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Roost Environments for Bats

Using Abandoned Mines

in Southwestern Montana:

A Preliminary Assessment



Prepared for:



U.S. Bureau of Land Management
Dillon Field Office

Agreement Number 1422E930A960015

Prepared by:
Paul Hendricks and David Kampwerth



March 2001




MONTANA



Natural Heritage
Program



Roost Environments for Bats

Using Abandoned Mines

in Southwestern Montana:

A Preliminary Assessment



© 2001 Montana Natural Heritage Program

State Library Building • P.O. Box 201 800 • 1 5 1 5 East Sixth Avenue • Helena, MT 59620-1 800 • 406-444-3009



This document should be cited as follows:

Hendricks, P., and D. Kampwerth. 200 1 . Roost environments for bats using abandoned mines
in southwestern Montana: a preliminary assessment. Report to the U.S. Bureau of Land
Management. Montana Natural Heritage Program, Helena. 19 pp.



Executive Summary



Roost environments often abandoned mine
workings known to be used by bats were studied
in detail during 1 998-1 999 to expand on scant
knowledge of underground roost requirements for
bats in Montana. Objectives were to: ^docu-
ment daily mine ambient temperature and relative
humidity during winter and summer using elec-
tronic dataloggers, especially at underground
microsites where evidence of bat use was found,
2) document the seasons when mines were used
for roosting, and identify the bat species using the
mines, and 3) determine mine characteristics
obtained from external surveys that might be useful
for identifying underground environments suitable
for bat roosts in abandoned mines. Special
attention was paid to Townsend's Big-eared Bat
(Corynorhinus townsendii), a Montana animal
species of special concern, a Montana BLM
Special Status species, and a species of high
conservation concern throughout its range.

Four bat species were identified using these mines.
Townsend's Big-eared Bat (Corynorhinus
townsendii) was present at six mines, Western
Small-footed Myotis {Myotis ciliolabrum) at five
mines, Western Long-eared Myotis (M evotis) at
one mine, and Big Brown Bat (Eptesicusfuscus)
at one mine.

Summer ambient mine temperature was generally
too cold (usually < 1 °C) to be suitable for
maternity roosts. However, suitable sites were
present in some underground workings, and one
C. townsendii maternity roost averaged 1 1 .9 °C
during June and July. Maximum mean daily
temperature recorded in any mine was 1 4.6 °C.

Ambient mine temperature decreased significantly
as elevation increased, and summer and winter
mine temperatures were highly con-elated and
relatively predictable using time-series data.



However, complex mines at higher elevations may
contain internal microsites, not detectable from
external surveys, with temperature and relative
humidity regimes suitable at all seasons for roost-
ing bats.

Relative humidity fluctuated dramatically in many
mines, and tended to be lowest and least stable in
winter, when means in some mines were < 50%.
At two known Townsend's Big-eared Bat hiber-
nation roosts, winter mean relative humidity was
74.0% and 83 .4%, while respective ambient mine
temperatures averaged 7.5 °C and 4.4 °C.

Mine suitability for roosting bats was not apparent
from external variables, such as portal size,
number of portals, detectable airflow, or even
elevation. The most useful information obtained
during external visual inspections was the presence
or absence of obstructions at portals and the
extent of underground workings, if visible from the
portal.

All mines should first be evaluated for use by bats
before reclamation takes place. Useful informa-
tion about the potential for roost use can be
gathered from external inspections and monitoring
(visual, auditory, trapping) at mine portals. How-
ever, where possible and safe, the best method for
assessing mine structure and use by bats is under-
ground survey. Identifying mines suitable for
hibernating bats requires underground inspection.
Trapping at mine portals for pregnant and lactating
females may be effective in identifying mines used
as maternity roosts, but even here internal inven-
tory is the best survey method. Mines that are
used for night and day roosts can be effectively
monitored on multiple visits without mine entry,
preferably during different seasons, but even a
single underground visit can reveal if there is any
evidence of more extensive use by bats.



