2011 SOUTHEASTERN NATURALIST 10(1):85–94 Home-Range Size of Evening Bats (Nycticeius humeralis) in Southwestern Georgia Adam D. Morris1,2, Darren A. Miller3,*, and L. Mike Conner1 Abstract - Despite the ecological importance of bats, a lack of basic data, such as spaceuse needs, hinders management efforts. Therefore, we investigated home-range size in Nycticeius humeralis (Evening Bats) by radiotracking 14 individuals (5 females and 9 males) for 7–11 nights each in a pine-dominated landscape in southwestern Georgia during June–August 2008. We generated 95% and 50% adaptive kernel (AK) home ranges and 95% minimum convex polygon (MCP) home ranges and found that mean 95% AK home-range size was 155.7 ± 38.3 ha, with individual values ranging from 36.9 ha to 565.9 ha. Mean 95% MCP home-range size was 118.5 ± 29.5 ha, with individual values ranging from 33.6–456.2 ha. Home-range sizes did not differ between males and females (P = 0.35), but were larger in August (P = 0.004) than in June and July. Evening Bat home-range sizes on our study area were similar to previously documented home ranges in forested and rural landscapes. Although Evening Bats may be habitat generalists relative to foraging activity at the scale of habitat patches, multiple core areas of activity indicate selection within this scale that may be related to prey and roost availability. Introduction Despite the ecological importance of North American bats, habitat and areal requirements of bats within forested systems are not well understood (Miller et al. 2003, Wigley et al. 2007). Estimates of home ranges for bats are seldom reported because of difficulties involved with tracking flying, nocturnal animals (Lacki et al. 2007, Miller et al. 2003) and issues with radiotransmitter weight possibly affecting behavior (Fenton 2003). Furthermore, home ranges of Nycticeius humeralis Rafinesque (Evening Bats), which are important predators of insects within the forests of the southeastern US (Barbour and Davis 1969), have not been well documented (Perry and Thill 2008; but see Carter 1998, Duchamp et al. 2004). Examining home-range dynamics of tree-roosting bats may lead to a better understanding of bat ecology in forested landscapes. Furthermore, homerange information is important for forest and land managers desiring to provide suitable resources for forest bats at the proper scale. While roost location and availability may impact location of home ranges on the landscape (e.g., Menzel et al. 2001a, Miles et al. 2006), home-range size is likely determined by foraging behavior. Evening Bats typically leave the roost for one or more foraging bouts each night (Clem 1993, Duchamp et al. 2004, Wilkinson 1992), and may travel several kilometers during a single foraging bout 1Joseph W. Jones Ecological Research Center, Rt 2 Box 2324, Newton, GA 39870. 2Current address - 1528 Grande Harmony Place, Cary, NC 27513. 3Southern Timberlands Technology, Weyerhaeuser NR Company, PO Box 2288, Columbus, MS 39704. *Corresponding author - darren.miller@weyerhaeuser.com. 86 Southeastern Naturalist Vol. 10, No. 1 (Clem 1993, Wilkinson 1992). Evening Bats demonstrate flexibility in foraging behavior, relative to structural complexity and composition of forest stands, by foraging within pine stands, hardwood forest, and open areas (Carter 1998, Carter et al. 2004, Clem 1993), along forest edges (Carter 1998, Morris et al. 2010), and above forest canopy (Menzel et al. 2000). Evening Bat foraging behavior may also be affected by spatial distribution of food resources (Carter 1998, Wilkinson 1992). Other factors likely to affect the spatial behaviors of Evening Bats include gender (Perry and Thill 2008, Safiet al. 2007), reproductive status (Henry et al. 2002), colony size and density (Meyer et al. 2005), population structure (Safiet al. 2007), and inter-specific competition for roosts (Timpone et al. 2006) or foraging areas (Duchamp et al. 2004). Two previous studies of home ranges of Evening Bats have been conducted in different landscape contexts. The first study, conducted in a diverse forested landscape on the Savannah River Site (SRS) in South Carolina, documented mean (±SE) 95% adaptive kernel (AK) home ranges of 285.3 ± 110.3 ha (Carter 1998). The second study, in a rural landscape undergoing suburban development in Indiana, documented a mean 95% minimum convex polygon (MCP) home range of 303.7 ± 104.9 ha (Duchamp et al. 2004). This landscape was comprised of agricultural areas, woods, and residential areas. Duchamp et al. (2004) noted that in their study Evening Bats roosted exclusively within a small wooded area and consistently foraged in the direction of woodlands and agricultural areas. To better understand areal requirements of Evening Bats, we estimated homerange size for this species on the Joseph W. Jones Ecological Research Center (Ichauway) during the summer of 2008. Because the Ichauway landscape was composed