Ecology and management of the Indiana bat in Michigan.

ABSTRACT

The Indiana bat (Myotis sodalis) is one of two mammals on the federal list of endangered species that consistently breed in Michigan. Most Indiana bats from Michigan winter in southern Indiana or Kentucky, but a few hibernate at Tippy Dam in northern Lower Michigan; warm-season records (April-October), in contrast, exist for 12 counties in southern Lower Michigan. Births typically occur in mid-to-late June, and lactation lasts 3-5 weeks. Eighty-nine percent of adult females are reproductive (pregnant, lactating, or postlactating) , and 11% of all adults are male. We discovered 69 roost trees used by females and young in six different counties, and most species of tree are typical of lowlands, such as various ash (Fraxinus, 45%), maple (Acer, 36%), and elm (Ulmus, 12%). As a means of avoiding direct "take," resource managers often allow cutting of potential roost trees while Indiana bats are hibernating; however, we recommend that clusters of high-quality, potential roosts not be removed before verifying wheth er they are used by the bats.

INTRODUCTION

The Indiana bat (Myotis sodalis) is a small (7-10 g), insectivorous species that lives only in the eastern United States (Thomson 1982). During winter, most Indiana bats hibernate in mines or caves, primarily in Illinois, Indiana, Kentucky, and Missouri. In spring, these bats disperse from their hibernacula, with most animals, especially females, migrating 100-5 00 km northward to the northern parts of Illinois, Indiana, Ohio, and Missouri, as well as southern Michigan (Gardner and Cook 2002; Kurta and Murray 2002). Females in summer gather in small maternity colonies of less than 100 animals, whereas males typically lead a solitary life. Both males and females, however, usually roost under the exfoliating bark of dead trees (Gardner et al. 1991; Kurta et al. 2002).

The species was declared endangered in the United States under the Endangered Species Preservation Act of 1966, because of declining populations at known hibernacula and a perceived lack of critical habitat in winter (Clawson 2002). Initially biologists believed that declines were caused by human disturbance and/or alteration of microclimates at mines and caves that were used during hibernation, but despite protection of all major hibernacula, the number of Indiana bats continued to decrease. The ongoing decline suggested that this species also was experiencing problems on its summer range, perhaps related to habitat loss or use of pesticides (O'Shea and Clark 2002). Beginning in the 1990s, the plight of this bat received considerable attention from resource managers and environmentalists, and the species became known as the "spotted owl of the East," as disputes over its protection led to court-ordered shut-downs of logging on national forests from North Carolina to Missouri to Pennsylvania.

The Indiana bat is of particular concern to citizens of Michigan, because this bat is one of only two species of mammal on the federal list of endangered species that consistently breeds within the state. Although the first Indiana bat from Michigan was taken in the 1860s (Kurta et al. 1993), there were only 29 additional records prior to 1980 (Kurta 1980b). Eight bats were museum specimens collected between 1946 and 1974, five records represented animals that were banded in Kentucky and recovered in Michigan from 1963 to 1971, and 16 animals were mist-netted over streams in 1978 and 1979. Since 1979, however, we have captured over 100 additional Indiana bats in the state. The purpose of this paper is to synthesize information concerning the seasonal and geographic distribution of Indiana bats in Michigan, as well as their roosting requirements and reproductive events. Such information is essential for proper management of the species and to insure that continued alteration of the landscape does not impact su rvival of this endangered mammal on the northern edge of its range.

METHODS

Southern Lower Michigan

We extracted information from a previous report (Kurta 1980b) on Indiana bats in southern Lower Michigan and supplemented it with new data obtained by mist-netting and radiotracking since 1979 (e.g., Kurta et al. 1993, 1996, 2002). Fieldwork most often occurred between late May and mid-to-late August, although a few observations were made earlier or later. After locating a roost tree through radiotracking, we generally recorded the species of tree, diameter at breast height, height of tree, and height of the bats' exit, which we assumed approximated the height at which bats roosted. In addition, we estimated number of hours of sunlight striking the roosting area, using categories of low (0-5 h), medium ([greater than or equal to]5 but <10 h), and high (10 h), and the amount of exfoliating bark present, also using categories of low (<10%), medium ([greater than or equal to]10 but <25%), and high (25%), following Gardner et al. (1991). Not all parameters were measured for every tree, generally because of proble ms with landowner permission or other logistical difficulties. Pregnancy of captured animals was determined by palpation, and lactation was determined by condition of the nipples and ability to express milk (Racey 1988). Age (juvenile vs. adult) was assigned based on degree of ossification of the phalangeal epiphyses (Anthony 1988).

