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 average of 8.03 RKY (Table 2). Mammals accounted for 95% of all detected roadkills (167/178), and the five most commonly encountered species, White-tail Deer (n = 46), Virginia Opossum (n = 39), Sciurus carolinensis (Eastern Gray Squirrel; n = 28), Dasypus novemcinctus (Nine-banned Armadillo; n = 22), and Procyon lotor (Northern Raccoon; n = 11), accounted for 87% of the roadkilled mammals (146/167). Turkey Vultures (n = 4) were the most commonly recorded bird. No reptilian species was recorded more than once. Significantly more roadkill (α = 0.05) were detected on US 441 compared to GA 212 and Meriwether/Lowe Road (Table 1). On US 441, 79 mammals, 2 birds, and 2 reptiles were recorded (n = 83, 10.95 RKY). US 441 has the most lanes, highest average annual daily traffic estimate, and greatest verge width. Additional significant differences (α = 0.05) among road transects included more Opossums detected on US 441 compared to Meriwether/Lowe Road, more Armadillos found on US 441 compared to GA 212 and Meriwether/Lowe Road, and more Raccoons recorded on US 441 compared to GA 212 (Table 2). For GA 212, we found 44 mammals and 4 birds, but no reptiles, dead (n = 48, 6.19 RKY). Observations on Meriwether/Lowe Road recorded 43 mammals, 3 birds, and 1 reptile dead (n = 47, 6.89 RKY). This section has the narrowest verge width and the lowest posted speed limit (72.4 km/ hr [45 mph]) along its entire length. Table 2. Vertebrate taxa recorded along the roadkill survey route in Baldwin County, GA. The Meriwether/ Lowe Road section is abbreviated Me-Lo Rd. US Hwy GA Hwy Me-Lo Species Common name 441 212 Rd. Total Odocoileus virginianus (Zimmermann) White-tailed Deer 18 14 14 46 Didelphis virginiana Kerr Virginia Opossum 20A 13 6 39 Sciurus carolinensis Gmelin Eastern Gray Squirrel 7 7 14 28 Dasypus novemcinctus L. Nine-banded Armadillo 16B 6 0 22 Procyon lotor (L.) Northern Raccoon 7C 1 3 11 Felis catus L. Domestic Cat 4 0 1 5 Sylvilagus floridanus Allen Cottontail Rabbit 2 0 2 4 Canis lupus familiaris L. Domestic Dog 2 1 1 4 Urocyon cinereoargenteus (Schreber) Gray Fox 2 0 1 3 Sciurus niger L. Fox Squirrel 0 2 0 2 Mephitis mephitis (Schreber) Striped Skunk 1 0 1 2 Cheldyra serpentine (L.) Common Snapping Turtle 1 0 0 1 Elaphe obsoleta (Say in James) Rat Snake 1 0 0 1 Crotalus horridus L. Timber Rattlesnake 0 0 1 1 Cathartes aura (L.) Turkey Vulture 1 2 1 4 Cardinalis cardinalis (L.) Northern Cardinal 0 0 2 2 Corvus brachyrhyncos Brehm American Crow 0 1 0 1 Zenaida macroura (L.) Mourning Dove 1 0 0 1 Strix varia Barton Barred Owl 0 1 0 1 Total 83 48 47 178 ASignificant difference (α = 0.05) between US 441 compared to Me-Lo Rd. BSignificant difference (α = 0.05) between US 441 compared to GA 212 and Me-Lo Rd. CSignificant difference (α = 0.05) between US 441 compared to GA 212. Southeastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 182 During each season, an observer drove the survey route each day of one week. During these 28 days of sampling, 27 roadkills were recorded. The length of time roadkills remained on the roadway varied. Most roadkills initially on the asphalt were no longer present within 24 hours (59.3%). Some specimens remained on the roadway for 48 hours (22.2%), and some even ≥72 hours (18.5%). The bony carapace of Armadillos tended to remain long after the flesh was removed. Large roadkills, such as White-tailed Deer, if dead in the roadway and posing a driving hazzard, were likely removed by state workers or civilians. There was no significant difference in the total number of detected roadkills by season (Table 3). The average number of roadkills recorded per month was 14.8, with the highest occurrence in May (n = 21) and the lowest in November (n = 7). Significant seasonal differences (α = 0.05) at the individual species level included White-tailed Deer roadkills more common in winter compared to spring and summer, Opossums found dead more frequently during spring compared to winter and summer, Gray Squirrels found more often during spring compared to winter and fall, and Armadillo roadkills more abundant during summer compared to winter, spring, and fall (Table 3). Roadkills were widely distributed among the various land-cover and obstacle classes (Fig. 1; Tables 4, 5). Overall, the only statistical difference (α = 0.05) was more roadkills in mixed versus forest cover types. Fields accounted for 2.4% of the survey route and were associated with the highest roadkill rate (9.26 RKY). White-tailed Deer roadkills were more commonly associated (α = 0.05) with fields. Mixed land cover, 53% of the survey route, had a slightly lower roadkill rate (8.91 RKY) by comparison. Opossums were detected more frequently (α = 0.05) in mixed versus residential areas. Roadkill rates in residential areas (12.8% of route) were comparable (8.80 RKY) to those in the mixed land cover. Armadillo roadkills were more abundant (α = 0.05) in residential areas compared to forest. Forested areas accounted for the second largest land-cover class (31% of route), but had only 42 observed roadkills and the lowest