Abandoned Mines as Bat Habitat
by J. Scott Altenbach
This article was originally published in the US National
Park Service CULTURAL RESOURCE MANAGEMENT
magazine - No 7 -;1998
Over the last decade, an increasing concern about liability
by private and public land owners, as well as federal and state agencies, has
prompted an exponential increase in the efforts to safeguard abandoned mines.
Abandoned mines have long been recognized as habitat for a large number of bat
species as well as other kinds of wildlife. Since safeguarding typically involves
destruction by blasting or backfilling, this has stimulated growing interest in
their potential for wildlife habitat. Although a systematic
program of evaluation of abandoned mines prior to closure has been slow to implement, enough mines have
been surveyed to illustrate that they are a significant habitat resource for bats
of several species. Of the thousands of abandoned mines in the West which have been
surveyed over the last ten years, roughly half have shown some type of use by bats
and about 10% have shown some form of significant use. The difficult question of
what constitutes significant use has been addressed by
Altenbach and Milford (1995),
Altenbach and Pierson (l995), Tuttle and Taylor (1994), and
others. Use by maternity colonies of any kind, use for large hibernating colonies,
use as a migratory stopover, and use for colonial reproductive behavior are
relatively clear examples. Prudence dictates that any kind of use that is previously
undocumented qualifies as well. Significance of use varies regionally and is
generally best determined by the best judgment of bat biologists familiar with the
region.
Large numbers of underground mines were not a common feature of the environment
in the western United States until a few decades before the dawn of the 20th century.
Why should any effort be made to protect a habitat, especially one that presents
a potential hazard to humans, that did not exist until recent times? By the same
reasoning, we should not need wildlife preserves or national parks. Many bat
species are in decline as a direct or indirect result of human activity. A
significant part of this decline can be attributed to destruction of natural roost
sites or human disturbance at roost sites. Species such as Townsend's big-eared
bat are notorious for establishing maternity colonies in relatively exposed parts
of caves and rock shelters. Equally notorious is their habit of abandoning a roost
site, and their newborn young as well, because of a relatively slight disturbance.
Recreational activities, although perhaps inadvertent, have had a strong negative
impact on a number of bat species. Roost habitat destruction because of encroaching
development, logging of old growth forests, and renewed mining have also taken a
toll. Oddly enough, the micro-habitat presented by concavities in "snag" trees is
duplicated by the micro-habitat provided in some abandoned mines.
Twenty-eight of the 45 species of bats found in the continental United States are
known to roost in underground mines. In California, the only known colonies of the
Cave myotis, all of the winter and most of the summer roosts of the California
leaf-nosed bat, and roughly one third of all Townsend's big eared bat roosts are
in abandoned mines Altenbach and Pierson (l995). All of the known
maternity colonies of the endangered Lesser long-nosed bat in the United States
are in abandoned mines (V. M. Dalton, pers. comm.), as are the majority of maternity
and hibernating colonies of Townsend's big-eared bats in New Mexico. Abandoned
mines provide a refugium in the face of loss of natural habitat. They can be
likened to "Noah's Arks" which may allow some bat species to survive in the face
of continuing disturbance at natural roost sites. Simultaneous safe-guarding and
protection of a small number of abandoned mines with bat-compatible closures or
"bat gates" promises to buy some time and allow more informed decisions to be made
about their long term survival. Hopefully, natural roost sites can be protected
although it seems quite possible that protected abandoned mines could easily be
the primary roost habitat for some of these species.
Nevada's mine closure program illustrates the potential for impact that abandoned
mine closure can have on bat populations. Before state personnel were aware of the
bat habitat potential of abandoned mines, the Nevada Abandoned Mine Lands Bureau
closed or facilitated the closure of roughly 3,000 mine features without any type
of wildlife survey. If we conservatively estimate that 5% of Nevada's abandoned
mines had significant bat use, then roughly 150 mines with significant bat use,
and probably in some cases with the bats in them, were destroyed by backfilling.
