2007 NORTHEASTERN NATURALIST 14(3):317–322
Food Habits of Myotis leibii during Fall Swarming in
West Virginia
Joshua B. Johnson1,* and J. Edward Gates1
Abstract - The ecology of Myotis leibii (eastern small-footed myotis) remains largely
unclear, including its foraging behavior. During fall, cavernicolous bats must accumulate
enough fat reserves to sustain them during winter hibernation. We examined the
food habits of eastern small-footed myotis captured at abandoned coal mines at New
River Gorge National River in West Virginia during fall 2005. Based on fecal samples
from 44 bats, we found that eastern small-footed myotis diets were diverse, containing
9 families within 7 orders of insects. Lepidoptera were consumed by all but one bat and
represented the largest average percent volume among insect orders. This study
elucidates an important component of the foraging ecology of this rare bat species.
Introduction
Myotis leibii Audubon and Bachman (eastern small-footed myotis) is
considered rare throughout its range, which includes northern Arkansas and
southern Missouri, east to the Appalachian Mountains and Ohio River basin,
and north into New England, southern Ontario, and Quebec (Barbour and
Davis 1969, Best and Jennings 1997). Although the causes of its rarity are
unclear, it is suspected that low over-winter survival rates may be a factor
(Hitchcock et al. 1984). During winter, eastern small-footed myotis hibernate
in colder portions of mines and caves, where they sometimes are found
in crevices and under rock slabs (Davis and Lidicker 1955, Gates et al. 1984,
Martin et al. 1966). Anecdotal observations indicate eastern small-footed
myotis roost in mines, caves, and rock outcrops during summer (Best and
Jennings 1997, Hall and Brenner 1968), and are rarely associated with
buildings (Hitchcock 1955). In late summer and early fall, eastern smallfooted
myotis and sympatric cavernicolous bat species arrive at cave and
mine entrances and exhibit swarming behavior. Swarming is thought to
fulfill particular life-history requirements such as mate selection, breeding,
and hibernacula selection (Cope and Humphrey 1977, Fenton 1969,
Schowalter 1980). During this time period, bats accumulate fat reserves vital
to surviving hibernation (Ewing et al. 1970, Fleming and Eby 2003, Krulin
and Sealander 1972, Tuttle 1976).
Little is known about the food habits of eastern small-footed myotis. To our
knowledge, the only published record of food habits of eastern small-footed
myotis examined fecal samples of 4 individuals captured at caves in western
Maryland (McDowell-Griffith 1983). We examined the food habits of eastern
1University of Maryland Center for Environmental Science, Appalachian Laboratory,
301 Braddock Road, Frostburg, MD 21532. *Corresponding author -
jjohnson@al.umces.edu.
318 Northeastern Naturalist Vol. 14, No. 3
small-footed myotis during fall swarming because little is known about this
aspect of its ecology, despite the importance of preparing for hibernation.
Study Area and Methods
We conducted bat surveys at abandoned coal mines at New River Gorge
National River (NERI) in Fayette County, WV. NERI contains approximately
28,329 ha located in the Appalachian Plateau physiographic province
(Fenneman 1938) and is characterized by steep slopes and exposed rock cliffs
ascending 300 m above the river to plateau-like ridge tops. The New River
courses through NERI and is provisioned by high-gradient streams that incise
the steep slopes of the gorge. Quercus spp. (oaks) dominate the forest overstory,
while the understory mainly consists of Rhododendron maximum
Linnaeus (rhododendron). The abandoned mine portals at NERI are used by
many bat species, including Corynorhinus rafinesquii Lesson (Rafinesque’s
big-eared bat), C. townsendii virginianus Cooper (Virginia big-eared bat),
Eptesicus fuscus Beauvois (big brown bat), eastern small-footed myotis, M.
lucifugus LeConte (little brown myotis), M. sodalis Miller and Allen (Indiana
myotis), M. septentrionalis Trouessart (northern myotis), and Perimyotis
subflavus Cuvier (eastern pipistrelle) (Johnson et al. 2005, 2006).