Acknowledgements



This project was funded through a Challenge
Cost-Share agreement between the Bureau of
Land Management Dillon Field Office and the
Montana Natural Heritage Program, Montana
State Library. Additional support was provided
by the Montana Department of Environmental
Quality Mine Waste Cleanup Bureau and the
USGS-Biological Resources Division,
Midcontinent Ecological Science Center.

We were aided in the field by Sam Martinez, Tom
O'Shea, Michelle Brown, and Janelle Corn. Tom



O'Shea (USGS-BRD) kindly provided on loan
some of the data loggers used during this study.
We also thank Lee Flath (Lewis and Clark Cav-
erns State Park) for granting access to the Gyp-
sum adits, and Marian and Max Johnson (Ravalli)
for permission to visit the McDonald Mine adits.
Cedron Jones (MTNHP) produced the map.

The report was reviewed and edited by John
Carlson (MTNHP) and Joy Lewis (MTNHP),
and produced with the help of Katrina
Scheuerman(NRIS).



11



Table of Contents



INTRODUCTION 1

METHODS 1

RESULTS ....2

Mine habitat features 2

Mine temperature and relative humidity. 2

Bat use of mines 8

DISCUSSION AND RECOMMENDATIONS 9

Roost environments 9

Management implications 11

LITERATURE CITED 12

APPENDIX 1 . Continuous temperature and relative humidity profiles for nine mines 15

FIGURES AND TABLES

Figure 1 . Map of mine sites 3

Figure 2. Mean temperature decreases with increased elevation in winter 6

Figure 3. Winter/summer ambient mine temperature 7

Table 1 . Summary of physical and climatological characteristics of abandoned mines 4

Table 2. Daily mine temperature and relative humidity- winter/summer. 5

Table 3. Bats observed at abandoned mines 8

Table 4. Summary of microclimate data for Townsend's Big-eared Bat (C. townsendii) 10



ill



INTRODUCTION

Because bats spend much of their lives in roosts
(Kunz 1 982), knowledge of their roosting require-
ments provides important life-history information
for understanding habitat use and seasonal pres-
ence of most species. Furthermore, suitable
summer and winter roosts may limit local and
regional distribution and relative abundance of
many temperate-zone bats (Humphrey 1 975,
Dobkin et al. 1 995), especially cave-dwelling
taxa. Thus conservation and protection of roosts
are critical long-term management activities for the
perpetuation of many North American bat species
(Sheffield etal. 1992).

Bat populations in many natural caves have
declined or disappeared because of a variety of
human-induced disturbances (LaVal and LaVal
1 980, Richter et al. 1 993, Turtle and Taylor
1 994). Abandoned and undisturbed mines now
serve as principle summer and winter roosts for
many cave-dwelling species (Turtle and Taylor
1 994) because mines offer a variety of subterra-
nean microclimates similar to those present in
natural caves (Turtle and Stevenson 1 978).
Concern about the status of North American bat
populations increased dramatically in recent
decades (Pierson 1 998) when it was recognized
that significant numbers of abandoned mines were
being barricaded, backfilled, and blasted shut for
safety and liability reasons, without prior biological
survey to determine their significance for roosting
bats.

We conducted a survey of abandoned mines on
BLM lands in southwestern Montana during the
summers of 1 997 and 1 998 (Hendricks et al.
1 999) to assess and characterize their use by bats
prior to potential reclamation activity. We antici-
pated that our work would help managers identify
sites currently used by bats, and that the informa-
tion characterizing used abandoned mines might
guide future mine survey and reclamation activity.
We gathered long-term climate data from used
abandoned mines because roost climate is a major
influence on roost site use. Roost environment



descriptions (especially temperature and relative
humidity at roost microsites) are very limited for
bats in Montana, and most available data pertain
to roosts in caves (Worthington 1 99 1 , Madson
and Hanson 1992, Hendricks 2000, Hendricks et
al. 2000).

