Tuesday, January 01, 2008

Gray bats


Every January since the mid-1990s, a handful of cavers don sturdy Neoprene waders and descend into a losing stream cave in Camden County to examine bat guano. Because of the thriving gray bat population that calls this cave home spring through fall, winter is the only time of year when entry to this cave is permitted.

Gray bats (unlike Missouri's other 7 bat species) live in caves year round. Between March and November, the cave in Camden County serves as a maternity roost for almost 20,000 of them. Every December, they leave the cave to return each winter to a hibernaculum site, one of eight pit caves in the Missouri and Arkansas Ozarks. After the bats leave the maternity cave, cavers hike through chest high 40 degree water to the roost site. Using a formula derived from estimating the amount of guano produced by a single bat in the course of 9 months, gray bat populations are deternmined based on the size of their guano heaps. Since 1984, the year a gate was first placed on this cave to deter people from entering, the population has increased from 200 animals to an astonishing 19,500.

Gray bats were added to the Endangered Species list decades ago. Their decline was directly linked to several factors, including pesticide use and destruction of riparian habitat. The primary reason for their decline was the regular disturbance of hibernacula and maternity sites by humans. Unlike pipistrelles and little brown bats, gray bats roost in large clusters. During the breeding season, they locate a cave near a river or stream with a high domed ceiling which serves as an incubation chamber. If anyone enters the cave during their maternity period, the mother bats will drop or abandon their young and often leave the site altogether. Before gates were installed on almost every cave in Missouri, people built fires in them to aid in exploration. As large colonies of gray bats were disturbed by the smoke and fire, they would often be shot as a form of target practice. This apparently happened regularly.

During the winter, gray bats hibernate in even larger colonies. They don't feed during the winter; instead, they live off the fat stored before the hibernation period, usually enough fat to last six months. Disturbing gray bats as they hibernate causes them to immediately lose 20-30 days worth of stored fat. While they are the largest bat in Missouri, they only weigh a little more than a quarter. So, hibernaculum sites are visited by cavers in the spring and summer while maternity sites are entered during the winter.

Gating caves has been integral to their population recovery. Unfortunately, with the installation of certain gates, air flow and, therefore, temperatures and humidities were altered. Gray bats require 56-58 degrees in their summer sites and 42-52 degrees in their winter sites. New cave gate designs have proven somewhat effective at keeping people out while protecting the fragile environment and allowing safe nightly passage for bats.

The destruction of riparian habitat has negatively impacted populations. Gray bats feed on invertebrates, many of which depend on water for some part of their life cycle. With the removal of trees and shrubs, streambanks erode and water quality declines. Moreover, widespread pesticide use causes bioaccumulation effects in gray bats. Considering their dietary requirements, nightly feasting on insects with high levels of pesticides in them can eventually kill the bats.

The protection afforded by the Endangered Species Act has helped populations rebound in the past 10 years. Gray bat caves have been identified and gated; trespassing during gray bat roost periods carries a large fine. Unfortunately, the ESA doesn't require the reinstallation of forested corridors necessary for travel between roost sites. The ESA also doesn't mandate streambank restoration of 100 ft. wide tracts of closed canopy forest which has proven beneficial to foraging efforts. Nevertheless, their population is coming back, but it's no reason to even entertain delisting.

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