Tippy Dam

In addition to animals summering in southern Lower Michigan, we also captured Indiana bats that were using the spillway at Tippy Dam for autumn swarming and winter hibernation (Kurta and Teramino 1994; Kurta et al. 1997). Tippy Dam is a hydroelectric facility near Wellston, in Manistee Co., in the northern Lower Peninsula. The spillway is the only significant hibernaculum for bats in the Lower Peninsula, sheltering about 19,000 hibernating individuals. Most (>99%) are little brown bats (Myotis lucifugus) and northern bats (Myotis septentrionalis), although eastern pipistrelles (Pipistrellus subflavus) and Indiana bats are also present (Kurta et al. 1997). During swarming, we captured bats with a harp trap (Kunz and Kurta 1988), and during hibernation, they were taken by hand or with a long-handled net. Aging bats through phalangeal ossification often becomes unreliable in late summer, and we did not attempt to do so at Tippy Dam.

Marking Bats

Beginning in 1994, most Indiana bats were banded (Kurta and Murray 2002), whereas those captured before 1994 were punch-marked (Bonaccorso and Smythe 1972) for future recognition. Punch-marking allowed recognition of individuals for only a few weeks, whereas banding provided an ability to distinguish individuals over multiple years. Our bands were inscribed with a unique four-digit number and the letters "EMU YPSI MI."

RESULTS AND DISCUSSION

Tippy Dam

To date, we have captured 15 Indiana bats, eight females and seven males, at Tippy Dam. Eleven Indiana bats were found between November and March during hibernation, and the other four were caught during swarming in late August or September. The internal shape of the spillway prevented us from approaching most hibernating bats (Kurta et al. 1997), and identification of such tiny mammals from a distance was not practicable. Consequently, it was not possible to count the Indiana bats that hibernated there, although Kurta et al. (1997) estimated that the maximum number of Indiana bats was 65. Our subsequent visits to the dam reinforced the original conclusion that the population of Indiana bats at Tippy Dam was very small. Indiana bats, nevertheless, consistently have been found in the spillway, with at least one individual encountered in seven of eight years (1994-2001) since the species was discovered there on 25 February 1994.

Although the first Indiana bat located at the dam was not banded, the other 14 individuals were, and two of these were recaptured in subsequent years. A male initially caught on 24 August 1995 was recaptured on 13 September 1997 and again on 11 September 1999, whereas a female banded on 18 March 1995 was seen again on 14 February 1998. These recoveries, along with the consistent presence of Indiana bats over an eight-year period, suggested that Tippy Dam sheltered an established population and that our initial captures were not simply wayward animals that accidentally located the hollow spillway, only to perish or move on the next year.

Where do Indiana bats from Tippy Dam spend the summer? A mist-netting survey in 1985 at 46 sites, including many netting sites within 150 km of the dam, failed to capture any Indiana bats (Kurta et al. 1989). In addition, a survey during 1999-2000 at 27 sites in the Manistee National Forest, which surrounds Tippy Dam, did not yield an Indiana bat (Kurta 2000). This lack of success could indicate that the bats summer far from the dam; however, the sampling effort in both studies was not sufficient to rule out presence of an uncommon species within such large geographic areas.

Indiana bats hibernating at Tippy Dam, like bats at other sites, could migrate in any direction for summer. The Indiana bat, however, is essentially a southern species, and those hibernating at Tippy Dam are the northernmost representatives of the species in the Midwest. Consequently, we hypothesize that Indiana bats from Tippy Dam will summer near the coast of Lake Michigan and suggest that future surveys be concentrated there. The lake has a moderating effect on local climate that extends only a short distance, perhaps 30-50 km from the coast, and within this narrow zone, there exists a thermal environment very similar to that of southern Lower Michigan (Keen 1993), where we commonly find these bats. For example, the growing season (number of days between freezing temperatures in spring and autumn) is similar between Manistee, on the coast only 30 km west of the dam, and Jackson, which is more than 225 km farther south. Migrating only 50-150 km away from the lake would yield significantly cooler temperature s that could reduce food supplies (flying insects) in spring, forcing the bats into prolonged torpor with resulting delays in embryonic and! or juvenile development (Humphrey et al. 1977; Racey 1982).

