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The discovery of a reproductive population of eastern small-footed bat, Myotis leibii, in southern Illinois using a novel survey method.


The eastern small-footed bat (Myotis leibii) is possibly one of the rarest, most poorly understood bats in North America. Its patchy distribution and small size (avg forearm = 32 mm and avg weight = 3-5 g) cause the species to be difficult to observe, leading to few published studies on the species (Best and Jennings, 1997; Johnson et al., 2011; O'Keefe and LaVoie, 2011). While most summer roosts are thought to occur in cracks and crevices of rocky outcrops and talus slopes, roost sites also have also been found in bridge expansion joints and other man-made structures (Best and Jennings, 1997; Johnson and Gates, 2008; Johnson et al., 2011; O'Keefe and LaVoie, 2011).

The range of Myotis leibii extends from New England down the Appalachian Mountains through North Carolina and across Missouri and Arkansas. Historical range maps include the southern portion of Illinois in the distribution of M. leibii (Best and Jennings, 1997); however, the closest published record of the species prior to 2005 was from Missouri 160 km away (Steffen et al., 2006). Most modern range maps do not include the state of Illinois (e.g., Whitaker and Hamilton, 1998; Bogart, 1999; Reid, 2006). The Illinois Natural History Survey lists M. leibii as a species of possible occurrence (Hofmann, 2008). Despite extensive mist-netting and hibernacula surveys across southern Illinois over the last decade (T. Carter, unpub. data) the only published record of eastern small-footed bats in Illinois was from a Nov. 2005 discovery of two individuals under a rock at the Fink Sandstone Barrens of Shawnee National Forest (SNF), Pope County, IL (Steffen et al., 2006). However, it is unclear if these individuals were migrants or a part of a reproductive population. Two additional records of male M. leibii from Pope Co., found within 10 km of the 2005 record, were transferred to The Field Museum, Chicago, IL in 1993 (Cat# 150639 & 150632). However, exact collection dates and additional details were not recorded for these specimens (Field Museum of Natural History, 2008).

Myotis leibii is a species of concern across much of its range with several states providing protection to the species (Harvey et al., 2011). In Jun. 2011, the U.S. Fish and Wildlife Service found that listing the eastern small-footed bat under the Endangered Species Act may be justified and requested information on the species in order to complete a 12 mo review (USFWS, 2011). In response, we initiated a survey for the species on the SNF to document the extent of a potential M. leibii population within the area.


Using satellite imagery, we identified 15 exposed rock outcrops located near the 2005 Myotis leibeii record at Fink Sandstone Barrens, SNF (Johnson and Pope Counties, IL; Fig. 1). Size of the outcrops varied greatly, but most were narrow (10-30 m wide). Each rock outcrop consisted of nearly level exposed bedrock with various amounts of loose rubble/rock debris scattered on top. Vegetative cover was sparse on the rock outcrops, consisting of scattered patches of shrubs and cedar trees (Juniperus virginiana). Between 25 Jul. and 16 Aug. 2011, one to five people searched each outcrop during the day by overturning all loose rocks and examining cracks within the exposed bedrock and below boulders. Search time varied greatly depending on amount of debris and size of outcrop (~15-90 min per person). When possible, we captured bats by hand to determine sex, age, and reproductive condition.


Twenty-nine Myotis leibii, were observed on eight of the 15 rock outcrops that we searched by hand (Table l; Fig. 1). Working together, five people observed 10 M. leibii over the course of 90 min at our most successful site, Fink Sandstone Barrens. Two adult females (1 post-lactating, 1 non-reproductive) were each discovered using the same roost as a juvenile. Other M. leibii were observed roosting singly or in small groups, up to five bats. The 10 bats captured by hand were primarily captured in the morning hours when bats were still in torpor. Bats were more alert and escaped as soon as rocks were overturned during later hours, presumably due to an increase in temperature. All roost sites were located within shallow gaps underneath loose rocks lying on exposed bedrock. No bats were able to be seen roosting within crevices in the bedrock or underneath large boulders. Myotis leibii were not located on rock outcrops that lacked loose rock scattered over the bedrock surface. One voucher specimen was submitted to The Field Museum, Chicago, Illinois.


Although the extent of Myotis leibii occurrence in southern Illinois is still poorly understood, this survey indicates that a resident breeding population occurs, at least locally, within the southern tip of the state (Johnson and Pope Counties). All bats were discovered roosting under overturned rocks; none were seen within crevices in the bedrock or under large boulders. However, Johnson et al. (2011) reported that many radio-tagged bats followed to crevices were not visible. Therefore, additional bats could have been roosting within crevices of the rock outcrops we searched, including outcrops on which no bats were found.

