Northeastern Naturalist 168 J.J. Huebschman 22001199 NORTHEASTERN NATURALIST 2V6(o1l). :2166,8 N–1o8. 21 Bats in Southwest Wisconsin During the Era of White-nose Syndrome Jeffrey J. Huebschman* Abstract - Since 2004, my students and I have caught and examined 1441 individual bats representing 7 species from mist-net surveys in Grant County, WI. Across all years and sites, Myotis lucifugus (Little Brown Bat) was the most frequently captured bat (59.6% of all captures). We captured over 78% (n = 1106) of bats within the first 120 min after sunset. Based on the capture of lactating females, the following species raise young in southwest Wisconsin: Eptesicus fuscus (Big Brown Bat), Perimyotis subflavus (Tri-colored Bat), Little Brown Bat, M. septentrionalis (Northern Long-eared Bat), Lasiurus borealis (Eastern Red Bat), and L. cinereus (Hoary Bat). Secondary sexual dimorphism was most evident in Big Brown Bats and Eastern Red Bats. Trends at 1 primary research site for the 3 most commonly captured species showed that, from 2007 to 2017, there was no significant change in number of bats captured per mist-net-meter-hour for Big Brown Bats and Eastern Red Bats. In contrast, and coincident with the occurrence of white-nose syndrome in Wisconsin, there was a signicant decline in the number of Little Brown Bats captured per mist-net-meterhour over that same time period. Monitoring of bat populations in southwest Wisconsin should continue. Introduction The published literature on Wisconsin’s bats was originally summarized by Cory (1912). Later, in his definitive statewide treatise on Wisconsin’s mammals, Jackson (1961) again summarized the literature on Wisconsin’s bats and supplemented the accounts of others with his own detailed notes. Subsequently, Long (1976) provided an update on the status of Wisconsin’s bats and, in his own comprehensive account of Wisconsin’s mammals, provided a further summary (Long 2008). These reviews summarized information on Wisconsin’s bat species, such as their distribution, relative abundance, sex ratios, habitat use, hibernation activities, and reproduction. However, these accounts were necessarily broad in scope, given their statewide coverage, and also predated the regional occurrence of white-nose syndrome (WNS), which was first detected in Wisconsin bats in 2014 (whitenosesyndrome.org). Bat mortality at WNS-affected sites is in excess of 75% (Blehert et al. 2009), and summer populations of species vulnerable to WNS are declining (Dzal 2010, Francl et al. 2012, Powers et al. 2015). In Wisconsin, bats infected with WNS were first detected in spring 2014 in Grant County, located in the southwest corner of the state. Since that time, WNS-affected sites have been documented throughout the state and in adjacent counties in Illinois and Iowa (whitenosesyndrome.org). *Department of Biology, University of Wisconsin-Platteville, 1 University Plaza, Platteville, WI 53818; huebschj@uwplatt.edu. Manuscript Editor: Joseph Johnson Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 169 Scientists at the National Wildlife Health Center, a science center of the US Geological Survey, located in Madison, WI, have utilized Wisconsin bats in studies on WNS and its impacts on bats (Cryan et al. 2013, Lindner et al. 2011, Verant et al. 2014), but the specific impacts of WNS on summer bat communities in southwest Wisconsin have not yet been reported. Since 2004, I have conducted bat mist-netting surveys in Grant County, WI (Fig. 1). In that period, my students and I have caught and examined 1441 individual bats, representing 7 species. Bats in southwest Wisconsin have been specifically investigated once prior to my study (Ainslie 1983). Ainslie (1983) conducted mistnet surveys from 28 May to 18 August 1981 in Grant, Crawford, Vernon, Richland, Sauk, Iowa, and Lafayette counties—all located in southwest Wisconsin—and he also conducted harp-trap surveys from 7 April to 7 May and from 13 August to 18 September at the entrances of 3 hibernation sites from Grant, Sauk, and Iowa counties. Ainslie (1983) reported relative abundance of bats from the region, but only limited natural-history information. The purpose of my