roadkill rate (6.02 RKY). Areas lacking Table 3. Seasonal records for the five most commonly detected roadkilled species in the Baldwin County, GA, roadkill survey. Each species was observed a minimum of 10 times during the one-year observation period. These five species accounted for 148 of 178 observed roadkills. Winter = December– February; spring = March–May; summer = June–August; fall = September–November. Taxa Winter Spring Summer Fall White-tailed Deer 22A 10 5 11 Virginia Opossum 7 17B 5 10 Eastern Gray Squirrel 4 14C 6 4 Nine-banded Armadillo 1 4 13D 4 Northern Raccoon 4 1 5 1 Total 38 46 34 30 ASignificant difference (α = 0.05) between winter compared to spring and summer. BSignificant difference (α = 0.05) between spring compared to winter and summer. CSignificant difference (α = 0.05) between spring compared to winter and fall. DSignificant difference (α = 0.05) between summer compared to winter, spring, and fall. Southeastern Naturalist 183 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 roadside obstacles accounted for 62.3% of the survey route and the majority (67%) of the roadkills (8.62 RKY). Significantly (α = 0.05) more White-tailed Deer were detected in areas lacking obstacles compared to the mixed class. Segments with a mixed arrangement of obstacles showed the second highest roadkill rate (7.04 RKY). Fenced areas constituted only 1% of the route and, with only one Whitetailed Deer detected, had the lowest frequency of roadkills (4. 55 RKY). Discussion Eighty-seven percent of the roadkilled mammals detected in this study belonged to the five most frequently encountered species: White-tailed Deer, Virginia Table 5. Five most commonly detected roadkill species in each land cover and obstacle class along the roadkill survey route in Baldwin County, GA. See Table 5 for class information. Class Deer Opossum Squirrel Armadillo Raccoon Land cover Field 4A 0 0 0 0 Mixed 28 26B 13 12 8 Residential 5 1 6 6C 1 Forest 9 12 9 4 2 Obstacles Absent 35D 26 20 11 7 Mixed 9 13 8 11 4 Fence 1 0 0 0 0 Total 46 39 28 22 11 ASignificant difference (α = 0.05) between field compared to mixed, residential and forest cover types. BSignificant difference (α = 0.05) between mixed compared to residential cover types. CSignificant difference (α = 0.05) between residential compared to forest cover types. DSignificant difference (α = 0.05) between areas lacking obstacles compared to mixed. Table 4. Observed number of roadkills in each land-cover and obstacle class along the roadkill survey route in Baldwin County, GA. Each class indicates the same spatial pattern present along both sides of the roadway for a minimum of 30 m. Mixed represents conditions where the cover or obstacles along one side of the roadway differs from the other side. Absent indicates no obstacles were present on either side of the roadway. Class Length (km) % total length # roadkills Roadkills/km/yr Land cover Field 0.54 2.4 5 9.26 Mixed 11.79 53.2 105 8.91A Residential 2.84 12.8 25 8.80 Forest 6.98 31.5 42 6.02 Obstacles Absent 13.80 62.2 119 8.62 Mixed 8.10 36.5 57 7.04 Fence 0.22 1.0 1 4.55 ASignificant difference (α = 0.05) between mixed compared to forest cover type. Southeastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 184 Opossum, Eastern Gray Squirrel, Nine-banded Armadillo, and Raccoon. Even though Johnson (1986) questioned the accuracy of the data collected by GA Game and Fish technicians, he found Virginia Opossums, Cottontail Rabbits, Eastern Gray Squirrels, Raccoons, and White-tailed Deer as the most abundant roadkilled mammals in Georgia during the late 1970s and early 1980s. After 30 years, besides the Nine-banded Armadillo, which was not widely established in the state at the time, the same species are generally still the most commonly detected roadkills in the area. The three studies in Florida that recorded all roadkilled species found similar dominant mammalian taxa (Cristoffer 1991, Main and Allen 2002, Smith and Dodd 2003). This high frequency of medium-sized mammals is evident in roadkill species lists from throughout North America (Barthelmess and Brooks 2010, Caro et al. 2000, Conard and Gipson 2006, Glista and DeVault 2008, Seibert and Conover 1991, Smith-Patten and Patten 2008), and is probably due to the greater likelihood of this size carcass remaining on the road after death. Medium-sized mammals are likely to be killed instantly by collisions, are too large to be easily carried from the roadway by scavengers, and remain intact for identification (Main and Allen 2002). In central Georgia, collisions with White-tailed Deer are generally the most dangerous and costly wildlife-vehicle collisions for drivers. White-tailed Deer have variable reproductive seasons in the southern US; however, breeding generally peaks in November (Miller et al. 2003). Nearly half of the recorded roadkilled White-tailed Deer were found in December and January, during the latter half of the breeding season, consistent with observations in other states (Allen and Mc- Cullough 1976, Hubbard et al. 2000, Hussain et al. 2007, McShea et al. 2008). Although it has been