For each mine inspected internally in 1 998 and
considered safe for reentry we placed electronic
data loggers to record daily mine temperature and
relative humidity over a 6- 1 2 month period. Our
objectives for this phase of the study were to: 1 )
document daily mine ambient temperature and
relative humidity during winter and summer,
especially at underground microsites where we
found evidence of bat use, 2) determine the
seasons when mines were used for roosting, and
identify the bat species using the mines, and 3)
determine mine characteristics documented from
external surveys that might be useful for identifying
underground environments that are suitable for bat
roosts in abandoned mines. Of special interest
were mines used by Townsend's Big-eared Bat
(Corynorhinus townsendii) because this bat is a
Montana animal species of special concern, a
Montana BLM Special Status species, and a
species of high conservation concern throughout
its range (Pierson et al. 1 99 1 , Pierson et al. 1 999,
Sherwin etal. 2000).



METHODS

We concentrated our study on ten mines between
45°10 , Nand47°16 , N latitudes in southwestern
Montana (Figure 1), six mines in Beaverhead,
Madison, and Silver Bow counties, supplemented
with four mines in Jefferson and Lake counties
known or suspected to be used by Townsend's
Big-eared Bat. Elevation of mines ranged from
853 m to 2249 m (Table 1). Mines used by bats
were identified first from historical records or by
external inspection during summer, and through
use of electronic bat detectors (ANAB AT II,
Titley Electronics, Ballina, Australia) and mist-net
or harp trap sampling at portals.



We surveyed each mine internally at least twice to
the fullest extent possible where deemed safe. No
vertical workings (shafts) were entered during this
study. At least two people entered each mine
during surveys. We recorded presence, number,
location, and identity of bat species when possible.
During surveys, we recorded the following "struc-
tural" habitat variables: vegetation cover at the
mine, portal elevation, number and size of portals,
length of underground workings, presence of
standing water, cross-section dimensions of main
tunnels, and number of levels. We ranked mine
complexity as simple (main passage with non-
branching side tunnels), moderate (main passage
with branching side tunnels or < 3 levels), or
complex (main passage with multiple branching
side tunnels or > 2 levels).

We gathered time-series temperature and relative
humidity data by installing at least one data logger
(HOBO H8, Onset Computer Corporation,
Pocasset, Massachusetts) in each mine, usually
near microsites where bats or bat sign were
observed. In two shallow mines data loggers
were placed where we considered the mine
environment likely to be the most stable. Fifteen
data loggers were placed in the mines; only two
mines contained more than one data logger. Data
loggers were attached to an extendable aluminum
rod and positioned < 30 cm below the tunnel
ceiling. Data loggers were set to record tempera-
ture and relative humidity every six hours. We
calculated daily means from these data and used
daily mean values in the analyses we present in this
report.

Because of the small sample of mines studied our
analyses are largely inferential. Where statistical
analyses were performed we followed standard
procedures (Sokal and Rohlf 1981) using Statistix
version 2.0 (Analytical Software, Tallahassee,
Florida).



RESULTS

Mine habitat features. Use by bats of aban-
doned mines in our sample did not appear related



in any obvious way to vegetation cover, mine size
or complexity (Table 1 ), size or number of portals,
or availability of standing water. All mines were in
sagebrush or sagebrush intermixed with scattered
conifers, and all mines had either one or two
functional portals with dimensions that ranged from
1 .2-2. 1 m high by 1 .2-2.0 m wide. Five of the
mines contained standing water. Six mines
(McDonald Adits #1 and #2, Gypsum Adits #1
and #2, Union, Hendricks) had some form of gate
at their portals.

Mine temperature and relative humidity. We

placed data loggers in six mines in September and
retrieved them the following August (Table 1). At
four mines we placed data loggers in December or
January and retrieved them the following July.
Data loggers failed to record for the duration of
installation at two mines; in the GypsumAdit#l
the logger failed to record any data, and in the
Unnamed Adit #3 the logger became wet and
ceased operation by March, 1 74 days after
installation. Continuous temperature and relative
humidity profiles are shown in Appendix 1 for all
loggers that recorded any data.

