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Life Sciences
Occasional Papers

Royal Ontario Museum
July 28, 1972

No. 21

Distribution and Overwintering
of My otls leibii and Eptesicus fuscus
(Chiroptera : Vespertilionidae) in Ontario

by M. Brock Fenton1

ROYAL ONTARIO MUSEUM LIBRARIES

3 1761 05162357 7

In eastern North America, Myotis leibii
(Audubon and Bachman) (= M. subulatus,
Glass and Baker, 1968), the small-footed
myotis, and Eptesicus fuscus (Palisot de
Beauvois), the big brown bat, reach their
northern limits of distribution in Ontario and
Quebec. Both hibernate in caves and aban-
doned mines but are not common in these
hibernacula. Data accumulated between De-
cember 1965 and April 1971 on distribution,
sex ratios, selection of hibernation sites, and
variation in weight during hibernation are
presented and compared with similar data
for other species, including Myotis lucifugus,
M. sodalis, M. keenii, and Lasiurus borealis.
The locations of the following abandoned
mines visited during the study are shown in
Fig. 1 : Alona Bay ( 5 ) , Gowganda ( 6 ) , Jack-
fish (3), Schreiber (2), Wawa (4) and
Webbwood (7). Also in Fig. 1 is the loca-
tion of the Cavern Lake Cave and the sites
from which specimens of M. leibii (A) and
E. fuscus (A) were reported by Peterson
( 1966). The Renfrew mine is located in On-
tario at 45°22'N, 77°08'W, and the Bryson
mine in Quebec at 45°45'N, 76°45'W.

Materials and Methods — In winter bats were
obtained by hand from hibernation sites,
while in summer they were caught in hand
nets and mist nets as they flew through

1. Department of Biology, Carleton University,
Ottawa K1S 5B6, Canada and Research Associate,
Department of Mammalogy, Royal Ontario
Museum.

hibernacula. Upon capture, bats were iden-
tified with respect to sex, species and, where
possible, age, and banded using Number 2
Bat Bands supplied by the U.S. Fish and
Wildlife Service. Bats were weighed alive to
the nearest 0. 1 g using an Ohaus triple beam
balance with an attached cage (Ohaus Scale
Corp., Florham Park, N.J.). Temperatures
were obtained with Taylor (Taylor Instru-
ments of Canada, Toronto, Ontario) and
Sci-Bor (Science Borealis Ltd., Mississauga,
Ontario) maximum-minimum thermometers,
Bacharach Tempscribe thermographs (Bach-
arach Industrial Instrument Co., Pittsburgh,
Pa.), and a Y.S.I, telethermometer (Yellow
Springs Instrument Co., Inc., Yellow Springs,
Ohio). Student-Fisher Mests least squares
regression analyses and F tests for linearity
were applied to the weight data using an
Olivetti Programma 101 (Olivetti-Under-
wood Corp., New York, N.Y.).

Distribution — Peterson (1966) reported a
specimen of M. leibii taken in Lake Superior
Provincial Park on the east shore of Lake
Superior on 21 September 1964 (Fig. 1)
and noted that the locality was some 325
miles northwest of the previous known limit
of the range. The following data were ob-
tained during investigations of summer
"swarming" activity of bats at hibernacula
(Fenton, 1969).

At an abandoned mine near Webbwood,
five male and four female M. leibii were
caught on the nights of 3-4 and 4-5 August
1968 (Fig. 1), and at a similar site near

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Figure 1

Distribution of the known occurrences of Myotis leibii and Eptesicus fuscus in northern Ontario rela-
tive to the -18°C mean minimum January isotherm (from Chapman and Thomas, 1968). Collecting
localities for specimens of E. fuscus from Peterson (1966) are indicated by ▲. that of M. leibii (Lake
Superior Provincial Park) by A- Hibernacula known for northern Ontario are indicated by □ and
numbered according to the following code: 1, Cavern Lake cave; 2, Schreiber mine; 3, Jackfish mine:
4, Wawa mine; 5, Alona Bay mine; 6, Gowganda mine; and 7, Webbwood mine. The distribution of the
-18°C mean minimum January isotherm is shown only for Ontario.

Alona Bay, two adult males of this species
were caught on the night of 5-6 August
1968. Between 6 and 12 August, this species
was not encountered at abandoned mines
near Wawa, Jackfish, Schreiber, or Gow-
ganda (Fig. 1). One torpid M. leibii was
observed at the mine near Alona Bay on 22
November 1968, but in January 1967 none
was found at the mines near Webbwood,
Alona Bay, Wawa, Jackfish, Schreiber, or
Gowganda. (Minimum outside temperatures
at the last five localities ranged from —26°
to — 40°C; Mr. B. Yorke, personal com-
munication.) Environmental conditions in
these mines were suitable for hibernation, as
witnessed by the presence of torpid M. luci-
fugus and M. keenii throughout the winter.
As two of the nine M. leibii taken at Webb-
wood in August 1968 were young of the
year, the species must breed in that area.