study was to provide an account of the natural history of bats from southwest Wisconsin derived from my long-term survey efforts and to report changes in capture rates of summer bats within the region during the era of WNS. Figure 1. Locations of bat mist-netting sites within Grant County, WI, with relative size of icon based on overall percent of captures of bats at each site during the 2004–2017 study duration. Sites are numbered in order of percent of bat captures, which was reflective of variation in survey nights among sites (Table 1): (1) UW-Platteville Campus, (2) Stanton Road, (3) Condry Road, (4) Rock Road, (5) Eagle Valley, (6) Sand Hill Road, (7) Atkinson Road, (8) Fenley Wildlife Management Area, (9) Rountree Trail, and (10) Baker Ford Road. Northeastern Naturalist 170 J.J. Huebschman 2019 Vol. 26, No. 1 Study Area Grant County, WI, is located within the Driftless Area, a region of ~39,000 km2 covering southwestern Wisconsin and adjacent areas in Illinois, Iowa, and Minnesota that were never covered by continental glaciers during the Pleistocene (Hartley 1966). Grant County is bordered on the west by the Mississippi River and to the north by the Wisconsin River. Within southwest Wisconsin, the Driftless Area is characterized by topography that varies from gently rolling to rugged and deeply dissected, with small streams throughout the region. Upland areas were historically prairie or savanna habitat (Curtis 1959, Hartley 1966), most of which has been converted to agricultural land, including both row crops and pasture. Upland woodlands include Acer spp. (maple), Tilia americana L. (American Basswood), Quercus spp. (oak), Celtis occidentalis L. (Hackberry), Ostrya virginiana Mill. (Eastern Hophornbeam), and Juglans nigra L. (Black Walnut) (Curtis 1959). Floodplain forests occur along the Mississippi and Wisconsin Rivers and are dominated by A. saccharinum L. (Silver Maple), Populus deltoides W. Bartram ex Marshall (Eastern Cottonwood), Ulmus spp. (elm), Salix nigra Marshall (Black Willow), and Fraxinus spp. (ash) (Curtis 1959). Particularly in deep ravines, slope aspect can have a large impact on microclimate, which also impacts vegetation (Curtis 1959). Outcrops of Paleozoic bedrock occur throughout the area, in addition to many active and abandoned rock quarries (Dott and Attig 2004). The greenspace adjacent to the Rountree Branch stream on the University of Wisconsin-Platteville campus was the primary survey area throughout the study period (Fig. 1). Throughout most of the greenspace, the stream is bordered by deciduous trees, including A. negundo L. (Boxelder), Morus sp. (mulberry), American Basswood, and oaks in adjacent uplands. Close to the stream corridor there were areas of mown lawn, a reestablished prairie, rock outcrops, and an old quary site. Netting sites on the UW-Platteville campus thus were characteristic of many features found at other survey sites used during this study. Unfortunately, a tornado hit the campus greenspace on 16 June 2014, destroying 1 primary mist-netting location and dramatically impacting a second. In addition to survey sites on the UW-Platteville campus, my students and I surveyed 9 other sites within the Driftleass Area during the course of this study (Fig. 1). Methods To survey bats, we employed mist-nets strung in flight corridors over streams from May through September. We set nets up before sunset and attended them continuously until closure (frequently 3–3.5 h after sunset). Typically, we used 2–3 nets at each location. Mist-nets varied in length from 6 m to 12 m, depending on the width of the flight corridor; all nets were 2.6 m high. We removed captured bats from nets and placed them in paper drinking cups with plastic lids as soon as they were detected. For all captured bats, we recorded species, sex, reproductive condition, age (adult or young-of-the-year [YOY]), forearm length, and mass. We assessed reproductive condition according to Racey (1988) and age-class by Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 171 examining the degree of closure of the phalangeal epiphyses (Anthony 1988). We weighed bats on an electronic balance (OHAUS model