Maximum daily temperature recorded among the
mines (Table 1) was 14.6 °C in late July at the
Unnamed Adit #2. However, portions of some
mines never achieved temperatures > 6 °C, even
in summer (Appendix 1 ). The lowest mine tem-
perature, -1 5.9 °C, was recorded in late Decem-
ber; in general mine temperatures dropped below
freezing only in mines or portions of mines where
there was significant movement of air. In several
mines, relative humidity reached lowest values
near or below 30% during December or January
while maximum values (85-1 00%) were recorded
in July or September (Appendix 1 ).

Table 2 shows mean temperature and relative
humidity data from each mine for the same winter
and summer time periods, thereby making com-
parisons among mines the most meaningful. Mean
temperatures for January through April varied from
-1 .4 °C to 1 1 .8 °C, depending on the mine and
location within the mine. Interestingly, the ex-
tremes were found in the same mine, the




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Figure 1 . Location of abandoned mines in southwestern Montana where
mine climates were studied during 1 998-1 999.



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Hendricks. Hie June to mid-July extremes in
mean temperature (3.6 °C and 12.2 °C) also
occurred in the Hendricks Mine. Extreme values
occurred in this mine because of significant air
movement through parts of the workings, while
other parts experienced very little air movement.
For all data logger locations, summer mean
temperatures were 2.5 ± 2. 1 °C warmer than in
winter. The same pattern was evident for relative
humidity; summer means were 1 2. 1 ± 9.2%
greater than in winter. However, in the Main Drift
of the Hendricks Mine summer relative humidity
was actually a few percent lower than in winter
(Table 2), the only data logger location where this
occurred.

Mean mine temperature tended to decrease with
increased elevation in both winter and summer
(Figure 2), but relative humidity did not show a
significant elevation trend for either period (winter:
r = -0.364, P = 0.376; summer: r = -0.308, P =
0.458). For both temperature and relative humid-
ity, summer means were highly and positively



correlated with winter means (Figure 3). How-
ever, variation (measured as the standard devia-
tion) in temperature and relative humidity for the
winter and summer periods at each data logger
location was only weakly correlated (r = 0.3 87, P
= 0.191 and r = 0.165, P = 0.591).

We noted significant airflow in three mines, the
Union, Hendricks, and Unnamed Adit # 2, and
slight airflow in the shallow location of the
McDonaldAdit#l. In the Union and Hendricks
mines, we never saw bats or concentrations of
droppings where airflow was greatest (the first
level of the Union, Graeter Tunnel and First Drift in
the Hendricks), although scattered droppings were
present in these portions of the mines (Table 2).
Mean temperature difference between winter and
summer was larger at locations where there was
significant air movement (4.88 ± 1 .26 °C versus
1.03 ± 0.70 °C: f = 7.19, df = 11, P < 0.001).
Air movement did not have a similar effect on the
mean difference in winter and summer relative
humidity (t = 0.79, P = 0.444).



Table 2. Daily mine temperature (°C) and relative humidity (%) for winter (10 Jan-30
Apr) and summer (1 Jun-13 Jul). Values are means ± 1 standard deviation. Asterisk
indicates location is a known bat hibernation site (winter) or a maternity/day roost site
(summer).



Mine


Winter (n


= 111 days)


Summer (n


= 43 days)




Temp


Ivfcl


Temp


RH


McDonald Adit #1 (shallow)


7.5 ±0.9*


74.0 ± 9.4


10.5 ± 0.4*


97.4 ±2.7


(deep)


