Proceedings of the Indiana Academy of Science

Proceedings of the Indiana Academy of Science J27 (1992) Volume 101 p. 127-134 SEASONAL ACTIVITY OF BATS AT COPPERHEAD CAVE John O. Whitaker, Jr. and Leslie J. Rissler Department of Life Sciences Indiana State University Terre Haute, Indiana 47809 Abstract: Copperhead Cave is an abandoned mine in Vermillion County, Indiana, serving as both ahibernaculum and aswarming area for northern bats (Myotis septentrionalis), little brown bats (M. lucifugus), and eastern pipistrelles {Pipistrellus subflavus). Adouble-frame harp trap was used to document bat activity at the mouth of the mine on aweekly basis from the fall of 1989 to the spring of 1991. Most of the trapped bats were banded and released. Little brown bats of both sexes emerged gradually from hibernation between 14 March and 19 May 1990 and between 15 March and 1May 1991. In contrast, northern bats emerged in much larger numbers between 9 March and 27 April 1990 and between 21 February and 22 April 1991. The mine served as a swarming area from the end of July to the end of October for both species of Myotis and through the first week of October for the pipistrelles. The pipistrelles exhibited almost no winter activity (flight). However, the little brown bats and the northern bats were active at the mine entrance throughout the winter. Turnover in the bat populations of this mine is quite high, as indicated by the low number of banded bats recovered: 336 of 1733 (19.4%) individuals of Myotis lucifugus; 174 of 2090 (8.3%) individuals of M. septentrionalis; and 100 of 546 (18.3%) individuals of Pipistrellus subflavus. INTRODUCTION Copperhead Cave is an abandoned clay mine in abluff 1km west of the Wabash River and 1.5 km west of Montezuma in Vermillion County, Indiana. The mine is about 120 km northwest of the edge of the unglaciated cave country of southern Indiana, and it represents an artificial cave in an area where no natural caves exist. We were informed that the mine served as ahibernaculum for bats, and initial monitoring indicated that the mine was used in other seasons as well. Regular monitoring of the mine entrance was initiated to determine: 1. The species, number, and sex of the bats using the mine; 2. The seasonal use of the mine; 3. The uses to which the mine was put; 4. The dates of entrance into and exit from hibernation; 5. The size of the bat population; and 6. Whether or not astable bat population used the mine for extended periods of time, or if significant population turnover occurred. MATERIALS AND METHODS Adouble frame harp trap was used to sample bats flying at the entrance to the mine. Monitoring started in September 1989 and was to be terminated for the season on 30 October, because we assumed that bat activity would essentially cease by that time. However, to verify that little or no winter activity occurred, the trap was placed at the mine 128 ZooLOGY:Whitaker and Rissier Vol. 101 (1992) Table 1.Summary of information on the bats taken in atrap at the entrance to Copperhead Cave. Date M.t'ucifugus M. septentrionalis Pipistrellus male female male female male female 1989 Sept 19 110 14 41 27 43 22 100 10 310 6 26 62 19 710 34 30 67 710 18 25 Oct 340 11 117 10 24 11 16 21 23 15 13 21 564 38 32 17 31 571 1 20 92421 24 72 41 12 1 28 8 3 28 82 30 7415 6 1990 Jan 16 9312 23 3412 27 2 2 2 Feb 311 8736511 17 1 23 Mar 31521 93112 41 14 3 3 61 6 17 315 1 24 121 31 31 570 44 Apr 432 32 71437 62 1 11 4510 10 17 37919 27 77912 8 May 6213 94124 12 2211 19 244 26 13 3 Vol. 101(1992) Indiana Academy of Sen2NCE 129 Date M. ihicifiigus Mseptentrionalis Pipistirellus male female male female male female June 23 3 15 278 21 23 175 1 29 2 35 2 30 357 1 July 1232 1 2321 2 36119 3 4320 10 5717 6 6671 10 117 17 219 25 815 8 1 31 8331 11 5 2 Aug 79731 15 22 23 66 56 63 20 42 37 35 52 22 25 47 46 82 89 33 15 Sept 244 25 48 55 45 947 12 12 34 84 13 40 918 17 26 21 53 17 15 28 1 26 36 933 49 49 Oct 512 625 37 13 12 10 112 81 19 11 110 1 29 2113 6 Nov 84I21 15 1242 20 1348 30 142 Dec 8112 16 123 21 114 1991 Jan 2 112 10 332 18 2 25 21 130 ZooLOGY:Whitaker and Rissler Vol. 101 (1992) Date M.ilucifugus M. septentrionalis Pipistrellus male female male female male female Feb 2312 81 17 312 21 1310 28 34713 Mar 3165 149 7684 86 7112 2 15 410 713 22 212 5 29 15 5632 Apr 51130 10 22 4411 811 May 12288 9145 entrance on 21 November 1989, left in place, and checked daily through early December. After early December, the trap was checked sporadically. Through 9January 1990, a total of 63 bats was taken in this untended trap: 22 in November, 22 in December, and 19 in January. Included were 32 little brown bats, 29 northern bats, and 2pipistrelles. Much more winter activity occurred than had been anticipated. Therefore, starting on 16 January 1990, the trap was tended approximately one night per week until 9May 1991 (Table 1). In addition, an assessment of the bats hibernating in the mine was made on 23 February 1988, and similar assessments were made on 14 January 1989, 27/29 December 1989, and 3March 1991 (Table 2). Nearly all the bats taken in the trap and nearly all of those found in hibernation during the later two assessments were banded (plastic numbered bands from National Band and Tag Co, Newport, Kentucky). The bands remained on the bats quite well, but the numbers often become difficult to read within ayear or two. Four thousand, three hundred sixty-nine bats were