CS200; OHAUS, Parsippany, NJ). Results reported here are a compilation of several short-term projects. Naturalhistory information—such as sex ratios, reproductive patterns, and morphological data—is based on results from all sites across all years, unless otherwise stated. For each species, we calculated relative frequency of bats captured after sunset for each 30-min increment up to 3.5 h after sunset. I report trends in capture rates from the Stanton Road site, which has been the least modified (by natural or artificial perturbations) and continuously surveyed the longest (i.e., since 2007). To accommodate variation in annual sampling effort, I calculated bats per mist-net-meter-hour for that site and regressed that value against sampling year. I calculated mist-net-meterhour as the total linear meters of mist-net deployed on a given night multiplied by the number of hours nets were open. For each year, I divided the sum of all bats captured by the total mist-net-meter-hours for each species. I conducted linear regression to investigate the relationship between bats per mist-net-meter-hour and survey year to determine if capture frequency for species varied over time, and employed a chi-square test to determine if bat sex was independent of age-class. I tested secondary sexual dimorphism in average forearm length of adult bats with a two-sample t-test, assuming unequal variances. I also tested differences in average mass between adult males and adult females and between YOY males and YOY females with a 2-sample t-test, assuming unequal variances; only bats captured after 9 July, which was after the pregnancy period in females, and also around the time when flying YOY bats had been detected for most species, were included in these tests. If a significant (P < 0.05) difference was detected, I calculated Cohen’s d (Cohen 1988), which standardizes effect size, by following Vu et al. (2018), who determined Cohen’s d using the pooled-sample standard deviation. Using this approach, values ≥0.8 are considered large effects and values of ~0.5 are considered moderate effects (Cohen 1988). I also determined 95% confidence intervals for Cohen’s d, using the approach detailed by Hedges and Olkin (1985), which is: 95% CI: d – 1.96 * σ[d] to d + 1.96 * σ[d] We followed protocols designed to reduce the unintentional spread of WNS (whitenosesyndrome.org) when handling bats and cleaning equipment. Methods for capturing and handling bats followed the guidelines of the American Society for Mammalogists (Sikes et al. 2016) and were approved by the UW-Platteville Animal Care and Use Committee. Results We captured a total of 1441 bats, representing 7 species, during 126 survey nights from 2004 to 2017 (Table 1). Across all years, the earliest survey date was 12 May and the latest survey date was 22 September. Survey nights were distributed relatively evenly between June (27.2% of survey nights), July (30.4%), and August (25.6%), with fewer survey nights in September (11.2%) and May (5.6%). Across Northeastern Naturalist 172 J.J. Huebschman 2019 Vol. 26, No. 1 all years and sites, Myotis lucifugus Le Conte (Little Brown Bat), was the most frequently captured bat (59.6% of all captures), followed by Eptesicus fuscus Palisot de Beauvois (Big Brown Bat) (19.3%), Lasiurus borealis Müller (Eastern Red Bat) (11.4%), Perimyotis subflavus F. Cuvier (Tri-colored Bat) (5.1%), M. septentrionalis Trouessart (Northern Long-eared Bat) (3.5%), L. cinereus Palisot de Beauvois (Hoary Bat) (0.7%), and Lasionycteris noctivagans Le Conte (Silver-haired Bat) (0.3%) (Table 1). Most survey nights occurred at UW-Platteville campus sites (50%), followed by Stanton Road (21.4%); the remaining survey nights were split among the 8 remaining survey sites (Table 1). We captured >78% (n = 1106) of bats within the first 120 min after sunset, with >54% (n = 772) of all captures occurring 31–90 min after sunset (Fig. 2). The peak period of capture for the Little Brown Bat, Eastern Red Bat, Tri-colored Bat, and Northern Long-eared Bat occurred 31–60 min after sunset, whereas the peak period of capture for the Big Brown Bat was 61–90 min after sunset (Fig. 2). Bat captures declined steadily