Eptesicus fuscus was reported by Allin
( 1942) from Cavern Lake Cave (Fig. 1) on
22 November 1941, but I did not find bats
of this species hibernating in any of the
northern Ontario hibernacula. At Webb-
wood, two male E. fuscus were caught on

the night of 4-5 August 1968, while one
male and one female young of the year
were taken at Alona Bay mine on the night
of 5-6 August 1968. Skeletal remains (rom
43625), including the skull, of one E. fuscus
were found on the floor of the Jackfish mine
on 2 October 1967. The presence of young
of the year of E. fuscus at the Alona Bay site
suggests that the species breeds in that area.

On 23 February 1972, B. Trevor-Deutsch
and G. Muller found three torpid E. fuscus
at the Cavern Lake Cave, and a day later,
one torpid E. fuscus at the Schreiber mine.
These represent the first E. fuscus observed
from the north shore of Lake Superior in
mid-winter.

Myotis leibii and E. fuscus were found in
hibernacula near Alona Bay and Webbwood
during August, but the former species has
not been taken in other hibernacula in north-
ern Ontario in January, suggesting that M.
leibii may migrate south to overwinter. Since
E. fuscus has not been consistently recorded
from northern hibernacula in mid-winter,
some individuals of this species might also
migrate south for the winter. Such an ex-

planation would account for the absence of
females and young of M. leibii at Alona Bay,
as pregnant females might be able to fly only
limited distances from hibernacula to sum-
mer roosts that are suitable for parturition
and rearing of young. Eptesicus fuscus, how-
ever, has a greater flight speed than some
Myotis sp. (Patterson and Hardin, 1969)
and may have greater powers of dispersal
enabling pregnant females to fly farther
north in time to give birth and to rear their
young.

Myotis leibii is not known to occur north
of the — 18°C mean minimum January iso-
therm (Fig. 1) as drawn by Chapman and
Thomas (1968). Peterson (1966) reported
several specimens of E. fuscus from localities
north of this January isotherm; his records
are consistent with the suggested powers of
dispersal of this species and may also reflect
a greater flexibility of roosting habits relative
to M. leibii. The presence of M. leibii and
E. fuscus adjacent to Lake Superior could be
attributed to the warming effect of the lake
(Chapman and Thomas, 1968).

Sex Ratios — Percentages of males in winter-
ing populations of M. leibii and E. fuscus
are compared with data from other studies
(Table 1). Results obtained here agree with
those published elsewhere (Mohr, 1936;
Rysgaard, 1942; Hitchcock, 1965; and Phil-
lips, 1966). Male and female M. leibii were

encountered in almost equal numbers, but
male E. fuscus were more numerous than
females (Table 1). The incidence of male
E. fuscus in clusters (87%) was greater
than that for isolated individuals (53%) as
reported by Phillips (1966) for this species
and also for M. lucifugus (Fenton, 1970).

Hibernation Sites — Martin et al. (1966) re-
ported the occurrence of torpid M. leibii and
E. fuscus under rocks on the floor of mine
passages in Clinton County, New York, and
reviewed the few, similar reports for North
America. Although large numbers of M.
daubentonii hibernate under rocks in hiber-
nacula in Europe (Roer and Egsbaek,
1966), reports of bats hibernating under
rocks in North America have involved only
small numbers.

Thirty torpid E. fuscus, representing part
of a group of undetermined size, were found
in a pile of loose rock at the bottom of a
stope in the mine near Bryson, Quebec, on
22 March 1968. In an area where the am-
bient temperature was 3°C, bats were dis-
tributed throughout the loose rock and ag-
gregated in small groups of two or three.
These bats were still hibernating in the loose
rock on 23 April 1968 when the temperature
had risen to 4°C.

Allen (1962, p. 268), when referring to
the habit of M. leibii of hibernating in
crevices, suggested that "Perhaps their very

table 1. Percentages of male Myotis leibii and Eptesicus fuscus at eight hibernacula
(sample size in parentheses)

November December January February March April

Myotis leibii

Renfrew mine, Ontario

1966-1967

—

1967-1968

47(17)

Bonnechere cave, Ontario*

Eldorado mine, Ontario*

Eptesicus fuscus

Renfrew mine, Ontario

1966-1967

50(6)

Bryson mine, Quebec

70 (62)

Wakefield cave, Quebec*
Bonnechere cave, Ontario*
Leavenworth mine, Kansasf

45(9)

43 (14)

42 (12)

80 (10)

60 (10)

—

57 (41)

83 (23)

45(13)

45 (22)

50 (75)
53 (728)
37(51)

60 (20)

60 (20)

67(21)

20(5)

56 (86)

65 (269)

92 (79)

72 (410)
75 (94)
74(491)
64 (475)

* Hitchcock, 1965.
tPhillips, 1966.