10.0 ±0.4


98.2 ±1.4


11.3 ±0.2*


100.0 ±0.4


McDonald Adit #2


10.7 ±0.2


89.0 ±2.0


11.9±0.5*


91.7 ±4.7


Gypsum Adit #2


4.4 ±0.9*


83.4 ±4.2


6.7 ±0.2


97.8 ± 0.6


Gypsum Adit #1












Unnamed Adit #2


2.8 ± 1.7


56.1 ±6.9


9.2 ±1.5


63.0 ± 13.0


Unnamed Adit #3





_-_






Unnamed Adit #1


7.2 ±0.4


49.9 ±3.4


8.7 ±0.5


69.2 ±12.6


Union


2.8 ± 1.1


59.2 ±7.6


7.9 ±1.5


74.4 ±14.7


Hendricks First Drift


-0.9 ±1.4


71.7±9.6


3.6 ±0.3


84.5 ±2.1


Graeter Tunnel


-1.4 ±2.7


69.8 ±9.9


3.9 ±0.3


86.2 ±1.7


Main Drift


9.1 ±0.2*


77.5 ±2.0


9.7 ±0.2


74.7 ± 0.4


Solution Cavity


11.8±0.1


42.6 ± 6.2


12.2 ±0.0*


65.2 ±2.0


West Drift


10.6 ±0.0


44.0 ±6.8


10.7±0.1*


67.3 ±1.9


Ruth & Copper Bottom


4.1 ±0.4

— i


98.7 ±2.0

, I


4.9 ±0.2


100.0 ±0.0



Q.
<

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(0

—)

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<u

3

(0
w


Q.

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m

<x>

c




600 800 1000 1200 1400 1600 1800 2000 2200 2400

Mine elevation (m)



c

3



O

g)

3

S

Q.

E
m

c




600 800 1000 1200 1400 1600 1800

Mine elevation (m)



2000 2200 2400



Figure 2. Mean mine temperature decreases with increased elevation in winter (Jan- Apr: r -
-0.744, P = 0.034) and summer (Jun-Jul: r = -0.828, P = 0.01 1) in southwestern Montana. Points are
mean values for individual mines, using data from Table 2. Dashed line is the 95% confidence interval.



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2 4 6 8 10

Mine temperature (C): Jan-Apr



12



14



100



c

3






3

x:
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= 60 -




60 70 80 90

Mine relative humidity (%): Jan-Apr



100



Figure 3. Winter (Jan-Apr) and summer (Jun-Jul) mine ambient temperature (top: Y= 0.608X + 4.874, R 2
= 0.823) and relative humidity (bottom: Y = 0.657X + 36.201 , R 2 = 0.792) are highly correlated (P <
0.00 1 ) in southwestern Montana. Points represent individual datalogger locations, using the data from Table
2. Dashed line is the 95% confidence interval.



7



Bat use of mines. We observed four species of
bats at the ten mines (Table 3). Corynorhinus
townsendii was present at six mines, Myotis
ciliolabrum at five mines, and M. evotis and
Eptesicusfuscus at one mine each. In all cases,
we observed only small numbers of individuals.

Three of the mines (McDonald Adit #1 , Gypsum
Adits #1 and #2) were hibernacula for C.
townsendii, with number of hibernating individuals
ranging from 1-8. A11C. townsendii in the
McDonald Adit #1 were roosting singly on the
walls < 1 .0 m above the floor within 40 m of the
portal. In the Gypsum Adit #1 a single C.
townsendii was on the wall <1 .0 m above the
floor and 13.8m from the portal. In the Gypsum
Adit #2 we found torpid bats (1 unidentified
Myotis and 7 C. townsendii) between 6.0-25.5
m from the portal; all bats were <1 .0 m above the
floor and roosting singly. In the only other mine
entered during winter (Hendricks) we found single
M. ciliolabrum and E. fuscus, both about 1.5 m
above the floor 143 m from the portal. A mater-
nity roost of 25 C. townsendii in the McDonald
Adit #2 was the largest number of bats we found



in a single mine; these were in a tight cluster on the
wall near the ceiling about 1.5 m above the floor
and 14 m from the portal. We found no other
maternity roosts.

The remaining bats we observed or captured
(Table 3) appeared to be using the mines as day
or night roosts. The single M. ciliolabrum we
found in June in the Hendricks Mine was a female
fully exposed on the wall near the ceiling about 1 .5
m above the ground. Three of five M.


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