over the course of the evening after the peak period of captures (Fig. 2). Most of the few Hoary Bat captures (78%; n = 7) occurred later in the evening, 121–210 min after sunset. Adult sex ratios were skewed toward males for Tri-colored Bats (1.27 M:F) and Little Brown Bats (2.68 M:F), and toward females for Northern Long-eared Bats (0.52 M:F) and Eastern Red Bats (0.58 M:F) (Table 2). Adult sex ratios were nearly even for Big Brown Bats (0.98 M:F) (Table 2). For all species, sex ratios in YOY bats skewed towards males (Table 2). Bat sex was not independent of age-class for Little Brown Bats (χ2 = 8.93, df = 1, P = 0.003 ) and Eastern Red Bats (χ2 = 4.00, df = 1, P = 0.045), indicating that sex ratios differed between age-classes for these species. Over the course of the full study period, we captured lactating bats from 6 of 7 species (Fig. 3), as evidenced by expressed milk. We captured no lactating Table 1. Bats captured at survey sites in Grant County, WI, from 2004 to 2017. The number of survey nights and the total number of captures by species are indicated for each site. Bat species: BB = Big Brown, T-c = Tri-colored, LB = Little Brown, NL = Northern Long-eared, ER = Eastern Red, H = Hoary, and S-h = Silver-haired. Number of bats captured by species Years Survey Site surveyed nights BB T-c LB NL ER H S-h 1. UW-P Campus 2004–17 63 103 22 539 26 40 3 1 2. Stanton Road 2007–17 27 95 17 82 9 41 6 0 3. Condry Road 2007–2010 10 34 24 27 1 32 0 3 4. Rock Road 2007–2010 10 29 3 70 4 26 1 0 5. Eagle Valley 2011 5 1 3 52 3 4 0 0 6. Sand Hill Road 2016–17 4 11 0 0 4 20 0 0 7. Atkinson Road 2011–12 3 2 4 28 0 0 0 1 8. Fenley WMA 2007 2 0 1 47 3 0 0 0 9. Rountree Trail 2008 1 3 0 6 1 1 0 0 10. Baker Ford Road 2007 1 0 0 8 0 0 0 0 Totals 126 278 74 859 51 164 10 5 Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 173 Silver-haired Bats during this study. We captured most (69%, n = 68) lactating bats between 21 June and 10 July (Fig. 3). The earliest documented lactating bats in this study were 2 Eastern Red Bats captured on 6 June 2012. The latest record of a lactating bat in this study was a Big Brown Bat captured on 11 August 2009. Capture of a lactating Hoary Bat on 3 July 2012 is evidence that this species raises young in southwest Wisconsin. Figure 2. Time of capture in 30-min increments after sunset for all bat species, shown as a percent of all captures (n = 1440) for bats caught in Grant County, WI, between 2004 and 2017. Table 2. Number of males and females of known-age adults and flying young-of-the-year (YOY) based on mist-net captures from all sites and survey years. Male to female (M:F) sex-ratios for both age-classes for each species are shown. P-value from a chi-square test to determine if bat sex was independent of age-class; P ≤ 0.05 indicates sex was statistically not independent of age class. We captured 4 additional Silver-haired Bats (2 males and 2 females) in September and their age-class could not be unequivocally assigned; thus, they are not included here. Adults YOY Bat species Males Females M:F Males Females M:F P-value Big Brown 97 99 0.98 35 28 1.25 0.40 Tri-colored 28 22 1.27 9 5 1.80 0.58 Little Brown 498 186 2.68 81 54 1.50 less than 0.01 Northern Long-eared 13 25 0.52 4 4 1.00 0.40 Eastern Red 32 55 0.58 34 30 1.13 0.05 Hoary 0 1 NA 4 2 2.00 0.21 Silver-haired 0 0 - 1 0 NA - Northeastern Naturalist 174 J.J. Huebschman 2019 Vol. 26, No. 1 We documented flying YOY for all species captured in this study (Table 3). The earliest detected flying YOY was a male Big Brown Bat captured on 28 June 2012. For most species, the earliest dates of flying YOY occurred in mid- to late July (Table 3). First occurrences of flying YOY for both the Tri-colored Bat and the Silver-haired Bat were later in this study; the earliest flying YOY Tri-colored Bat was documented on 31 July 2007, and the only definitively aged flying YOY Silverhaired Bat was captured on 22 August 2012 (Table 3). We captured Silver-haired Bats only during late summer and early fall, when age determination by epiphyseal closure is often inconclusive. In addition to the Silver-haired Bat captured on 22 August, we captured 1 individual on 