Even though abandoned mines are a patchy feature of the environment, hundreds of
thousands of them are scattered over the western states. When the impact of the
Nevada mine closure program is extrapolated regionally, the potential for extreme
negative impact to bat populations is easily seen.
Evaluation of the Resource
Bat surveys in anticipation of abandoned mine closures vary from thorough to
non-existent. They depend upon whether the entities doing the closure are public
or private, whether the personnel involved have even heard that mines are used by
bats and that bats may be worthy creatures to protect, whether money is available
to do surveys and construct bat-compatible closures, as well as the general
vagaries of human nature. Although mine closure programs using federal monies are
mandated by National Environmental Policy Act regulations to evaluate mine features
for wildlife habitat, those using state or private dollars generally are not.
For example, a state-based Abandoned Mine Lands Program funded by the mining
industry is not subject to federal guidelines. At a 1994 public meeting,
representatives from a mining company stated with some pride and enthusiasm that
they would backfill every abandoned mine on their property without considering
possible wildlife use and there was nothing anyone could do about it. In contrast,
other mining companies have gone out of their way trying to do the right thing.
A program to evaluate abandoned mines for significant bat use first requires the
education of the private and governmental entities involved with mine closure.
The bat habitat-abandoned mine workshops organized by Bat Conservation International,
in partnership with corporate, state and federal agencies, have informed numerous
individuals and companies about the problem and some of the solutions to it. Some
of the best success stories, i.e., mines with significant
bat populations safeguarded with bat-compatible closures, have occurred because
informed people were aware of the importance of the issue and took appropriate
actions. Since there are not unlimited funds to protect abandoned mines as bat
resources, protection first requires careful evaluation of the resource.
Although bat biologists continue to learn more about the diverse factors which
make abandoned mines suitable for bat habitat, we have not yet reached a level
of understanding that allows evaluation of specific bat use, or even the potential
for use, without a careful examination of the actual mine in question.
Bat surveys of abandoned mines can be internal (underground), external, or a
combination of both. External surveys are time consuming, labor intensive, require
specialized equipment and training, and require considerable knowledge of
abandoned mines and especially the bats that use them. Although this approach can
detect warm season use, it is useless for detecting hibernation, especially if
small numbers of bats are present. If a mine cannot be fully evaluated because
portions of its workings are inaccessible, or because entry presents unacceptable
risks, an external evaluation is the only option. In practice, a combination of
underground and external evaluation is generally necessary.
Internal surveys are the least labor intensive and most effective means to survey
abandoned mines for bat use. However, this procedure requires personnel who are
underground-trained and experienced, properly equipped, and experienced in bat
biology. Unfortunately, there are many individuals attempting to do internal
abandoned mine surveys who fail to meet the qualifications for underground survey
and who pose safety risks to themselves and others.
It is essential, therefore, to continue efforts to increase awareness about both
the potential shortcomings of current mine evaluations and the actual complexity
of historic mining operations. Training for external evaluation has been part of
the ongoing bat habitat-abandoned mine workshops, but that training is very
generalized. Underground training has been nonexistent, partially because of
liability-related concerns on the part of those who would do the training.
Although Mine Safety and Health Administration training and certification is a
prerequisite for anyone doing underground surveys, it is primarily intended for
individuals working in active mines. As such, the program does not include
information concerning some of the most common hazards associated with inactive
mines, e.g., the kinds of pertinent gas detection apparatus and their limitations,
or how to recognize old explosives. Implementing comprehensive training programs
would ensure competent researchers who were able to effectively evaluate bat use
in abandoned mines. Correcting these education-related deficiencies would go a
long way to ensuring that historic mines would be properly evaluated prior to
proposed closure programs.
Bat-Compatible Closures
If survey data reveal that a mine is used by bats and if the use is significant,
the mine would be an ideal candidate for protection with a bat-compatible closure
that precludes public access, but allows bats to use the site. However, the decision
to install a bat-compatible closure depends upon a variety of other factors.