of older-aged Pinus palustris Miller (Longleaf Pine) forest with abundant roost sites that may represent nearly “ideal” evening bat habitat (Miles et al. 2006), we hypothesized that evening bats would be able to secure resources in a smaller area than in other landscapes. We also hypothesized that, because Evening Bats appear to be habitat generalists relative to foraging and due to the relatively ubiquitous habitat structure on Ichauway, Evening Bats would display homogenous space use for foraging and not have areas of high use (i.e., core areas) within home ranges. Field Site Description We conducted our study on Ichauway, located in southwest Georgia (Baker County). The 12,000-ha research site was dominated (68%) by 70–90-year-old second-growth Longleaf Pine stands (Fig. 1), maintained by biennial prescribed burnings. Common midstory species included Quercus falcata Michaux (Southern Red Oak), Liquidambar styraciflua L. (Sweetgum), and other hardwoods. In addition, Pinus spp. (Pine) plantations (11%), hardwood riparian zones (7%), and small agricultural fields/wildlife openings (11%) were scattered throughout the site. The remainder (3%) was buildings, roads, and other infrastructure. We selected this site due to easy access via numerous small dirt roads and because previous research indicated an abundance of Evening Bats on the area (Miles et al. 2005). 2011 A.D. Morris, D.A. Miller, and L.M. Conner 87 Methods We captured bats using mist nets (9 to 18 m long, 2.4 m high) over water at 2 trapping sites for 3–6 consecutive nights each month during June–August 2008. We identified bats to species using standard morphological characteristics, and determined age (adult or juvenile) by shining a light through the wing membrane and examining fusion of the metacarpals. We assessed reproductive condition of female Evening Bats by evidence of lactation. We radiotagged Evening Bats by attaching 0.43-g radiotransmitters (PIP3 radiotags, Biotrack Ltd., UK) to the backs of Evening Bats using surgical adhesive (Perma-Type, Perma-Type Company, Inc., Plainville, CT) after clipping a small area of fur between the scapulae. We only radiotagged bats weighing ≥8.5 g so that radiotransmitters never exceeded 5% of the bat’s body mass (Aldridge and Brigham 1988). We held Evening Bats for 20 minutes to allow adhesive to set and then released them at the site of capture. All animal capture and handling procedures followed guidelines of the American Society of Mammalogists (Gannon et al. 2007). Figure 1. Map of the Joseph W. Jones Ecological Research Center with primary habitat types delineated. 88 Southeastern Naturalist Vol. 10, No. 1 We tracked Evening Bats from emergence until dawn for 7–11 consecutive nights (x̅ = 9.6 nights) until radiotransmitters could no longer be heard. We radiotracked bats using 2 or 3 observers with TRX-2000S receivers (Wildlife Materials, Carbondale, IL) and 3-element yagi antennas. To triangulate bat locations, we communicated via 2-way radios and recorded simultaneous azimuths on bats from numbered, geo-referenced radiotelemetry stations established throughout the study area. As we recorded bearings, we confirmed that the bearings crossed, and that crosses were within the detection range of radiotransmitters (≈0.5 km). We discarded bearings resulting from weak signal strength, and/or because the angle between observer locations was <45 degrees or >135 degrees. To reduce autocorrelation between successive locations, we only analyzed bearings for each bat recorded at least 30 minutes apart (Swihart and Slade 1985). We obtained bat locations based on radiotelemetry data using the program LOCATE II (Nams 2000) and then generated 95% and 50% adaptive kernel (AK) home ranges. We used the adaptive kernel method for home-range estimation because it is less sensitive to fewer locations than other methods and is consistent with the methods of Carter (1998). We also calculated 95% minimum convex polygon home ranges, to make comparisons with the 95% MCP home ranges reported by Duchamp et al. (2004). We calculated 95% MCP home ranges by removing 5% of locations and generating polygons from the remaining locations (Duchamp et al. 2004). For both estimators, we used the Animal Movement Extension (Hooge and Eichenlaub 1997) in Arcview 3.2 (ESRI, Redlands, CA). Although Seaman et al. (1999) suggested that 30 or more locations per animal are necessary for estimation of home range, radiotelemetry studies of bats have often used 20 independent locations as a minimum threshold (e.g., Adam et al. 1994, Carter 1998, Carter et al. 2004, Menzel et al. 2001b). To test whether inclusion of bats with at least 20 telemetry locations was appropriate, we recalculated 95% AK home-range sizes for bats with >30 locations (n = 10) by randomly selecting 20 locations per animal and compared these to full 95% AK home ranges (all points included) using a paired t-test to examine