2 September 2009, and 3 individuals on 13 September 2007. Figure 3. Percent of lactating bats during a given date interval, shown as a percent of all lactating bats (n = 99) caught in Grant County, WI, between 2004 and 2017. Table 3. Earliest dates of capture for flying young-of-the-year (YOY) bats at survey sites in Grant County, WI, from 2004–2017. Bat species Male Female Big Brown 28 June 2012 21 July 2015 Tri-colored 2 August 2012 31 July 2007 Little Brown 10 July 2012 10 July 2012 Northern Long-eared 12 July 2016 17 July 2012 Eastern Red 11 July 2012 17 July 2012 Hoary 22 July 2014 24 July 2013 Silver-haired 22 August 2012 - Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 175 Secondary sexual dimorphism was evident in adult Big Brown Bats and Eastern Red Bats via differences in FA length; in each of these species female FA length was significantly (P < 0.05) larger than male FA length (Table 4) and Cohen’s d was near, or greater than 0.8, for both species (Table 5), indicating a large size effect. Although average FA length differed significantly (P = 0.01) between sexes in Little Brown Bats, the small Cohen’s d and an upper limit of the 95% confidence interval of d below 0.5 (Table 5), indicated no biologically significant difference in FA size. Adult female mass (after 9 July) was significantly greater than males for most species (P < 0.05; Table 6), and for the species that differed significantly, Cohen’s d was greater than 0.8. Only in Eastern Red Bats did average mass of YOY differ significantly between sexes (Table 6) and show a large effects difference (Table 5). In YOY Little Brown Bats, average mass differed significantly (Table 6), and there was a moderate size effect (Table 5). Trends in capture rate at Stanton Road showed that from 2007 to 2017 there was no significant change in number of bats captured per mist-net-meter-hour for Big Brown Bats (n = 11, r² = 0.01, P = 0.812) and Eastern Red Bats (n = 11, r² = 0.01, P = 0.760). In contrast, there was a signicant decline in the number of Little Brown Bats captured per mist-net-meter-hour over the same time period (n = 11, r² = 0.59, P = 0.006; Fig. 4). Capture-rate trends for both the Tri-colored Bat and the Northern Long-eared Bat were negative, but these trends were not significant for Table 5. Cohen’s d, which is the standardized effect size (indicated by an asterisk [*]), with associated lower and upper limits of the 95% confidencd intervals of d. Values are reported for all tests of secondary sexual dimorphism where significant P-values (P ≤ 0.05) from 2-sample t-tests were reported (Tables 4, 6). Values of Cohen’s d ≥ 0.8 are considered large effects and values of ~0.5 are considered moderate effects (Cohen 1988). Bat species FA Adult Mass YOY mass Big Brown 0.44 – 0.73* – 1.02 0.69 – 1.11* – 1.53 Tri-colored 0.06 – 0.76* – 1.45 Little Brown 0.06 – 0.23* – 0.40 0.14 – 0.37* – 0.61 0.24 – 0.60* – 0.96 Northern Long-eared 0.22 – 1.27* – 2.32 Eastern Red 0.87 – 1.35* – 1.83 1.06 – 1.76* – 2.46 1.18 – 1.76* – 2.34 Table 4. Mean forearm (FA) length (in mm), standard deviation (SD), and sample size (n) of adult male and female bats captured in Grant County, WI, from 2004 to 2017. P-values provided were derived from a 2-sample t-test to examine secondary sexual dimorphism in mean forearm length; significant differences indicated by asterisk (*). Male FA Female FA Bat species Mean SD n Mean SD n P-value Big Brown 45.15 2.07 97 46.52 1.66 97 less than 0.01* Tri-colored 34.08 1.23 28 34.37 1.06 22 0.37 Little Brown 37.39 1.07 497 37.63 1.16 185 0.01* Northern Long-eared 35.55 1.51 13 36.10 0.69 25 0.23 Eastern Red 38.73 1.06 32 40.74 1.70 54 less than 0.01* Hoary - - - 56.50 - 1 - Silver-haired - - - - - - - Northeastern Naturalist 176 J.J. Huebschman 2019 Vol. 26, No. 1 Table 6. Mean mass (g), standard deviation (SD), and sample size (n) of adult and flying young-ofthe- year (YOY) male and female bats captured in Grant County, WI, from 2004 to 2017. YOY values given in parentheses. P-values are from a 2-sample t-test to examine secondary sexual dimorphism in mean mass; significant differences indicated by asterisk (*). Male mass, adult (YOY) Female