suggested that White-tailed Deer may change their behavior in order to avoid habitats near roads because of elevated traffic noise (Forman and Deblinger 2000), it is not evident in Baldwin County. An increase in roadkill frequency during breeding season was evident for Nine-banded Armadillos as well. Nine-banded Armadillos, which breed June through August in Georgia (Layne 2003), were most frequently observed in summer. However, a switch to more nocturnal activity may have resulted in increased roadkill rates in summer months (Inbar and Mayer 1999, Loughry and McDonough 1996) and the relative absence of Nine-banded Armadillo roadkills during the fall and winter was likely associated with their reduced activity during periods of colder weather in central Georgia. For other medium-sized mammals in the US, the correlation of roadkills with seasons appears to vary between regions (Conard and Gipson 2006, Caro et al. 2000, Smith-Patten and Patten 2008). In the Southeast, male Virginia Opossums are more active during the winter, resulting in higher road fatalities during that time of year (Ryser 1995). Patterson and Mead (2008) found a 4:1 male-to-female ratio for roadkilled Virginia Opossums (n = 59) collected in Baldwin County during the winter months of 2002 and 2004. The breeding season for Virginia Opossums in Georgia occurs from late December to mid-January, and may begin again in late summer (Gardner and Sunquist 2003). Virginia Opossums were recorded most frequently in this study in the spring, which does not appear to correlate with the Southeastern Naturalist 185 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 breeding season. However, young Virginia Opossums disperse approximately 120 days following birth (132 days after conception). If adults are breeding in December and early January, then the increase in movement across roadways during April and May could be related to dispersal. The observed increase in Eastern Gray Squirrel roadkills does not appear to correlate with breeding season either. Eastern Gray Squirrels in the Southeast have winter (January–February) and summer (May–July) breeding seasons (Edwards et al. 2003); however, the only increase in Baldwin County Eastern Gray Squirrel roadkills was during spring. This increase could be attributed to the sexual maturation and dispersal of sub-adults prior to the summer breeding season (Edwards et al. 2003). Raccoons have two mating seasons: February–March and May–June (Gehrt 2003). However, the small number of Raccoon roadkills found in this survey did not reveal seasonal correlations. Gehrt (2002) also did not find a correlation between Raccoon roadkills and breeding season, but found that Raccoon road mortality increases with increases in traffic volume to a point above which Raccoons modify their behavior and avoid heavily traveled roads. This behavioral change results in more roadkilled Raccoons found on lesser-traveled roads. However, in our Baldwin County study, significantly more Raccoons were detected on US 441, the busiest section of the survey route, compared to GA 212. The significantly higher overall roadkill rate on US 441 suggests a link between an increased occurrence of roadkills and the numbers of lanes and traffic volume. Baker et al. (2004) found that more medium-sized mammals are killed on major roads like US 441. However, the wider area of asphalt on US 441 and the greater likelihood of noticing a roadkill on the pavement rather than off in the verge may well increase the likelihood of detection there. Jaarsma et al. (2006) concluded that wider roads are associated with higher traffic volume and higher vehicle speed, resulting in increased collisions. Cristoffer (1991) found increased numbers of kills with increased speed, and Alexander et al. (2005) found that road permeability with regards to animal movement across the landscape declines with increased traffic volume. In contrast to the Baldwin County numbers, Clevenger et al. (2003) found lower roadkill rates for mammals on high-volume roads (equivalent to US 441) than low-volume roads (equivalent to GA 212 and Meriwether-Lowe Road). Also, in the southern Great Plains, roadkill rates were higher on 2-lane versus 4-lane roads (Smith-Patten and Patten 2008). Interestingly, on the 2-lane roads in our Baldwin County survey, GA 212 had double the traffic volume of Meriwether/Lowe Road, and a lower roadkill rate. These observations suggest that traffic volume alone may not influence fatal wildlife-vehicle collisions as much as road width combined with traffic volume. Adjacent land cover and roadside obstacles have been shown to influence the frequency of roadkills as well (Main and Allen 2002, Malo et al. 2004). If roadkills are distributed uniformly with respect to land-cover and obstacle classes, we would expect the percentage of roadkills in each class to approximate the class’s proportion of the total route. However, individual species have differing ecological requirements and would not be expected to be evenly distributed among the landSoutheastern Naturalist E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 