banded, and 610 were recaptured at Copperhead Cave. RESULTS Bats use this mine year round (Table 1), although the amount of use varies seasonally. Decreased activity was encountered at the mine entrance from November through February and from early in May through the first week in June. The majority of bats encountered belonged to three species: the little brown bat, Myotis lucifugus, the northern bat, Myotis septentrionalis, and the pipistrelle, Pipistrellus subflavus. All three species swarm there in the fall, presumably for mating purposes, and all three also hibernate in the mine. Afew bats of two other species were also taken: seven Indiana bats {Myotis sodalis) and five big brown bats (Eptesicus fuscus). These bats will not be discussed further. Of particular interest was the fact that northern and little brown bats were active all winter at this mine. Increased activity occurred on warmer nights (Whitaker and Rissler, 1992). There was little winter activity by pipistrelles. The bats entering and leaving the Vol. 101 (1992) Indiana Academy of Science 131 Table 2. Bats in hibernation in Copperhead Cave. Date M. lucifugus M. septentrionalis Pipistrellus male female male female male female Feb. 23, 1988 111* 201* Jan. 14, 1989 106* 113* Dec. 27/29, 1989 85 48 47 45 March 3, 1991 165 149 7684 86 Bats were counted without removing them from the wall; thus, information on sex is not available. mine in midwinter do not feed even on warm nights, when insects are flying (Whitaker and Rissler, 1992). Some of the winter flights may reflect movements between hibernacula. However, some of the flying may occur because the bats are simply flying outside rather than inside during normal winter awakenings from hibernation (Cockrum, 1956; Menaker, 1964; Mumford, 1958). The total number of bats taken in 1990 and 1991 during the winter trapping sessions included: 27 northern bats and 10 little brown bats in December; 15 northern bats and 20 little brown bats in January; and 47 northern bats and 30 little brown bats in February. Only three pipistrelles were taken during the winter trapping sessions. Myotis lucifugus. Myotis lucifugus usually hibernates in caves, but this mine provides acave-like environment in an area with no caves. The mine served as ahibernaculum for the following minimum number of little brown bats on the following dates: 111on 23 February 1988; 72 on 14 January 1989; 133 on 27/29 December 1989; and 314 on 3 March 1991. No major peak of spring emergence activity by little brown bats was observed in either 1990 or 1991. The relatively small number of bats present probably emerged rather gradually from March through May. These data correlate fairly well with data on the buildup in amaternity colony of this species at Brazil, Clay County, Indiana. At Brazil, emergence started gradually in late March and was largely complete by late April (Ronald Davis, unpublished data). Copperhead Cave did not serve as amajor bachelor quarters for this species in the summer, as there was relatively little activity during June and July 1990. Between two to eight bats, including only three females, were taken each night from 1June to 25 July. On 31 July, eight males and three females were taken, followed by seven females and nine males on 7August 1990. Thus, the end of July and early August appear to mark the beginning of swarming for this species. These dates correlate quite well with adecrease in the summer population in the colony at Brazil in Clay County, where the number of bats present dropped off drastically beginning in early August. Swarming tapered off in October, with swarming by females decreasing sooner than that by males (10 October versus 17 October in 1990; 5October versus 19 October in 1991). Apparently, the bats move gradually to their swarming areas and then gradually into hibernation. Some of the bats hibernate at Copperhead Cave, but most move elsewhere, as indicated by the low number of banded bats found in hibernation. Prior to 3March 1991, atotal of 1470 little brown bats had been banded in or at the entrance to Copperhead Cave, whereas on 3March, only 72 banded little brown bats were found hibernating there. This number represents only 4.9% of the total number of bats banded. Several of the bats banded at Copperhead Cave were found hibernating during the winter of 1990-91 about 100 km to the southwest in 132 ZooLOGY:Whitaker and Rissler Vol. 101 (1992) Table 3. The total number of bats banded at Copperhead Cave. Species Male Female Unknown M. lucifugus 1234 491 8 M. septentrionalis 1431 652 7 Pipistrellus 325 219 2 Eptesicus 41 M. sodalis 43 Ray's and Clyfty Caves in the Lawrence County area. Myotis septentrionalis. Copperhead Cave apparently serves as ahibernaculum for northern bats, although not many individuals were found in hibernation. Three lines of evidence indicate that the mine is ahibernaculum: the (1) number of northern bats that entered the cave in fall; the (2) number that emerged in winter and spring; and the (3) bats found hibernating in tiny cracks in winter. The numerous cracks in this mine must serve as winter quarters for hundreds of northern bats, but finding them was very difficult in these cracks. On relatively warm spring nights, when northern bats were emerging from the mine, numerous individuals were found exiting from the cracks (e.g., twelve were observed on 15 March 1991). Northern bats emerge from hibernation early in the