Alternatively, Indiana bars at the dam may migrate more than 190 km to Lansing or farther south for warm temperatures, where they would mingle with Indiana bats that are known to hibernate in Indiana and Kentucky (Kurta 1980b; Kurta and Murray 2002). This distance (190 km) is well within the migratory abilities of the species, and we already know that even Indiana bats from the same summer colony do not necessarily hibernate in the same location (Kurta and Murray 2002). We question, however, why the bats would fly such long distances when suitable climate arid unoccupied habitats are available only a short distance from Tippy Dam.

Geographic Distribution in Southern Lower Michigan

Kurta (1980b) concluded that the Indiana bat was a widespread summer resident of southern Lower Michigan, and our new information (Figure 1) supports that statement. Records of the Indiana bat currently exist for 12 southern counties, an increase of three counties since 1980, with the addition of Branch, Jackson, and Lenawee counties. Since 1980, Indiana bats also have been captured at new localities in Hillsdale, St. Joseph, and Washtenaw counties, as well as at a previously discovered site in Eaton Co.

Indiana bats migrate up to 532 km from hibernacula to summer quarters (Gardner and Cook 2002; Kurta and Murray 2002). Based on this distance, location of hibernacula in Indiana and Kentucky (Gardner and Cook 2002; United States Fish and Wildlife Service 1996), and capture localities in Michigan (Figure 1), we believe that Indiana bats could occur anywhere that suitable habitat exists within the southern three rows of counties in Michigan and perhaps farther north, especially on the western side of the state. Although records of the Indiana bat do not exist for seven of 19 counties in the southern three tiers of counties, we attribute these gaps in distribution to lack of fieldwork by biologists trained to capture bats. For example, to our knowledge, no one has ever attempted to capture foraging bats, of any species, in Macomb and Oakland counties. In addition, only limited mist-netting has taken place in Berrien, Cass, and Van Buren counties (Kurta 1980a), with none occurring in the past 22 years.

Seasonal Distribution in Southern Lower Michigan

The earliest seasonal record of an Indiana bat from southern Lower Michigan is an adult male found in Washtenaw Co. on 11 May 1965 (Kurta 1980b), although there are eight other records from May as well. In addition, as part of a long-term study of a maternity colony in Eaton Co. (Viele 1994; Viele et al. 2002), biologists observed evening emergence of bats from trees to which Indiana bats had been radiotracked during the previous year. Bats that were presumed to be Indiana bats left these trees as early as the night of 28 April. Most female Indiana bats leave southern hibernacula during early and mid-April (Cope and Humphrey 1977), and only 9 days are needed to travel from caves in Kentucky to southern Michigan (Davis 1964; Kurta 1980b). Consequently, Indiana bats from southern hibernacula probably begin arriving in Michigan no later than mid-to-late April, and this timing is supported by the observation from Eaton Co. (Viele 1994; Viele et al. 2002).

The latest seasonal record is a female found in Lansing on 11 October 1974 (Kurta 1980b). In addition, bats left known roost trees in Eaton Co. as late as 10 September 1991 and 12 September 1992, and there also are three older records from September (Kurta 1980b). Mating by Indiana bats occurs at hibernacula primarily in September and early October (Barbour and Davis 1969; Cope and Humphrey 1977), and any bat still in southern Lower Michigan is missing such opportunities. However, many juveniles of temperate species of bat do not breed in their first autumn (Gustafson 1975; Racey and Entwistle 2000; Schowalter et al. 1979), and they typically arrive at hibernacula later than do adults (Thomas et al. 1979). Consequently, the October record and perhaps the September records may represent individuals that were born that summer. In any event, October seems late for these bats to remain in southern Lower Michigan, whether they are juveniles or adults, because nighttime temperatures frequently fall below 10[degrees ]C during October. Such low temperatures greatly reduce the number of flying insects (food), and it is not clear why a healthy bat would delay its migration and remain in southern Michigan under such circumstances.