mass, adult (YOY) Bat species Mean SD n Mean SD n P-value Big Brown 18.14 2.49 57 20.85 2.37 46 less than 0.001* (15.08) (1.81) (34) (16.27) (2.77) (27) (0.061) Tri-colored 6.53 1.02 18 7.24 0.85 16 0.033* (6.29) (0.49) (9) (5.92) (0.61) (5) (0.282) Little Brown 8.15 1.31 278 8.63 1.24 96 0.001* (7.04) (0.70) (79) (7.47) (0.75) (51) (0.001)* Northern Long-eared 6.25 0.49 6 6.88 0.50 13 0.028* (5.95) (0.45) (4) (6.15) (0.17) (4) (0.454) Eastern Red 11.31 0.89 18 13.73 1.62 27 less than 0.001* (9.42) (1.03) (34) (11.63) (1.46) (30) (less than 0.001)* Hoary (21.20) (2.38) (4) (23.3, 26.9) - (2)A (0.212) Silver-haired (10.4) - (1) - - - - AAdult female prior to 10 July. Figure 4. Capture-rate trends from 2007 to 2017 at Stanton Road for the 3 most commonly captured species, reported as bats per mist-net-meter-hour. The relationship between bats per mist-net-meter-hour and survey year was not significant for Big Brown Bats (n = 11, r² = 0.01, P = 0.812) or Eastern Red Bats (n = 11, r ² = 0.01, P = 0.760). The number of Little Brown Bats captured per mist-net-meter-hour over that same time period declined significantly (n = 11, r ² = 0.59, P = 0.006). Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 177 either species (Tri-colored Bat: n = 11, r² = 0.23, P = 0.132; Northern Long-eared Bat: n = 11, r² = 0.30, P = 0.079). Discussion In my study, the Little Brown Bat, Big Brown Bat, and Eastern Red Bat were the 3 most commonly captured species, collectively accounting for over 90% of bat captures across all years and sites. These 3 species comprised nearly 94% of bats captured in mist-nets in Ainslie’s (1983) study, and others have variously noted the abundance of these species in Wisconsin (Jackson 1961; Long 1976, 2008). Specifically, Jackson (1961) noted that the Little Brown Bat was possibly the most abundant bat in Wisconsin, particularly in proximity to buildings. Long (1976, 2008) likewise noted that the Little Brown Bat may be the most common bat in the state, and Ainslie (1983) found it to be the most common bat in southwest Wisconsin. In this study, the Little Brown Bat was also the species most frequently captured, and it was found at the most locations (Table 1). Although Jackson (1961) indicated that the Big Brown Bat was not abundant in Wisconsin, Long (1976) considered it abundant and recently reiterated that point (Long 2008). In southwest Wisconsin, the Big Brown Bat was the fourth most abundant species Ainslie (1983) captured in summer; in my study it was the second most common species caught, found at 8 of 10 survey sites and accounting for over 19% of all captures (across all sites and years). In Wisconsin, both the Little Brown Bat and Big Brown Bat benefit from the use of natural and artificial roosts, such as buildings (Jackson 1961, Long 2008). Highlighting their use of artificial roosts, over 98% of bats captured from barns and rural buildings in south-central Iowa were Little Brown Bats and Big Brown Bats (Benedit et al. 2017). In Ainslie’s (1983) study, the Eastern Red Bat was the second most commonly captured bat during summer mist-net surveys in southwest Wisconsin, but only comprised ~6% of all mist-net captures, in contrast to over 11% of mist-net captures in my study. I acknowledge that differences in mist-netting protocols impact the ability to directly compare my results with those from prior studies because mist-netting protocols can have statistically significant effects on the capture rates of species (Winhold and Kurta 2008). In spite of this caveat, the overall numeric dominance of the Little Brown Bat, Big Brown Bat, and Eastern Red Bat in this study is consistent with prior studies for this region. The species less commonly captured in my study included the Tri-colored, Northern Long-eared, Hoary, and Silver-haired bats (Table 1). Of note, Nycticeius humeralis Rafinesque (Evening Bat), which was recently documented in Wisconsin for the first time (Kaarakka et al. 2018) along the Illinois border in the central part of the state, was not detected in this long-term study, but it may be in the future with continued range expansion. Tri-colored Bats have not been captured since 2015 (when