Appropriate questions to consider include: Are alternative features, used in the
same way, nearby? How feasible is a bat-compatible closure for a particular mine
entry? Will preservation of an abandoned roost provide habitat or mitigate habitat
destruction elsewhere?
The bat-compatible closures used by the New Mexico Abandoned Mined Lands Program
are designed by staff engineers and are similar to the designs preferred by the
American Cave Conservation Association. Current designs, generally constructed
with crossbars of heavy angle iron reinforced with stiffeners, are difficult for
vandals to breach. Tuttle and Taylor (1994)
and Dalton and Dalton (1995) summarize
design details; the American Cave Conservation Association is a further source for
gate designs. Of the many hundreds of bat-compatible gates installed in the United
States, relatively few have been breached by vandals. In New Mexico, the percentage
of breached gates is lower than the percentage of failures for non-bat-compatible
closures. All types of mine closures must be monitored for possible failure. A mine
cannot be closed and then forgotten.
Timing of Mine Closure
The selection of an appropriate "time window" for permanent sealing or safely
installing a non-bat-compatible closure must minimize the possibility that known
or unknown resident bat species will be trapped inside. Installation of
bat-compatible closures must likewise be timed to minimize disturbance of residents.
Timing will vary with the type of use, the species present, and the region. Closure
activities need to be explicitly coordinated with local bat biologists.
Conclusion
We know that abandoned mines are important habitat, in some cases vital habitat,
for a large number of bat species. We know how to survey mines for bat use and
we have a good idea what constitutes significant use. We have considerable
experience with designing bat-compatible closures, we know how bats deal with
them, and we know their installation can result in increased bat use within
protected mines. We know that bat-compatible closures can be defeated by vandals,
but this becomes less likely as designs improve. We know that bat-compatible
closures have to be monitored just like any other mine closure. If we can continue
to learn and apply what we know, several bat species, currently in serious jeopardy,
will have an improved chance of survival well into the next century.
Anyone wanting to learn more about the bat
habitat-mines program should contact the
Bats and Abandoned Mine
Project, Bat Conservation International, P.O. Box 162603, Austin, Texas 78716,
(telephone 512-327-9721).
Scott Altenbach is a Professor of Biology at the University
of New Mexico. Since 1991, he has undertaken bat surveys of abandoned mines for
the New Mexico Abandoned Mined Lands Program as well as for public and private
concerns, including the National Park Service, in other states. He worked briefly
as a miner in his undergraduate days, has logged over 6,000 underground hours,
and has examined over 1,800 abandoned mines.
References
Altenbach, J.S. and H. E. Milford, 1995 Evaluation and
management of bats in abandoned Mines in New Mexico. In: D. Pate, ed.
Proceedings of the 1993 Cave Management Symposium, Carlsbad, New Mexico, pp. 326-330.
Return to Introductory Material
Altenbach, J.S. and E.D. Pierson, 1995 The importance of mines
to bats: an overview. In: Riddle, B.R., ed. Inactive mines as bat habitat:
guidelines of research, survey, monitoring and mine management in Nevada.
Biological Resources Research Center, University of Nevada, Reno.
Altenbach, J.S., 1995 Entering mines to survey bats effectively
and safely. In: Riddle, B.R., ed. Inactive mines as bat habitat: guidelines
of research, survey, monitoring and mine management in Nevada. Biological Resources
Research Center, University of Nevada, Reno.
Dalton, V.M. and D.C. Dalton, 1995, Mine closure methods
including a recommended gate design. In: Riddle, B.R., ed., Inactive mines
as bat habitat: guidelines of research, survey, monitoring and mine management in Nevada.
Biological Resources Research Center, University of Nevada, Reno.
Return to Bat-Compatible Closures
Tuttle, M.D. and D.A.R. Taylor, 1994 Bats and Mines.
Bat Conservation International, Austin, TX.
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