N = 67(178)

Temperature

Figure 2

Temperatures at which Eptesicus fuscus (A), Myotis leibii (B),

and Myotis lucifugus (C) were found

in torpor. N = number of occurrences, with the number of bats shown in parentheses.

much smaller and more delicate feet may be
correlated with this habit." Martin et al.
(1966), however, disagreed with Allen and
suggested that the floor of a cave or mine
might be a cooler, more stable thermal zone
for hibernation than walls or ceilings. Their
suggestion is substantiated by my findings at
Bryson, for during the time that the tem-
perature changed from 3° to 4°C in the area
occupied by the E. fuscus, temperatures rose
from 6° to 8 °C in an adjacent area harbour-
ing torpid M. lucifugus.

Both these bats select cool sites for hiber-
nation (Mohr, 1936;Rysgaard, 1942; Hitch-
cock, 1949; and Hall, 1 962 ) . The tempera-
ture ranges over which torpid M. leibii, E.
fuscus, and M. lucifugus were found are
shown in Fig. 2. Myotis leibii and E. fuscus

tolerate colder temperatures (— 9°C) than
do M. lucifugus (— 4°C) without arousing
from torpor. My observations in the hiber-
nacula indicated that temperatures below
these levels stimulated arousal from torpor.
Data given here for arousal of bats from
torpor at subfreezing temperatures (viz. at
-9°C for M. leibii and E. fuscus and -4°C
for M. lucifugus) are similar to those ob-
tained by Davis and Reite (1967) for M.
lucifugus. Metabolic compensation by torpid
M. lucifugus exposed to subfreezing tem-
peratures may be energetically less expensive
than arousal (Davis, 1970), but only to a
certain temperature (— 4°C). The ability to
remain torpid at subfreezing temperatures
(not a uniform trait in the sample studied by
Davis and Reite, 1967) might be more com-

mon in those M. lucifugus that hibernate in
colder parts of the range of this species.

Data given here for E. fuscus (Fig. 2)
differ from published information indicating
that bats of this species arouse from torpor
at subfreezing temperatures and remain ac-
tive until the ambient temperature increases
(Davis and Reite, 1967). Davis (1970) dis-
cussed the adaptive value of arousal under
these conditions. He also noted that data
conflict with results of Swanson and Evans
(1936) indicating (as do those of Goehring,
1971) that E. fuscus remain torpid at sub-
freezing temperatures. Seasonal variation in
the ability to arouse from torpor at lower
temperatures (Menaker, 1962; Smalley and
Dryer, 1963) could account for these dis-
crepancies (Davis, 1970).

At subfreezing temperatures M. leibii and
E. fuscus may become supercooled (see
Davis and Reite, 1967; Davis, 1970), a
physiological state that may be energetically
less costly than metabolic compensation,
sensu Davis (1970). Davis and Reite (1967)
suggested that supercooling was a transient
condition. Lyman (1970), however, inter-
preted their data to indicate that super-
cooled bats only arouse when exposed to an
abrupt or gradual increase in temperature;
a decrease in temperature would not effect
arousal according to Lyman (1970). As M.
lucifugus, M. leibii, and E. fuscus in On-
tario aroused when ambient temperatures
dropped below their respective thresholds of
tolerance, either these bats were not in a
supercooled condition or previous sugges-
tions concerning supercooling need verifica-
tion.

Myotis leibii and E. fuscus enter hiber-
nacula late in autumn and are always the
first to depart in spring (late November to
early April at the Renfrew mine). During
warm periods in winter, when temperatures
at their hibernation sites rise above 4°C, bats
of these two species may arouse and depart
from caves and mines to occupy other hiber-
nation sites as yet unknown. This suggestion
is supported by the presence of torpid E.
fuscus at the mine near Bryson in May when
surface temperatures were above freezing.
Here bats hibernated deep in the mine (500
to 600 feet below ground level) in passages
containing considerable ice and with am-
bient temperatures below 4°C and were not

exposed to warmer temperatures and thus
did not arouse from torpor. These data for
M. leibii and E. fuscus support the hypo-
thesis of Martin et al. (1966) concerning the
selection of cool, thermally stable areas for
hibernation.