Still, the Myotis leibii population within southern Illinois may be small due to limited availability of typical roosting habitat across the landscape (i.e., tallus/shale slopes, rock outcrops, etc.). The only potential habitat appears to be small patches (often <1 ha) of sandstone/limestone glades, loess hill prairies, and barrens scattered in a narrow east- west band across SNF (Heikens and Robertson, 1995). However, the population could be larger and more expansive if individuals are using atypical roost sites throughout the Shawnee hills such as sandstone glade habitat or man-made structures (bridges, buildings, etc.) as observed in other regions (Hitchcock, 1955; Best and Jennings, 1997; O'Keefe and LaVoie, 2011). However, previous bridge surveys have not found any M. leibii within the area (Feldhamer et al., 2003).

We agree with Steffen et al. (2006) that previous mist-netting surveys may not have documented the species in Illinois because they have focused on monitoring the endangered Indiana bat (Myotis sodalis) in bottomland forest, while M. leibii probably prefer upland forest (Best and Jennings, 1997). Additionally, the short distances M. leibii are believed to travel between roosts (<1 km) and while foraging (0.8-3.2 km; Chenger, 2008; Johnson and Gates, 2008) make detection unlikely by surveys not conducted within close proximity to roost sites. Myotis leibii may have been overlooked in area hibernacula surveys due to the belief that they did not occur in the state (Steffen et al., 2006) or because they hibernate out of sight deep within crevices or under rubble on the cave floor (Martin et al., 1966; Best and Jennings, 1997). Furthermore, two potential hibernacula within 5 km of the roosts we documented have not been surveyed. If M. leibii only disperses small distances from hibernaculum (possibly <20 km; Hitchcock, 1955; Johnson and Gates, 2008) the species may not be present in the nearest surveyed hibernacula which are 15-30 km from the areas M. leibii were found. It is also likely that M. leibii hibernates deep within the cracks of the sandstone bluffs where they were found (Saugey et al., 1993).

Additional information on the ecology and distribution of this species is pertinent, especially if it becomes listed under the Endangered Species Act. While appropriate in some areas, mist-netting and hibernacula surveys may not be the most efficient survey method if populations are highly dispersed. For example, five people searching together for only 90 min yielded 10 Myotis leibii captures at one site. Furthermore, a single researcher can survey multiple potential roost sites in one day but is limited to one mist-net site. Therefore, we suggest future surveys for M. leibii should consider efforts to search for roosts under rocky debris. However, all roosts of M. leibii cannot be surveyed in this manner (i.e., talus slopes or cliffs) and the inclusion of multiple survey methods may be the most successful way to document the distribution of M. leibii.

Acknowledgments.--Funding was provided by the Shawnee National Forest. We thank B. Shimp, SNF, and M. McCann for their help in the field and the anonymous reviewers who contributed greatly to improving this manuscript.


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MICHAEL WHITBY (1), SCOTT BERGESON, TIMOTHY CARTER, AND STEPHANIE RUTAN, Department of Biology, Ball State University, Muncie, Indiana 47306; and ROD MCCLANAHAN, Wildlife Biologist, Shawnee National Forest, USFS, Vienna, Illinois 62995. Submitted 20 October 2011; accepted 11 May 2012.

TABLE 1.--Age, sex, and reproductive status of Myotis Libii discovered
in visual surveys of sandstone outcrops in Shawnee National Forest,
Illinois, USA 25 Jul.-16 Aug. 2011 (UNK indicates that bats were
unable to be examined in hand).

    Site                   Female-   Male-   Juvenile-   UNK    TOTAL
                            Adult    Adult     Male

1   Fink Sandstone           --       --        --         1       1
2   Fink Sandstone            2        1         1         6      10
3   Hunting Branch West      --       --        --         3       3
4   Jackson Falls West        1       --         1         5       7
5   Jackson Falls            --        1        --        --       1
6   Jackson Falls East       --       --        --         3       3
7   Parson's Ridge West      --        1         1         1       3
8   Parson's Ridge East      --        1        --        --       1
    TOTAL                     3        4         3        19      29
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Title Annotation:Notes and Discussion
Author:Whitby, Michael
Publication:The American Midland Naturalist
Article Type:Report
Geographic Code:1U3IL
Date:Jan 1, 2013
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