We surveyed for bats at 19 NERI mine entrances during fall 2005 (22
August to 29 September). We used 1-m2 harp traps (Bat Conservation and
Management, Carlisle, PA) and/or mist nets (6 x 2.8 m or 9 x 2.8 m, depending
on entrance size; Avinet, Dryden, NY) to capture bats entering or exiting the
mines or swarming around mine entrances. Harp traps were positioned in mine
entrances and were surrounded with tarpaulin to prevent bats from bypassing
the harp trap. We positioned mist nets 1–2 m from mine entrances, if harp traps
were not used. Depending on their proximity, 1–3 mine entrances were
sampled each night. We sampled each mine entrance 3 nights (once in August,
early September, and late September, respectively) between sunset and 0000
hours, with at least 9 nights separating consecutive samples.
Data collected from each captured bat included species (Menzel et al.
2002), sex, age, and reproductive condition (Anthony 1988, Racey 1988). The
reproductive condition of females and the ages of all bats were difficult to
determine during fall sampling and were not considered during analyses. We
uniquely marked their wings with non-toxic paint markers to facilitate identification
of recaptures within the same night (Barclay and Bell 1988). Bat
recaptures at caves or mines during fall swarming are typically less than 5% within the
season (Fenton 1969, Marsh 1998). We placed captured eastern small-footed
myotis in plastic containers for 10 minutes or until fecal samples were
obtained. Sampled bats and those that did not void feces within 10 minutes
were released unharmed. Fecal samples were frozen until analysis. Bat capture
and handling protocols were approved by the Institutional Animal Care and
Use Committee of the University of Maryland Center for Environmental
Science (Protocol Number F-AL-05-06) and followed the guidelines of the
American Society of Mammalogists (Animal Care and Use Committee 1998).
2007 J.B. Johnson and J.E. Gates 319
We used a 20–40x dissection microscope to examine fecal samples, which
were placed in a petri dish and teased apart into a uniform layer in 70%
isopropyl alcohol (Whitaker 1988). To facilitate insect identification, we used
a reference insect collection and referred to dichotomous keys and figures in
texts (e.g., Triplehorn and Johnson 2005, Whitaker 1988). We identified
insects to order, and superfamily or family when possible. We followed the
insect taxonomic classification system in Triplehorn and Johnson (2005). We
visually estimated percent volume of each insect order in each sample by backlighting
a transparent 1-mm2 grid beneath the petri dish (Whitaker 1988). We
estimated percent volume of Lepidoptera according to Whitaker (1988) and a
bat food-habits study in West Virginia (Carter et al. 2003). We calculated
average percent volume and percent frequency of prey items for the dataset.
The average percent volume was the average percentage by volume of each
insect type in the total sample. This measure is useful for determining if, on
average, certain insect types comprise a large portion of bat species’ diets. The
percent frequency was the number of bats consuming each insect type divided
by the total number of sampled bats (Whitaker 1988). This measure determines
if consumption of a certain insect type is widespread among individuals of a bat
species. Together, average percent volume and percent frequency can be used
to examine if few individuals of a bat species are consuming a particular insect
type or if they are more general in their prey preference.
Results
We captured 84 eastern small-footed myotis, including 66 males and 17
females, at 18 mine entrances throughout the sampling period. One eastern
small-footed myotis escaped before sex was determined. Fecal samples were
obtained from 44 eastern small-footed myotis, including 39 males and 5
females. We identified 7 insect orders, 1 superfamily, and 9 families in the
fecal samples. Lepidoptera (moths) were the most frequently consumed insect
order and were more abundant, on average, than any other consumed
insect order (Table 1). Other insect orders (superfamilies or families) we
identified included Hymenoptera (Chalcidoidea and Ichneumonidae, parasitic
wasps), Coleoptera (Curculionidae, snout beetles; and Scarabaeidae, scarab
beetles), Diptera (Mycetophilidae, fungus gnats; Psychodidae, moth flies; and
Tipulidae, crane flies), Psocoptera (Psocidae, common barklice), Hemiptera
(Cercopidae, froghoppers), and Neuroptera (Hemerobiidae, brown lacewings).
We observed soil particles or small gravel from 3 bats.