the hypothesis that there was no difference in home-range size estimates from both datasets. We used analysis of variance (ANOVA) to test the hypothesis that 95% AK home-range size did not differ between males and females, and across sampling months (June, July, August) using PROC GLM in SAS (SAS Institute, Inc., Cary, NC). Because we only tracked female bats in June and only male bats in August, we could not test for interaction between sex and sampling month. Therefore, we conducted separate one-way ANOVA tests for simple effects. We used Levene’s test to examine homogeneity of variance, and subsequently applied log-transformations to home-range sizes. We used a t-test to test the hypothesis that 95% AK Evening Bat home ranges on Ichauway did not differ from those reported by Carter (1998) on SRS using log-transformed AK home-range sizes. Similarly, we tested for differences between 95% MCP home ranges in our study and those reported by Duchamp et al. (2004) using square-root-transformed MCP homerange sizes as described in Duchamp et al. (2004). In both analyses, we report back-transformed data in original units. 2011 A.D. Morris, D.A. Miller, and L.M. Conner 89 In addition to home-range size, we examined two measures of home-range configuration: number of centers of activity and number and size of core areas (Elmore et al. 2005). Centers of activity are discrete polygons created by AK that more accurately define an animal’s home range by excluding areas among these centers that contain insufficient locations to warrant inclusion as part of the animal’s home range (see Fig. 2). Core areas are defined as areas of concentrated activity defined by 50% AK contours. Results We captured 81 bats of 5 species (Lasiurus seminolus Rhoads [Seminole Bats; n = 39], Evening Bats [n = 22], Lasiurus borealis Müller [Red Bats; n = 9], Myotis austroriparius Rhoads [Southeastern Bats; n = 7], and Perimyotis subflavus Cuvier [Tricolored Bats; n = 4]) at 2 trapping sites during 15 net nights. We radiotracked 22 Evening Bats during June–August 2008. Home-range sizes generated using 20 randomly selected locations per animal were similar in size to full home ranges (t = 0.75, df = 9, P = 0.47), so we included 4 individuals with 21–27 locations. Therefore, we obtained sufficient radiotelemetry locations from Figure 2. Home-range polygons for 4 Evening Bats (Nycticeius humeralis) radiotracked in southwestern Georgia during June–August 2008. Each discrete polygon is a center of activity as defined by 95% adaptive kernel home ranges, and interior polygons are 50% adaptive kernel core areas. Bat 1 was female; Bats 7, 8, and 13 were males. These four bat home ranges are presented to highlight differences in space-use patterns by individual bats. 90 Southeastern Naturalist Vol. 10, No. 1 14 individuals (x̅ = 30.71 locations; Table 1) including 2 females tracked in June, 3 females and 5 males tracked in July, and 4 males tracked in August (Table 1). Mean (± SE) 95% AK home-range size was 155.7 ± 38.2 ha, with individual values ranging from 36.9–565.9 ha. Mean (± SE) 50% AK core home-range size was 21.4 ± 5.3 ha, with individual values ranging from 4.7–82.8 ha. Core areas comprised 14.4 ± 1.1% of the area of home ranges. Evening Bat AK home-range size did not differ (F1,12 = 0.94, P = 0.35) between males (x̅ = 190.1 ± 60.1, n = 9) and females (x̅ = 93.8 ± 19.5, n = 5), but varied with sampling month (F2,11 = 9.39, P = 0.004), with largest home ranges in August (Table 1). Evening Bat AK home ranges contained 1–7 centers of activity (x̅ = 3.4 ± 0.4) and 1–3 core areas (x̅ = 1.5 ± 0.2; Table 1; Fig. 2). Evening bat home ranges were composed of mature pine stands (51.7 ± 2.7%), hardwood riparian zones (32.1 ± 3.5%), open fields (15.5 ± 1.8%), and pine plantations (3.2 ± 1.0%). In addition, home ranges contained 1–4 sources of water (x̅ = 2.2 ± 0.3). Evening Bat 95% AK home-range sizes on Ichauway (n = 14) were not different (t = 1.05, df = 18, P = 0.31) from 95% AK home-range sizes (n = 6) on the Savannah River Site (x̅ = 285.3 ha; range = 38.7–761.0 ha; Carter 1998). Mean (± SE) 95% MCP home-range size was 118.5 ± 29.5 ha, with values ranging from 33.61– 456.2 ha. Evening Bat 95% MCP home ranges on Ichauway (n = 14) were not different (t = 1.7, df = 13; P = 0.11) from 95% MCP home ranges on a rural landscape (x̅ = 303.7 ha, n = 11) reported by Duchamp et al. (2004). Discussion Consistent with studies of other bat species (Adam et al. 1994, Elmore et al. 2005, Menzel et al. 2005), we did not detect differences in home-range sizes Table 1. Ninety-five percent and 50% adaptive kernel home ranges (AK; hectares), and 95% minimum convex polygon home ranges (MCP; hectares) from bat radiotelemetry locations obtained during June–August 2008 for Evening Bats, Nycticeius humeralis (n = 14), on Ichauway, southwestern Georgia. Bat data include sex (F = female; M = male), age (J = juvenile; A = adult); reproductive status (Status: L = evidence of current or past lactation, S = evidence of scrotal development, N = non-reproductive), tracking period (Month), number of nights tracked (Nights), number of radiotelemetry locations (Locations), and number of core areas (Cores). Bat Sex Age Status Month Nights Locations Cores 95% AK 50% AK 95% MCP 1 F A L June 7 24 2 137 21 73 2 F A L June 8 21 1 75 19 46 3 F J N July 11 32 1 135 18 110 4 F A L July 11 30 2 64 17 75 5 F A L July 11 24 1 58 7 36 6 M A S July 11 33 1 161 12 139 7 M A S July 11 31 1 115 26 90 8 M A S July 7 31 1 37 13 52 9 M A S July 11 30 3 55 5 34 10 M A N July 11 27 1 50 9 42 11 M A S August 9 42 1 200 6 158 12 M A S August 9 36 1 189 23 141 13 M A S August 8 35 3 338 38 208 14 M A S August 9 34 2 566 83 456 2011 A.D. Morris, D.A. Miller, and L.M. Conner 91 among male and female Evening Bats, although differences between males and females may not have been detected if they were dependent on sampling month. We did find that home-range sizes of male Evening Bats increased as summer progressed, but, as we did not track any female bats in August, we do not know if females exhibit the same pattern. Regardless, Carter (1998) also found that Evening Bat home-range size increased in August, which may be related to breeding activity (Baker and Ward 1967, Whitaker and Hamilton 1998). Likewise, in our study, all males were reproductive (i.e., scrotal) in July and August (Table 1), indicating the onset of breeding activity. Evening Bat home ranges on Ichauway contained pine and hardwood forest stands, open areas, and one or more sources of water. Mature pine and hardwood stands contained suitable roosting sites for Evening Bats (Miles et al. 2006), while pine stands, open areas, and forest edges are suitable foraging sites (Carter 1998, Morris et al. 2010). Accessible sources of water are important for forest bats, which drink and forage over open water (Vindigni et al. 2009). Counter to our expectations, home-range sizes of Evening Bats in this study were similar to those recorded on the SRS, a forested landscape in South Carolina (Carter 1998), and to those on a fragmented landscape in Indiana (Duchamp et al. 2004). Similar to our study area, SRS was a mostly forested landscape in the coastal plain containing pine and hardwood forest types (Carter 1998). However, the Indiana landscape was composed of agricultural fields and woodlands (Duchamp et al. 2004). It is unclear why home-range sizes were so similar among all three of these areas, although it may be related to the ability of Evening Bats to forage across a wide range of habitat conditions (e.g., Carter 1998, Carter et al. 2004, Clem 1993, Morris et al. 2010). However, as sample sizes in all these studies are small, it is also possible that these results are spurious. More research is needed relative to space use needs of Evening Bats. Also counter to our expectations, even though overall home-range sizes of Evening Bats were similar among landscapes, Evening Bat home ranges in our study often contained multiple core areas (Fig. 2), reflective of areas of intense use. Evening Bats on our study area preferred mature pine and open areas at the home-range scale (Morris et al. 2009). However, Evening Bats may have selected these areas of intense use due to unmeasured factors such as availability of multiple roost sites in a small area (e.g., Bowles et al. 1996, Duchamp et al. 2004, Menzel et al. 2001b, Miles et al. 2006) or patchy distribution of food resources (Carter 1998, Wilkinson 1992). Additionally, the widespread centers of activity may reflect alternate foraging routes in response to fluctuating prey densities (Wilkinson 1992). In both cases, it appears that Evening Bats, although considered to be habitat generalists during foraging, may be selective of foraging areas within home ranges based on factors such as roost and prey availability. However, as it is unclear which characteristics make these core areas attractive to Evening Bats, more research is needed to understand factors contributing to use of core areas to allow improvement of management recommendations for this species and increase understanding of the basic ecology of Evening Bats relative to space-use patterns. Regardless, it appears that management for this species 92 Southeastern Naturalist Vol. 10, No. 1 should be considered at the landscape scale given differences in habitat selection at different scales (Morris et al. 2009) and the general need to manage for bats across a landscape (Duchamp et al. 2007). Acknowledgments Funding for this study was provided by the National Council for Air and Stream Improvement (NCASI), Weyerhaeuser NR Company, and the Joseph W. Jones Ecological Research Center. We thank T.B. Wigley, B. Howze, J. Rutledge, J. Brock, M. Munroe, J. Swart, and J. Miller for their assistance. We also thank M. 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