The number of species composing clusters
of torpid bats provides a further indication
of species-specific tolerances to tempera-
tures suitable for hibernation. I commonly
observed M. leibii hibernating in physical
contact with E. fuscus, usually in small
clusters (less than five bats). I also found
that E. fuscus hibernated in physical contact
with M. lucifugus, and once I found one E.
fuscus in the centre of a cluster of torpid
M. sodalis (Fenton, 1966). Torpid M. leibii
were never seen close to or in physical con-
tact with M. lucifugus or M. sodalis. These
observations indicate that E. fuscus may
tolerate a broader range of temperatures
during hibernation than do M. lucifugus or
M. leibii.

The absence of M. leibii and E. fuscus,
the species most tolerant of low tempera-
tures, from northern hibernacula is note-
worthy. Several bats known to hibernate in
exposed situations may withstand subfreez-
ing temperatures (e.g., Lasiurus borealis to
-26°C; Davis, 1970) and yet apparently do
not hibernate in regions of their ranges with
the coldest winter temperatures.

Changes in Weight during Hibernation —

Changes in body weight of M. leibii during
the winters of 1966-1967 and 1967-1968
at the Renfrew mine are shown in Fig. 3.
Weights of male and female M. leibii taken
from hibernation in December 1966 aver-
aged 5.6 g, but by April 1967 the mean
weight had decreased to 4.7 g, representing
a weight loss of 0.9 g ( 16% ). Body weights
of males were not significantly different from
those of females. An F test for linearity indi-
cated that a least squares regression analysis
between time and change in weight was not
significant.

Weights of male and female E. fuscus that
were torpid in November 1966 at the Ren-
frew mine averaged 21.6 g, but 157 days
later in April 1967, the mean weight was
16.4 g. During the winter 5.2 g (24%) of
the November weight were lost. Weights of
females were significantly greater than those

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23 13 22 N1967

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12 10 10 4 N 196(
iiii.

Nov

Dec

Jan

Feb

March

Apri

Figure 3

Changes in weight of Myotis leibii hibernating in the Renfrew mine during the winters of 1966-1967
and 1967-1968 as shown by Dice-Leraas diagrams. Males and females are combined in each sample.
Sample size is given below or above the diagrams.

of males (p = 0.05) ; moreover, females lost
weight at a slower rate. The relationship be-
tween time and change in weight was linear
(p = 0.05). These data are similar to those
of Beer and Richards (1956) for E. fuscus,
as shown by a comparison of the regression
lines from the two studies :

Beer and Richards (1956)
Males y = 20.59 - 0.0385x

Females y = 2 1 .49 - 0.0300x

This Study
Males y = 20.46 - 0.04x

Females y = 22.07 - 0.03x

The amount of weight lost during hiberna-
tion relative to the initial weight before
hibernation was similar in E. fuscus (24%)
and M. lucifugus (25% ; Fenton, 1970), but
the rate of weight loss was slower and the
duration of hibernation longer in the latter.
Loss of weight in M. leibii was proportionally
less than in M. lucifugus and E. fuscus.

Acknowledgments — I thank J. A. Dick, J. A.
Graham, G.W.J. Laidlaw, J. Reid, B. Rich-
ardson, B. Trevor-Deutsch, G.E. Turner,
J.G. Woods, and E. Worrall for assistance
with field work. Messrs P. Ebsworth, T.
Guiney, J. Hammel, and S. Tobias kindly

permitted access to their properties. I am
grateful to Drs. R.L. Peterson, G.R. Car-
mody, D.A. Smith, and J.R. Tamsitt for
critically reading the manuscript. The work
was initially supported by grants from the
National Research Council of Canada (nrc)
to Dr. R.L. Peterson of the Department of
Mammalogy, ROM, and the Department of
Zoology, University of Toronto, and recently
by nrc grants to the author.

Summary — Myotis leibii (= M. subulatus)
and Eptesicus fuscus occur along the north
shore of Lake Huron and the east shore of
Lake Superior in summer but are absent
from these areas in winter. In hibernating
populations of M. leibii, males and females
are almost equally numerous, whereas males
predominate in hibernating populations of
E. fuscus. Within hibernacula, both bats
were found torpid between —9° and 4°C.
Large numbers of E. fuscus hibernated in
loose rock on the floor of a mine passage in
Quebec. Both species lost weight continu-
ously during the winter. E. fuscus males
weighed significantly less than females
throughout the hibernation period and lost
weight at a faster rate.

Literature Cited

Allen, G.M.

1962 Bats. Reprint ed. New York, Dover Publications Cambridge, Mass., Harvard
University Press, 1939. 368 pp.
Allin. A.E.