season. Large numbers exited from the mine on nights when the temperature approached 10° Cfrom the second week of March through April each year (Table 1). The modal exodus time for males was approximately one week ahead of that for females. An attempt was made to estimate the number of northern bats using Copperhead Cave in spring. Sampling times averaged 7.5 hours or 0.625 of the dark period at that time of year. To determine if banded bats might be reentering the mine or if bat activity might taper off after our normal sampling period ended, bats were trapped throughout the night on two separate occasions. The results indicated that bat activity continued all night and that individuals seen earlier did not generally return to the mine after our normal sampling period ended. The emergence of northern bats in 1990 started about 9March and lasted through 17 April, atotal of 40 nights. Samples were collected on ten of these nights. The average number of northern bats taken per night was 22.7 (4.2 bats/0.625 =22.7 bats; SD =15.9, SE =5.3). Based on this number, an estimated 908 northern bats exited the mine in spring (22.7 bats/night x40 nights =908 bats). This figure is atentative, minimal estimate of the hibernating population. During May and into early June 1990, few northern bats were active at Copperhead Cave. Six were taken in May, and three were taken on 2June. However, from 15 June to 5July, large numbers of males but only two females were taken (a total of 354 bats was taken in nine sessions). Our first interpretation was that the mine was serving as abachelor colony. This would have been our final interpretation, if we had sampled only once. However, if the males were quartering there, we should have had many recaptures. Only 10.7% of the captures were of banded bats (38 recaptures out of 354 total captures). Of the recaptured bats, only 2.3% (eight) were originally banded during the first sampling pe- Vol. 101 (1992) Indiana Academy of Science 133 riod. The data suggest that these northern bats were summer migrants, although we do not know where they would be going or why. The large number of northern bats that were present in this three week period precludes their being simply summer wanderers. We are unaware of other data which include extended observations on concentrations of males in summer. Fall swarming began at about the same time as it did for the little brown bat. However, the onset was more abrupt. Thirty-one males and 11females were captured on 3 1 July, after only five had been captured six days previously. Major swarming activity lasted through the first week in October. After that, the number of northern bats taken per sample remained low through December. It was not possible to tell when fall swarming stopped, because northern bats were taken throughout the winter. Pipistrellus subflavus. The numbers of pipistrelles counted while hibernating in the mine were: 201 on 23 February 1988; 113 on 14 January 1989; 99 on 27/29 December 1989; and 176 on 3March 1991. Pipistrelles apparently move about very little in their hibernaculum during winter. The water droplets that accumulate on them at that time indicate long-term hibernation in contrast to the frequent awakenings characteristic of Myotis. Most pipistrelles had left hibernation by the end of April in 1990: none were taken on 17 April; 20 were taken on 27 April; and only 3were taken on 6May. However, afew pipistrelle females were still leaving the mine through the first two weeks in May. In 1991, they left later: 16 were taken on 1May, and 9were taken on 9May. This agrees with our unpublished data indicating the formation of pipistrelle maternity colonies beginning in late April and extending through much of May. Small numbers of male pipistrelles were taken from 4 July through 31July. The mine may have served as amigratory stopover for these bats. Alternatively, these males may have represented early swarming individuals, although females were not included in swarming until the end of July. The largest number of swarming individuals was encountered on 25 August (33 males and 15 females). Swarming activity occurred throughout all of August and September and into the first week of October. At that time, the bats either moved elsewhere or entered the cave to hibernate. After 12 October 1990, no pipistrelles entered the trap until 29 March 1991. In 1989-90, however, five pipistrelles were taken on 13 October, five more were taken later in October, and 13 were taken between November and April. CONCLUSION Copperhead Cave serves as aswarming area and hibernaculum for little brown bats, northern bats, and pipistrelles. In addition, the mine may serve as amidsummer stopover for migrating northern bats and pipistrelles. LITERATURE CITED Avery, M.I. 1985. Winter activity by pipistrelle bats. J. Anim. Ecol. 54: 721-738. Brack, V. and J.W. Twente. 1985. The duration of the period of hibernation of three species of vespertilionid bats. I. Field studies. Can. J. Zool. 63: 2952-2954. Cockrum, E.L. 1956. Homing, movements, and longevity of bats. J. Mammal. 37: 48-57. Menaker, M. 1964. The frequency of spontaneous arousal from hibernation in bats. Nature 203: 540-541. Mumford, R.E. 1958. Population turnover in wintering bats in Indiana. J. Mammal. 39: 253-261. Whitaker, J.O., Jr. and L.J. Rissler. 1992. Winter activity of bats at amine entrance in Vermillion County. Indiana. Amer. Midi. Natur. 127: 52-59.