Table 1. Insect orders found in fecal samples of Myotis leibii (n = 44) at New River Gorge
National River, WV, 2005. Lep = Lepidoptera, Dip = Diptera, Col = Coleoptera, Hym =
Hymenoptera, Pso = Psocoptera, Neu = Neuroptera, and Hem = Hemiptera.
Insect order
Lep Dip Col Hym Pso Neu Hem
Percent volume 58.5 24.7 5.5 5.4 3.4 1.6 1.0
Percent frequency 97.7 65.9 45.5 27.3 15.9 6.8 4.5
320 Northeastern Naturalist Vol. 14, No. 3
Discussion
Eastern small-footed myotis consumed a variety of insects at NERI, and
consumed more Lepidoptera, by volume and frequency, than other insect
orders. These results were similar to data collected in fecal samples from
eastern small-footed myotis captured during a study of food habits of bats in
western Maryland (McDowell-Griffith 1983). Other myotine bats, including
little brown myotis and northern myotis, in West Virginia also are known to
consume a variety of insects (Burke 2002, Carter et al. 2003). Burke (2002)
found that little brown myotis and northern myotis consumed mostly Lepidoptera,
in volume and frequency. Carter et al. (2003) determined that little
brown myotis consumed mostly Lepidoptera, and northern myotis consumed
mostly Coleoptera. Differential digestion of different insect orders by bats
may introduce some error into fecal analysis results (Kunz and Whitaker
1983). For example, although Lepidoptera apparently are an important food
source for eastern small-footed myotis, scales from Lepidoptera may persist
in the bat’s digestive system for several days, increasing the frequency of
occurrence compared to other insects whose undigested parts may be voided
within hours after consumption (Buchler 1975, Whitaker 1988). Moreover,
comparing percent-by-volume may overestimate the importance of Lepidoptera
because small, hard-bodied prey items contribute little to the total
volume (Griffith and Gates 1985, Kunz and Whitaker 1983). For example,
although Coleoptera were present in >45% of our samples, they represented
<6% of the total volume. Lepidoptera often comprised the remainder of the
sample volume not occupied by identifiable hard-bodied insect parts. However,
among all the insect orders, only Lepidoptera ever comprised 100% of a
sample, which we observed five times, supporting the suggested importance
of Lepidoptera to eastern small-footed myotis.
It is unclear why soil particles or small gravel were ingested by 3 bats in
our study. Soil has been found in fecal samples collected from big brown
bats, little brown myotis, northern myotis, and eastern pipistrelles in western
Maryland and New York (Buchler 1976, McDowell-Griffith 1983). The
authors suggested that these bats ingested soil with insect prey captured
from the ground. The high-frequency, broadband, frequency-modulated
echolocation call of eastern small-footed myotis may be suited for gleaning
prey from substrates (Mukhida et al. 2004). Eastern small-footed myotis
have been observed foraging near the forest floor (van Zyll de Jong 1985).
Perhaps eastern small-footed myotis in our study consumed soil when capturing
insect prey from the ground or during grooming while roosting in the
mines. It is unknown if consumed soil particles provide any nutritional
benefit to the bats or aid in mechanical digestion of chitin.
Our study reveals an important component of the foraging ecology of
eastern small-footed myotis. Food habits of eastern small-footed myotis
were poorly documented prior to our study. We found that eastern smallfooted
myotis consumes a variety of insects, but may specialize in preying
upon Lepidoptera. It is unclear if our results are representative of food
2007 J.B. Johnson and J.E. Gates 321
habits of eastern small-footed myotis in other areas of its range or during
other seasons because of the paucity of existing data. Many important
aspects of eastern small-footed myotis ecology remain undetermined. Further
research focusing on food preferences and availability, and foraging
habitat of eastern small-footed myotis is warranted and will help facilitate
the conservation of this rare species.
Acknowledgments
We thank the National Park Service-New River Gorge National River for providing
housing and assistance during the field season. We appreciate the hard work of G.
Clare, L. Hindson, K. Lott, J. Perez, A. Sherman, and K. Zielinski. T. Carter provided
valuable advice concerning fecal analysis. The NPS Inventory and Monitoring Program
- Eastern Rivers and Mountains Network provided funding. This article is
Scientific Contribution Number 4017 of the University of Maryland Center for
Environmental Science, Appalachian Laboratory.
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