Presence of Adult Males in Southern Lower Michigan

Data on age and reproductive condition are not available for Indiana bats taken in Michigan prior to 1978. However, since 1977, we have captured 87 Indiana bats in southern Lower Michigan--64 adult females, 8 adult males, and 15 juveniles. Although males typically remain near hibernacula during summer (Gardner and Cook 2002; Whitaker and Brack 2002), 11% of our adult captures are males, indicating that substantial numbers of both sexes migrate over 400 km each year (Kurta and Murray 2002). Our value of 11% probably underestimates the proportion of adult males in the summer population, because our netting preferentially occurs near maternity roosts (Kurta et al. 1996,2002), and male Indiana bats, as in many other species, often do not roost with females during the maternity period (Gardner et al. 1991).

Reproduction in Southern Lower Michigan

Fifteen adult females were recaptured one or more times after initial banding, so the 64 adult females were caught a total of 84 times. For determining the timing of reproductive events, we treated each capture as an independent event because we had no control over which individuals were recaptured, or at what time of year, and because banding and recapture usually occurred in different years. Pregnant Indiana bats were caught on 23 occasions; lactating females, 32 times; and postlactating individuals, 11 times. Eleven bats caught in spring were not palpably pregnant, and seven adult females netted in summer appeared nonreproductive.

Indiana bats become pregnant soon after leaving hibernation through the process of delayed fertilization (Guthrie 1933) and presumably enter southern Michigan already pregnant. Palpation can not reliably detect an embryo during the first half of pregnancy, and palpably pregnant bats were not identified until 22 May (Figure 2). The last pregnant bat was detected on 3 July, but juveniles began entering the volant population as early as 15 July. Lactating females, in contrast, were captured as early as 21 June and as late as 25 July. Although Kurta (1980b) reported a lactating female on 15 August, a review of the original field notes indicated that that statement was an error. Hence, most births probably occurred in mid-to-late June, with lactation occurring throughout July and lasting 3-5 weeks. Timing of reproductive events in Michigan was essentially identical to that in south-central Indiana (Humphrey et al. 1977), despite longer migrations and cooler ambient temperatures for northern populations.

Knowing the proportion of the population that is reproducing is important for management of any endangered species, especially one, such as the Indiana bat, in which females produce only a single young each year. We limited our analysis to bats captured after 15 June to eliminate not-palpably-pregnant females, which may or may not have been pregnant. Using this restricted sample, we calculated that 89% of 63 captures of adult females represented reproductive individuals (pregnant, lactating or postlactating).

Reproductive rates of the closely related little brown bat often exceed 95%, but location and stochastic events, such as amount of rainfall and temperature, can lead to lower rates (Humphrey and Cope 1976; Grindal et al. 1992). Although our estimate for Indiana bats is within the range of observed values for its non-endangered congener, there are no comparable data for Indiana bats from other parts of the country. This is unfortunate, because there are large regional differences in the decline of Indiana bats, as indicated by counts at hibernacula. Populations in Missouri, for example, have decreased by 79% since 1980, whereas those hibernating in Indiana increased slightly (Clawson 2002). Knowing whether declines at various hibernacula corresponded with reduced rates of reproduction on the summer range could be helpful in determining the cause of the decline in population size. We encourage investigators in other states to determine reproductive rates by analyzing their accumulated data for comparison.

Roost Trees Used by Maternity Colonies

Radiotracking adult females or juveniles led to discovery of 69 roost trees that were used during the maternity season (Table 1). Most roosts were found in Eaton (Kurta eta1. 1993,1996) and in Jackson and Washtenaw (Kurta et al. 2002) counties, where we performed concentrated, multi-year studies. Nevertheless, roost trees also were located in Branch, Lenawee, and St. Joseph counties.

Indiana bats in Michigan most often roost under the loose bark of dead trees, although narrow crevices (as opposed to tree hollows or woodpecker cavities) are used occasionally (Table 1). Peeling bark usually covers 25% or more of the tree, although amount of exfoliating bark on roost trees is similar to that of nearby, randomly selected trees (Kurta et al. 1996, 2002). A typical roost tree has a diameter of 41 cm (Table 1) and is larger than neighboring trees that are available to the bats (Kurta et al. 1996, 2002). Average height of a tree is 21 m, and on average, bats roost halfway up the tree, as indicated by the exit height. Most roosts receive 10 or more hours of sun each day.

