Our l.nhifi Resources — Mammals 



97 



The Indiana bat {Myotis sodalis) is an endan- 

 gered species that occurs throughout much 

 of the eastern United States (Fig. I ). Although 

 bats are sometimes viewed with disdain, they 

 are of considerable ecological and economic 

 importance. Bats consume a diet consisting 

 largely of nocturnal insects and thereby are a 

 natural control for both agricultural pests and 

 insects that are annoying to humans. 

 Furthermore, many forms of cave life depend 

 upon nutrients brought into caves by bats in the 

 form of guano or feces (Missouri Department of 

 Conservation 1991). 



• Priority 1 liibernacuia ' 

 D Range of bat 



Fig. 1. Range of tlie Indiana bat and locations of Priority 

 1 liibernacuia [see text for definition.s). 



Indiana bats use distinctly different habitats 

 during summer and winter. In winter, bats con- 

 gregate in a few large caves and mines for hiber- 

 nation and have a more restricted distribution 

 than at other times of the year. Nearly 85% of 

 the known population winters in only seven 

 caves and mines in Missouri. Indiana, and 

 Kentucky, and approximately one-half of the 

 population uses only two of these hibemacula. 



In spring, females migrate north from their 

 hibemacula and form maternity colonies in pre- 

 dominantly agricultural areas of Missouri, 

 Iowa, Illinois, Indiana, and Michigan. These 

 colonies, consisting of 50 to 150 adults and 

 their young, normally roost under the loose bark 

 of dead, large-diameter trees throughout sum- 

 mer; however, living shagbark hickories (Cciiya 

 ovata) and tree cavities are also used occasion- 

 ally (Humphrey et al. 1977; Gardner etal. 1991; 

 Callahan 1993; Kurta et al. 1993). 



As a consequence of their limited distribu- 

 tion, specific summer and winter habitat 

 requirements, and tendency to congregate in 

 large numbers during winter. Indiana bats are 

 particularly vulnerable to rapid population 

 reductions resulting from habitat change, envi- 

 ronmental contaminants, and other human dis- 

 turbances (Brady et al. 1983). Additionally, 

 because females produce only one young per 



year, recovery following a population reduction 

 occurs slowly. Concerns arising froin the high 

 potential vulnerability and slow recovery rate 

 have led to a long-term population monitoring 

 effort for this species. 



Bat Census Design 



The first rangewide census of wintering 

 Indiana bats was made in 1975. All subsequent 

 population data were gathered according to 

 standardized cave census techniques established 

 by the Indiana Bat Recovery Team in 1983 

 (Brady et al. 1983). Data presented in this arti- 

 cle are based upon counts made at 2-year inter- 

 vals at Priority I hibemacula, which are caves 

 where winter populations exceeding 30,000 

 bats have been recorded. We chose to use data 

 only from Priority I caves because they contain 

 the majority of bats in the population. During 

 midwinter cave censuses, bats hanging singly 

 and in small clusters of up to 25 were counted 

 indi\ idually. The number of bats in larger clus- 

 ters was determined by multiplying the surface 

 area of the cluster by bat density (Fig. 2). 



Bat Populations: Trends and 

 Recovery Prospects 



Before the I970"s. the population status of 

 Indiana bats was poorly understood because the 

 locations of many of their winter hibemacula 

 were unknown, and the counts that were con- 

 ducted were made irregularly and inconsistent- 

 ly. The 1975 census established a benchmark of 

 nearly 450.000 bats using Piiority 1 hibemacu- 

 la. Since 1983 the number of bats tallied has 

 declined significantly, reaching a low of 

 347,890 during the most recent census in 1993 

 (Fig. 3). 



Indiana Bats 



by 



Ronald D. Drobney 



National Biological Service 



Richard L. Clawsoii 



Missouri Department of 



Conser\'ation 



Fig. 2. Hibernating cluster of Indiana bats 