1942 Bats hibernating in the District of Thunder Bay, Ontario. Can. Fid. Nat., vol. 56,
no. 6, pp. 90-91.
Beer, J.R. and A.G. Richards

1956 Hibernation of the big brown bat. J. Mammal., vol. 37, no. 1, pp. 31-41.
Chapman, L.J. and M.K. Thomas

1968 The climate of northern Ontario. Clim. Stud. Dep. Transp. Met. Brch. Can., no.
6, pp. 1-58.

Davis, W.H.

1970 Hibernation: Ecology and physiological ecology. In Wimsatt, W.A., ed. Biology of
Bats. Vol. 1. New York, Academic Press, pp. 265-300.
Davis, W.H. and O.B. Reite

1967 Responses of bats from temperate regions to changes in ambient temperature.
Biol. Bull. Mar. Biol. Lab., Woods Hole, vol. 132, no. 3, pp. 320-328.

Fenton, M.B.

1966 Myotis sodalis in caves near Water town, New York. J. Mammal., vol. 47, no. 3,
p. 526.

1969 Summer activity of Myotis lucifugus (Chiroptera : Vespertilionidae) at hibernac-
ula in Ontario and Quebec. Can. J. Zool. vol. 47, no. 4, pp. 597-602.

1970 Population studies of Myotis lucifugus (Chiroptera : Vespertilionidae) in Ontario.
Life Sci. Contr., R. Ont. Mus., no. 77, pp. 1-34.

Glass, B.P. and R.J. Baker

1968 The status of the name Myotis subulatus Say. Proc. Biol. Soc. Wash., vol. 81,
pp. 257-260.

Goehring, H.H.

1971 Big brown bat survives sub-zero temperatures. J. Mammal., vol. 52, no. 4, pp.
832-833.

Hall, J.S.

1962 A life history and taxonomic study of the Indiana bat, Myotis sodalis. Scient.
Pubis. Reading Publ. Mus., no. 12, pp. 1-68.
Hitchcock, H.B.

1949 Hibernation of bats in southeastern Ontario and adjacent Quebec. Can. Fid. Nat.,
vol. 63, no. 1, pp. 47-59.

1965 Twenty-three years of bat banding in Ontario and Quebec. Can. Fid. Nat., vol. 79,
no. 2, pp. 4-14.

Lyman, C.P.

1970 Thermoregulation and metabolism in bats. In Wimsatt, W.A., ed. Biology of bats.
Vol. lr New York, Academic Press, pp. 301-330.
Martin, R.L., J.T. Pawluck and T.B. Clancy

1966 Observations on hibernation of Myotis subulatus. J. Mammal., vol. 47, no. 2,
pp. 348-349.

Menaker, M.

1962 Hibernation-hypothermia: An annual cycle of response to low temperature in the
bat, Myotis lucifugus. J. Cell. Comp. Physiol., vol. 59, no. 3, pp. 163-173.
Mohr, C.E.

1936 Notes on the least brown bat Myotis subulatus leibii. Proc. Pa. Acad. Sci., vol.
10, pp. 62-65.
Patterson, A.P. and J.W. Hardin

1969 Flight speeds of five species of vespertilionid bats. J. Mammal., vol. 50, no. 1,
pp. 152-153.

Peterson, R.L.

1966 The mammals of eastern Canada. Toronto, Oxford University Press, 465 pp.
Phillips, G.L.

1966 Ecology of the big brown bat (Chiroptera : Vespertilionidae) in northeastern
Kansas. Am. Midi." Nat., vol. 75, no. 1, pp. 168-198.
Roer, H. and W. Egsbaek

1966 Zur Biologie einer skandinavischen Population des Wasserfledermaus (Myotis dau-
bentonii) (Chiroptera). Z. Saugetierk., vol. 31, pp. 440-453.
Rysgaard, G.N.

1942 A study of the cave bats of Minnesota with especial reference to the large brown
bat, Eptesicus fuscus fuscus (Beauvois). Am. Midi. Nat., vol. 28, no. 1, pp.
245-267.
Smalley, R.L. and R.L. Dryer

1963 Brown fat: Thermogenic effect during arousal from hibernation in the bat. Science,
vol. 140, no. 3573, pp. 1333-1334."
Swanson, G. and C. Evans

1936 The hibernation of certain bats in southern Minnesota. J. Mammal., vol. 17, no.
1, pp. 39-43.

Suggested citation: Life Sci. Occ. Pap., R. Ont. Mus.
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Sciences Editorial Board and to review by persons outside the Museum staff who are authorities in the
particular field involved.

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