Roost trees in Michigan belonged to at least eight species, and most were typical of lowland areas (Table 1), such as various ash (Fraxinus, 45%), maple (Acer, 36%), and elm (Ulmus, 12%). Although Indiana bats in southern states (Callahan et al. 1997; Gardner et al. 1991) frequently used oaks (Quercus) and shagbark hickories (Carya ovata) , these species were not important in Michigan. We never radiotracked an adult female or juvenile to an oak, and we located only three shagbark hickories that were used as roosts. Each shagbark hickory, however, was a heavily shaded, living tree, and each was found by radiotracking a postlactating female--one bat in Jackson Co. and another in St. Joseph Co. Maximum number of bats at each hickory was only 2-5, whereas focal roost trees (sensu O'Donnell 2000) used by pregnant and lactating Indiana bats typically sheltered 15-50 bats in Michigan (Kurta et al. 2002).

Although Callahan et al. (1997) call for preservation of oak-hickory forests as a means of maintaining roosts for maternity colonies of Indiana bats, current data do not support this tactic as a management strategy in Michigan. The difference between Missouri and Michigan, however, may be due partly to a difference in availability of various trees. Elm-ash-cottonwood associations, for example, are typical of lowland forests in many parts of southern Michigan, and they are more prevalent in counties with records of reproductively active Indiana bats in Michigan than in any other state (G. Gardner in litt.; United States Fish and Wildlife Service 1996). On the other hand, there may be regional differences in roost-site selection, with Indiana bats in Michigan actively selecting lowland sites (Kurta et al. 2002). We suggest that biologists locate and study intensively (e.g., Kurta et al. 1996, 2002) new maternity colonies in different areas of Michigan, to determine whether this apparent preference for lowlands and lowland species of trees is consistent across the southern part of the state and not an artifact of our sampling or availability of different habitats.

Such studies are urgently needed, especially in light of the introduction of the emerald ash borer (Agrilus planipennis). This Asian insect was first identified in North America in July 2002, although it likely arrived a few years before that (McCullough and Roberts 2002). In North America, this beetle currently is known only from southeastern Michigan and adjacent Ontario. The emerald ash borer has decimated local populations of ash trees (including green and black ash), and the infestation likely will spread soon to other parts of the Indiana bat's range. Although actions of this beetle temporarily may increase available roosting habitat for Indiana bats, by rapidly increasing the number of dead trees, the long-term effects are uncertain. Large-diameter elms that could be used as roosts are already uncommon in southern Michigan, due to Dutch elm disease (Barnes 1976; Barnes and Wagner 1981), and the emerald ash borer may cause a similar long-term decline in availability of large-diameter ash.

Roosts of Adult Males in Southern Lower Michigan

We also located nine roost trees used by four adult males (Table 2). Two roosts were identified when male Indiana bats were captured in nets placed near maternity roosts, but the other seven trees were found by radiotracking three males. All males roosted under exfoliating bark, and as with the females, most trees were dead elm, ash, or maple. In addition, one male was radiotracked to a living red oak (Quercus rubra), where the bat rested under bark, on a dead branch, near the trunk; the branch, which was only 10 cm in diameter, was below the thick canopy, and no direct sunlight struck the roosting site.

Cutting Potential Roost Trees

The U. S. Fish and Wildlife Service often allows potential roost trees to be cut after Indiana bats leave for hibernation in order to make way for developments such as new bridges, highways, and housing projects. This policy understandably is intended to allow human developments to proceed while preventing direct "take" of Indiana bats. This practice, however, should be limited, because it destroys potential roost trees without establishing whether they actually are used by Indiana bats, which may leave the bats with no shelter when they return in spring in an energetically stressed condition. Upon returning, the bats have just completed 6-7 months of hibernation and an extensive migration, and they arrive already pregnant and at a time when air temperatures are low and food (flying insects) is scarce. Excessive precipitation and/or colder-than-average temperatures drastically reduce reproductive success of temperate bats (Grindal et al. 1992; Lewis 1993), and such negative effects likely would occur even dur ing normal weather if Indiana bats do not have adequate shelter.