we captured only 1 in 9 survey nights), and no Northern Long-eared Bats were captured in 2017. Both of these species, in addition to the Little Brown Bat, have experienced population declines due to WNS in other regions (Moosman et al. 2013, Reynolds et al. 2016, Silvis et al. 2016), with the Northern Long-eared Bat potentially at greatest risk of local extinction (Frick et al. 2015). Along with the Northeastern Naturalist 178 J.J. Huebschman 2019 Vol. 26, No. 1 Eastern Red Bat, both Hoary Bats and Silver-haired Bats generally migrate out of Wisconsin during winter months (Cryan 2003, Long 2008). In contrast to Eastern Red Bats, Hoary Bats and Silver-haired Bats are generally rare in Wisconsin (Long 2008). In my study, Hoary Bat capture rate may have been influenced by their later activity period, which peaks up to 5 h after sunset (Kurta 1995). Consistent with that result, we captured Hoary Bats later in the evening than most other bats in this study. Regarding the Silver-haired Bat, Long (2008) indicated that they are seldom taken in Wisconsin anywhere other than along the western shore of Lake Michigan and that their habits are poorly known. Incremental additions to the natural history of these species in Wisconsin remain valuable. The capture of most bats within the first 2 h after sunset in th is study (Fig. 2) is consistent with that reported by Miller (2003) in Mississippi. Although the suite of species differed, Miller (2003) reported that 78% of all bats were captured within the first 120 min after sunset, as was the case in this study. Winhold and Kurta (2008) examined captures from the fifth hour of netting (after sunset) compared to the prior 4 h collectively, and showed that differences of as little as 1 h in netting duration can impact the comparability of results from mist-netting studies. Although there was some variation in the duration of netting time over the years of this study, all netting nights included the period of greatest bat activity. Adult sex ratios were skewed for 4 of 5 species in this study, and YOY sex ratios differed significantly from adult sex ratios for 2 species (Table 2). In his study from southwest Wisconsin, Ainslie (1983) reported a sex ratio only for Little Brown Bats and it was skewed towards males (1.21M:F), but he did not indicate whether this metric was based only on adults, or on bats of both age-classes. Sex ratios of adult bats are frequently skewed (Kurta 2010), and others have reported differing sex ratios between adult and YOY bats from within a region (Miller 2003). Many factors influence sex ratios of bats within a region, including temperature (Ford et al. 2002), mating opportunities (Burns and Broder 2015), proximity to roost sites (Broders and Forbes 2004), and differential, sex-based surival (Frick et al. 2010b). As such, explanations of sex ratios found in this study are likely not reduceable to a single factor. Based on the capture of lactating females, I conclude that Big Brown, Tricolored, Little Brown, Northern Long-eared, Eastern Red, and Hoary bats all raise young in southwest Wisconsin. All of these species, plus the Silver-haired Bat, were also captured as flying YOY in this study. In southwest Wisconsin, the highest percentage of lactating bats occurred primarily from late June to mid-July, with some individuals starting earlier or continuing later than this period. These findings were not previously reported for this region in accounts of Wisconsin bats (Ainslie 1983; Jackson 1961; Long 1976, 2008). In southwest Wisconsin, secondary sexual dimorphism was most evident among Big Brown and Eastern Red Bats, where adults differred in both FA size and mass. Adult female mass was nearly 18% greater than male mass in Eastern Red Bats and 13% greater in Big Brown Bats. To put this size difference in context, current guidelines recommended that radio-transmittors on bats should Northeastern Naturalist Vol. 26, No. 1 J.J. Huebschman 2019 179 ideally be less than 5–10% of the animal’s mass (Sikes et al. 2011). So to equal the mass of females (on average), males would need a mass addition greater than the maximum recommended for radio-transmitters. Larger size