186 cover types. For all species surveyed, the only significant difference in number of detected roadkill was between mixed and forested areas. The lower roadkill rate in forested areas may be due to lower population densities of common species within the pine monoculture that characterizes most of the forested areas. Virginia Opossums were more often found in mixed compared to residential, and Nine-banded Armadillos were more often observed in residential compared to forest. The low number of roadkilled Virginia Opossums in residential areas was unexpected as they, along with Nine-banded Armadillos, are commonly observed foraging near houses. Kanda et al. (2006) found Virginia Opossum roadkills in central Massachusetts most often associated with human development. As might be expected, the highest roadkill rate (although not significantly different) was found in the areas lacking obstacles. However, the presence of obstacles may not necessarily be reducing the number of roadkills. The obstacles may be funneling animals to wildlife-vehicle collision hotspots. The city of Milledgeville, Baldwin Coounty, is rural with approximately 2990 km of roadways (US Department of Commerce 2005). Considering only mammalian roadkills, 167 were observed on 22.17 km for the year (7.53 RKY). The lowest mammal roadkill rate on any segment of the route was 5.67 RKY on GA 212. Applying this rate to all of the roads in the county, an estimated 17,000 mammals were killed on Baldwin County roads during the one-year study. This estimate is certainly lower than the actual number killed for several reasons. First, we did not detect any mammalian taxa smaller than Eastern Gray Squirrels. Second, considering that Baker et al. (2004) found 24% of roadkilled Vulpes vulpes (L.) (Red Fox) died away from the road and in areas unseen by passing motorists, it is likely that there were many dead animals we did not see from the moving vehicle. Third, Slater (2002), using baits placed along roadways, concluded that the actual number of vertebrate roadkills may be 12–16 times higher than what is observed in a driving survey. Crows were seen foraging along the roads on nearly every survey trip, so perhaps they had already removed smaller roadkill before it was recorded. In addition, Felis catus (Domestic Cat), the sixth most common roadkilled species in the Baldwin County study, has been documented as the dominant nighttime roadway scavenger within 2 km of human residences (Slater 2002). Also, since we surveyed three times a week and the majority of roadkills stayed on the roads for less than 24 hours, and since we recorded 27 roadkills in the 28 days of continuous weekly observations, it is not unreasonable to double our observed number to get a rough estimate of total mammalian roadkills for the county closer to 34,000/year. If this estimate is considered average for the 159 counties in Georgia, then a staggering 5,400,000 mammals are killed on the state’s roadways each year. The use of GIS in this roadkill study allowed for an accurate analysis of spatial variables. However, conducting further research that limits the biases in this study would be beneficial and is needed to understand how and to what magnitude Baldwin County roads are influencing wildlife death rates. Walking a shorter survey route would increase the likelihood of detecting smaller vertebrates and result in a more accurate estimate of yearly roadkills, especially when amphibians are Southeastern Naturalist 187 E.R. Boitet and A.J. Mead 2014 Vol. 13, No. 1 included in sampling. Also, travelling the survey route every day of the week, preferably at sunrise and just prior to sunset, would result in a more accurate estimate. In addition, surveys of residential neighborhoods are needed to assess the difference in roadkill rates compared to low-volume connecting roads like Meriwether/ Lowe Road. The present survey indicates that a large number of roadkills occur on minor roads. Due to their greater abundance on the landscape, minor roads may have a more significant impact on wildlife numbers (Van Langevelde et al. 2009). Roadkills caused by wildlife-vehicle collisions are easily recognized by the general public as an ecologically significant detrimental effect of roads (Forman and Alexander 1998, Smith-Patten and Patten 2008). We currently are witnessing a growing epidemic of vertebrate road mortality in the Southeast, and preventative measures need to be considered to assure the continued survival of our diverse vertebrate fauna. Hopefully, a deeper understanding of what factors are influencing wildlife-vehicle collisions eventually will lead to decreased roadkill numbers across developed areas. Acknowledgments Doug Oetter is graciously thanked for his help with the GIS analysis on this project. The background raster image seen in Figure 1 is from past work by Georgia College GIS classes. We thank Melanie Wooten, Frankie Lee Berry, Matthew Dedecker, and Emily Scarboro for their field assistance. Bob Chandler and Dennis Parmley provided valuable counsel. 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