We acknowledge that a colony of Indiana bats uses a large number of trees each year (Callahan et al. 1997; Kurta et al. 1996, 2002) and that some roost trees fall over or otherwise become unsuitable for bats through natural means on a regular basis (Gardner et al. 1991; Kurta 1994; Kurta and Foster 1995; Kurta et al. 2002). Roost trees, however, are clustered, rather than randomly spread throughout the landscape (Kurta et al. 1996, 2002), and our concern is that a single new shopping center or highway re-alignment could simultaneously destroy all high-quality roosts used by a particular colony. Although cutting of isolated trees used as alternate roosts may do little harm, we recommend that clusters of high-quality, potential roosts (loose bark, unimpeded access, high solar exposure, etc.) not be removed until it is shown that they are not actually used by Indiana bats.

If trees that are suitable as roosts must be removed, we suggest that cutting be limited to a period between 1 November and 31 March of each year. The population of hibernating bats at Tippy Dam reaches winter levels by mid-October and remains high until mid-April (Kurta et al. 1997); hence, any Indiana bats that hibernate there would not be affected directly by tree-removal during that time. In addition, a no-cut period from 1 April to 31 October conservatively brackets all known seasonal observations of Indiana bats in southern Lower Michigan and would ensure that these animals are protected during the reproductive season. Rangewide, the population of Indiana bats has decreased by 57% since 1960 (Clawson 2002), and only through continued research and enlightened management will we reverse this trend.

ACKNOWLEDGEMENTS

Much of the previously unpublished data on Indiana bats in Michigan was gathered by former graduate students at Eastern Michigan University: R. Foster, S. Murray, J. Teramino, A. Tibbels, D. Viele, and K. Williams. Undergraduates that provided invaluable assistance included J. Caryl, S. Gaitens, J. Kappler, C. King, A. Kuehn, M. Lucas, M. McGuire, W. Monroe, and J. Werner. Primary funding for fieldwork on Indiana bats in Michigan from 1991 to 2002 was provided by grants to AK from the Nongame Program of the Michigan

Department of Natural Resources. Additional support came from grants/ contracts to AK from Consumers Energy Company, the Graduate School of Eastern Michigan University, The Nature Conservancy (Michigan Chapter), United States Fish and Wildlife Service (East Lansing Office), United States Forest Service (Huron-Manistee National Forests), and Wildlife Forever. Work on Indiana bats by our laboratory also was aided by grants from Bar Conservation International to S. Murray, from Sigma Xi to A. Tibbels, and from the American Society of Mammalogists and Theodore Roosevelt Fund of the American Museum of Natural History to K. Williams. D. Battigge, M. DeCapita, P. Myers, and D. Viele commented on the manuscript. M. DeCapita provided information on the emerald ash borer

[FIGURE 2 OMITTED]

TABLE 1

Roost trees used by adult females and/or young Indiana bats in southern
Lower Michigan.

                                               Number      Number
          Species                    Number   of living   of roosts
                                    of trees   vs dead      under
                                                trees     bark vs.
                                                         in crevices

Green ash (Fraxinus pennsylvanica)     27       1/26        26/1
Silver maple (Acer saccharinum)        11       0/11        11/0
Unidentified maple (Acer sp.)           9        0/9         9/0
American elm (Ulmus americana)          7        0/7         7/0
Blak ash (Fraxinus nigra)               4        0/4         4/0
Red maple (Acer rubrum)                 3        0/3         1/2
Shagbark hickory (Carya ovata)          3        3/0         3/0
Cottonwood (Populus deltoides)          1        0/1         0/1
Slippery elm (Ulmus rubra)              1        0/1         0/1
Unidentified                            1        0/1         1/0
Total                                  69       4/65        64/5

                                          Diameter
          Species                         (cm) (1)
                                         at breast
                                           height


Green ash (Fraxinus pennsylvanica)   39 [+ or -] 1 (27)
Silver maple (Acer saccharinum)     47 [+ or -] 11 (11)
Unidentified maple (Acer sp.)        48 [+ or -] 4 (8)
American elm (Ulmus americana)       36 [+ or -] 4 (7)
Blak ash (Fraxinus nigra)            25 [+ or -] 3 (4)
Red maple (Acer rubrum)              41 [+ or -] 3 (3)
Shagbark hickory (Carya ovata)       51 [+ or -] 6 (3)
Cottonwood (Populus deltoides)               36
Slippery elm (Ulmus rubra)                   34
Unidentified                                 42
Total                                41 [+ or -] 2 (68)


          Species                        Height of
                                        tree (m) (1)