in female vespertilionid bats is hypothesized to be driven by the female demands of caring for and transporting young bats, both in utero and after parturition (Myers 1978), as well as energetic demands of rapid embryonic development of young; and increased capacity for storing energy reserves (Williams and Findley 1979). Although the Little Brown Bat was the most frequently captured species during this study period, in recent years, the effects of WNS on this species have become apparent. At the Stanton Road site, Little Brown Bat capture rates have declined significantly, in contrast to the capture rates for Big Brown Bats and Eastern Red Bats (Fig. 4). These findings are generally consistent with the pre- and post-WNS metrics for these species in West Virginia (Francl et al. 2012), New Hampshire (Moosman et al. 2013), and Indiana (Pettit and O’Keefe 2017). The impacts of WNS on Big Brown Bats are not as deliterious as they are on Little Brown Bats (Frank et al. 2014, Moore et al. 2017), and Eastern Red Bats have shown no diagnostic signs of infection with WNS (whitenosesyndrome.org). The summer decline in Little Brown Bat capture rates in southwest Wisconsin is also consistent with trends at hibernation sites in Grant County, where individual counts of Little Brown Bats have declined over 99% since 2011 (J. Paul White, Wisconsin Department of Natural Resources, Madison, WI, unpubl. data). It is likely that the impact of WNS may lead to a restructuring of the bat community in southwest Wisconsin, as it has elsewhere (Thalken et al. 2018). In short, the Little Brown Bat—the species that was the most frequently captured species in my study and the species that has been considered the most abundant bat in Wisconsin by others (Jackson 1961, Long 2008)—is declining in Wisconsin. Whether the Little Brown Bat will experience local extinction in the midwest in the years ahead, an outcome predicted elsewhere in WNS-impacted regions (Frick et al. 2010a, Pettit and O’Keefe 2017), remains to be seen. Regardless, the current trends in population metrics for this species are sobering. Conclusions Specific information on the natural history of bats from Grant County, in southwest Wisconsin, are presented here for the first time. Much of the information provided here—on relative capture rates of bats from the region, reproductive phenology, and morphological metrics—is in alignment with results from other regions. The importance of regionally specific data is highlighted in this era of WNS, as bat communities change in response to this disease and species’ responses vary. Due to the long-term nature of this study, the impacts of WNS on our area bat populations are apparent. Specifically, relative capture rates are evidence that summer populations of the Little Brown Bat have declined. Such declines in population metrics are consistent with expectations of the effects of WNS on regional populations of affected species. The decline in population metrics of the Little Brown Bat in southwest Wisconsin, a species historically Northeastern Naturalist 180 J.J. Huebschman 2019 Vol. 26, No. 1 considered one of the most abundant species in Wisconsin, is ecologically significant. Monitoring of bat populations in southwest Wisconsin should continue in order to detect ongoing changes to this bat community. Acknowledgments This work would not have been possible without the critical help of UW-Platteville undergraduate students. The following students contributed to this research: Melissa Nickeletti (2006); Matt Willey (2007); Billy Abbott, Brittany Schultz, and Andy Stietz (2008); Kaley Bushman, Brittany Fritsch, and Sharri Valosek (2009); Rachel Allen, Brian Evanoff, and Sarah Lubin (2010); Caitlin Gorden, Carl Oppert, and Jennifer Trantow (2011); Tanner Ruechel and Christin Selle (2012); Josh Riley and Brittney Rogness (2013); Erin Holmes and Molly Lingel (2014); Katya Frank and Allison Wells (2015); Paige Ehrecke, Scout Harrison, and Cody Mitchem (2016); and Samantha Hoerner, Jacob Nottestad, and Kiara Zurow (2017). Colleagues from the Wisconsin Department of Natural Resources, including J. 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