378 Northeastern Naturalist Vol. 18, No. 3 Surge Tunnels in Quarries as Potential Hibernacula for Bats Robin M. Slider1 and Allen Kurta2,* Abstract - We document use of surge tunnels at an abandoned quarry as hibernacula for bats and suggest that other such tunnels may be easily modified to create new hibernacula. Surge tunnels in Alpena County, MI, made possible a 230-km range extension for Perimyotis subflavus (Eastern Pipistrelle). Most insectivorous bats that summer in northern latitudes hibernate in winter, subsisting on stored fat until spring, when their prey once again becomes active. Naturally occurring hibernacula in the North are usually caves or deep rock crevices, although bats have adopted many types of artificial cavelike environments for hibernation, especially mines (Neubaum et al. 2006, Ransome 1990, Tuttle and Taylor 1998). Presence or absence of suitable hibernacula, whether natural or artificial, can influence species richness and the relative abundance of species in the local assemblage of bats (Humphrey 1975). In this paper, we describe a previously unreported type of human-made hibernaculum, show that this hibernaculum has made possible a 230-km range extension for Perimyotis subflavus (Kerr) (Eastern Pipistrelle), and suggest possible uses of such hibernacula in the fight against white-nose syndrome, an emerging disease that has killed over 1 million bats in the Northeast (Blehart et al. 2009, Frick et al. 2010). The newly identified hibernaculum is called a “surge tunnel” or “reclaim tunnel”. These tunnels typically are made of concrete and constructed near rock-crushing machinery in a quarry. The product of the crusher is heaped into a “surge pile” on top of the tunnel, often to heights of 10–20 m or more. Trap doors in the ceiling of the tunnel can be opened as needed so that the rock spills through chutes onto a conveyor belt, which then transports the material elsewhere in the quarry for further processing or shipping. On 14 March 2010, we visited an abandoned limestone quarry about 16 km northeast of Alpena, Alpena County, in the northern Lower Peninsula of Michigan, and searched two surge tunnels for hibernating bats. The northern tunnel was about 150-m long and made of 0.5-m-thick concrete. About 120 m of the tunnel was still covered by old surge piles of gravel-sized stones (Fig. 1). The interior of the arched passageway was 3-m wide at the base and 3.7-m high at the center. Along the tunnel on either side, there was a series of 1.2-m-wide chutes that had been used to channel the gravel onto conveyors, but all were closed and rusted shut at the time of the survey, except one that provided access for us and presumably the bats. Dripping water from melting snow above the tunnel occurred at various points, and standing water began about 50 m from the entrance and continued to the end, where the water was 1.4-m deep. Using a sling psychrometer, we determined that air temperature at the terminus was 3.3 °C, with relative humidity at 95%. The inner walls of the tunnel were typically smooth concrete (Fig. 1), and most bats were either roosting on rougher concrete where the bottom of the chutes intersected the wall (2.7 m above the ground) or in openings created for recessed lighting fixtures along the midline of the ceiling. We counted 64 bats, including 57 individuals of Myotis, 5 of Eptesicus fuscus Palisot de Beauvois (Big Brown Bat), and 2 of P. subflavus. Although we did not examine the Myotis in hand because of the height at which they roosted, all 1Department of Teacher Education, Eastern Michigan University, Ypsilanti, MI 48197. 2Department of Biology, Eastern Michigan University, Ypsilanti, MI 48197. *Corresponding author - akurta@ emich.edu. Notes of the Northeastern Nat u ral ist, Issue 18/3, 2011 378 2011 Northeastern Naturalist Notes 379 Figure 1. Top: external view of the top of the northern tunnel, as it disappeared under remnants of the surge pile. Bottom: interior view of the northern tunnel. 380 Northeastern Naturalist Vol. 18, No. 3 appeared to be Myotis lucifugus Le Conte (Little Brown Bat). One P. subflavus was preserved as a specimen in the Michigan State University Museum (#37630). The southern tunnel was only about 70 m long. Chutes were unpaired and centered on the ceiling. Most of the tunnel was uncovered along the top, and in general, depth of material covering the southern tunnel was less than that over the northern tunnel. Also, instead of gravel, stones associated with the southern tunnel were larger, about 15–25 cm across. These stones had been dumped into each chute, all of which were still open, and as the stones fell, they spread in a cone-shaped pattern, filling most of the tunnel. However, along either side of the cone, adjacent to the chute, there was open passage, barely large enough for a human. Although we did not bring the psychrometer on the arduous crawl into the tunnel, the environment generally was not suitable for hibernation—light penetrated through the open chutes at multiple locations, airflow was noticeable, and frost often occurred on the walls. Despite these conditions, a third P. subflavus, the only bat present, was found in the second tunnel. Limestone caves do not occur in the Lower Peninsula of Michigan, which is covered by glacial till, and there are no open mines that can be used by bats in winter (Davies 1955, Dorr and Eschmann 1970). The lack of hibernacula in this large geographic area and the short migratory distances traveled by P. subflavus (Griffin 1940) meant that these bats historically did not occur in the region (Brack and Mumford 1984; Kurta 1982, 1995). Nevertheless, P. subflavus has invaded Lower Michigan, most likely through northwestern Indiana, within the last 35 years (Kurta et al. 2007). All previous observations of this species in northern Indiana and Lower Michigan were associated with the coast of Lake Michigan, and most were associated with two artificial hibernacula—Bear Cave, a tufa cave greatly enlarged and modified by humans, near Buchanan, Berrien County, MI, and Tippy Dam, a hydroelectric facility with a hollow spillway, near Wellston, Manistee County, MI. The quarry near Alpena, however, is along the coast of Lake Huron, about 230 km northeast of the closest previous records of P. subflavus, which occurred at Tippy Dam (Kurta et al. 2007). P. subflavus provides an example of a mammalian species that has benefited greatly from human activities, which have allowed this bat to extend its range across much of the Upper Midwest by colonizing one artificial hibernaculum after another (Brack and Mumford 1984; Kurta 1982, 1995). Surge tunnels are commonly found at large quarries, and we suggest that these sites are used by hibernating bats throughout the North. Even if a particular surge tunnel is not occupied by bats because of unsuitable temperature and humidity, we propose that these environmental problems could easily be remedied. Surge tunnels are built to withstand tens of meters of overburden, and abandoned quarries frequently have loose material available on site that could be piled on top of the tunnel to create an appropriate internal environment with minimal expenditure of time and money. Air temperature within the tunnel near Alpena, for example, likely could be increased by moving the largest remnants of the surge pile directly on top of the tunnel (Fig. 1). Furthermore, the US Fish and Wildlife Service is considering, as one of many potential strategies, creation of artificial hibernacula in which captive bats could be maintained to help temporarily buffer the detrimental effects of white-nose syndrome (L. Pruitt, US Fish and Wildlife Service, Bloomington Field Office, pers. comm.). Modification of existing surge tunnels may be more cost-effective than creating hibernacula de novo. 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