Green ash (Fraxinus pennsylvanica)  24 [+ or -] 2 (27)
Silver maple (Acer saccharinum)     18 [+ or -] 2 (11)
Unidentified maple (Acer sp.)        23 [+ or -] 2 (9)
American elm (Ulmus americana)       16 [+ or -] 2 (5)
Blak ash (Fraxinus nigra)            14 [+ or -] 1 (4)
Red maple (Acer rubrum)              23 [+ or -] 2 (3)
Shagbark hickory (Carya ovata)                  31 (1)
Cottonwood (Populus deltoides)                       9
Slippery elm (Ulmus rubra)                           9
Unidentified
Total                                21 [+ or -] 1 (64)


          Species                         Height of
                                        of exit (m) (1)



Green ash (Fraxinus pennsylvanica)   10 [+ or -] 1 (25)
Silver maple (Acer saccharinum)      10 [+ or -] 1 (10)
Unidentified maple (Acer sp.)         12 [+ or -] 2 (9)
American elm (Ulmus americana)         6 [+ or -] 1 (6)
Blak ash (Fraxinus nigra)            6 [+ or -] 0.3 (4)
Red maple (Acer rubrum)               13 [+ or -] 1 (2)
Shagbark hickory (Carya ovata)
Cottonwood (Populus deltoides)                        8
Slippery elm (Ulmus rubra)                            9
Unidentified
Total                                10 [+ or -] 1 (61)

                                       Number of          Number of
          Species                      trees with         trees with
                                      high, medium      high, medium,
                                      low, or zero          or low
                                    peeling bark (2)  solar exposure (3)

Green ash (Fraxinus pennsylvanica)    15, 8, 2, 0          25, 1, 1
Silver maple (Acer saccharinum)        4, 2, 5, 0           5, 2, 2
Unidentified maple (Acer sp.)          6, 2, 2, 0           7, 2, 0
American elm (Ulmus americana)         5, 0, 1, 0           2, 3, 0
Blak ash (Fraxinus nigra)              1, 2, 1, 0           0, 4, 0
Red maple (Acer rubrum)                0, 2, 0, 1           2, 1, 0
Shagbark hickory (Carya ovata)         3, 0, 0, 0           0, 1, 2
Cottonwood (Populus deltoides)         0, 1, 0, 0           1, 0, 0
Slippery elm (Ulmus rubra)             0, 0, 0, 1           0, 1, 0
Unidentified                           0, 1, 0, 0           1, 0, 0
Total                               34, 19, 11, 2         42, 15, 4

(1)Mean [+ or -] standard error n.

(2)Rating follows Gardner et al. (1991). High means that [greater than
or equal to]25% of trunk covered by peeling bark; medium, [greater than
or equal to]10 but <25% of trunk covered; low, < 10% covered.

(3)High means [greater than or equal to]10 h of exposure; medium

[greater than or equal to]10 h; low, <5 h.
TABLE 2

Roost trees used by adult male Indiana bats in southern Lower Michigan.

Species              Diameter                Height
                  at breast (cm)          of trees (m)


American elm            20                     12
American elm            16                      9
Black ash (3)           17                     16
Black ash (3)           24                     16
Black ash (3)           26                     13
Green ash               22                     20
Green ash (3)           52                     47
Red Oak                 52                     31
Silver maple            95                     31
Mean           36 [+ or -] 9 (9) (4)  21 [+ or -] 4 (9) (4)

Species               Height           Amount       Amount
                   of exit (m)       of peeling    of solar
                                      bark (1)   exposure (2)

American elm             4              High
American elm             3             Medium
Black ash (3)            5             Medium       Medium
Black ash (3)            5              Low         Medium
Black ash (3)           10             Medium       Medium
Green ash               15             Medium        High
Green ash (3)           12              High         High
Red Oak                 13              Low          Low
Silver maple            13              High
Mean           9 [+ or -] 2 (9) (4)

(1)Rating follows Gardner et al. (1991). High means that [greater than
or equal to]25% of trunk covered by peeling bark; medium, [greater than
or equal to]10 but <25% of trunk covered; low, <10% covered.

(2)High means [greater than or equal to]10 h of exposure; medium,
[greater than or equal to]5 but <10 h; low, <5 h.

(3)Trees initially located by radiotracking adult females.

(4)Mean [+ or -] standard error (n).

REFERENCES

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