The Role of Small Caves as Bat Hibernacula in Iowa

Abstract

Small caves provide habitat for a variety of species, including bats. Past research on cave bats in Iowa has focused on a few large caves. Large caves are uncommon and represent only a portion of the known caves in the state. Since few hibernacula are protected in Iowa and no assessment of small caves has been done, bat census data were compared to cave morphology to determine the significance of small caves as hibernacula. Twelve years of census data (1998–2009) were reviewed for small caves (# 50.0 m in length) where hibernating bats had been documented. Four morphological features were compared against the data: entrance aspect, entrance size, cave length, and internal surface area. Student’s t-test and Spearman rank correlation were used to test for relationships between the presence and abundance of each species and each of the four morphological features. The eastern pipistrelle occurred in 68% of the caves, and the little brown bat in 24%. Student’s t-test showed a significant correlation with cave length for eastern pipistrelles. Spearman rank correlation showed a significant negative correlation with entrance aspect and significant positive correlations for cave length and internal surface area for eastern pipistrelles. The results are different from previous studies on larger Iowa caves, which showed big brown bats and little brown bats as the most abundant species. Eastern pipistrelles preferred larger caves with vertical entrances. However, large is a subjective term, and the results indicate that small caves are an important source of hibernacula for the eastern pipistrelle.