Rediscovery, ecology, and identification of rare free-tailed bats (Chiroptera: Molossidae) in Costa Rica

Abstract

Five new specimens of the poorly known Sanborn's bonneted bat, Eumops hansae (Chiroptera: Molossidae), are reported for Costa Rica's central and northern Pacific lowlands based on a subadult male collected in 1990 and four adult females collected in 2003. We also report the second known specimen of Eumops underwoodi from Costa Rica and additional specimens of Cynomops mexicanus, Eumops glaucinus, Molossus molossus, and Molossus pretiosus. Most of the females captured in August and April were either lactating or pregnant, suggesting that parturition in these molossids occurs in the late dry season and the early to middle rainy season, periods when insects are especially abundant in this dry forest. Characters used previously to distinguish between the similar-sized E. hansae and E. nanus are evaluated, and external and cranial measurements for the specimens of E. hansae are provided. The best single character for distinguishing the two species is size and shape of the upper incisors. In E. hansae, the upper incisors are thin and recurved, whereas they are thick, straight, and slightly procumbent in E. nanus. The six sympatric species of free-tailed bat found in the gallery forest along the Río Enmedio vary in size, jaw thickness, and wing shape suggesting coexistence through resource partitioning in this molossid bat assemblage.

Full text

INTRODUCTION
Twelve species of free-tailed bats (Chiroptera:
Molossidae) are known from Costa Rica, although
little is known about the biology of any of these
species in the country (Timm and LaVal, 1998;
Rodríguez-H. and Wilson, 1999; Timm et al., 1999;
LaVal and Rodríguez-H., 2002). Among the most
poorly known New World molossids are the bonnet-
ed bats of the genus Eumops, a monophyletic line-
age of 12–13 species: E. auripendulus, E. bonarien-
sis, E. dabbenei, E. floridanus, E. glaucinus,
E. hansae, E. maurus, E. nanus, E. patagonicus,
E. perotis, E. trumbulli, E. underwoodi, and un -
described species from western Ecuador (Eger,
1977; Freeman, 1981; Koopman, 1993, 1994;
Gregorin and Taddei, 2002; Timm and Genoways,
2004; Gardner, 2008; McDonough et al., In press).
One of the most poorly known species in the ge-
nus is Eumops hansae. Sanborn (1932) described
the species based on a single adult male collected
in 1901 at Colonia Hansa, near Joinville, Santa
Caterina, Brazil. In subsequent years, few speci-
mens of this small free-tailed bat have been collect-
ed from widely scattered localities in Central and
South America, including southern Chiapas, Méx -
ico, northern Honduras, southwestern Costa Rica,
and eastern Panamá in Central America and in South
America from the Guiana region to Argentina (Reid,
1997; Best et al., 2001). Specimens are known from
elevations ranging from 45 to 600 m.
Eumops hansae was known previously from
Costa Rica on the basis of only a single specimen
(LSUMZ 11487) collected on the Osa Peninsula in
the southwestern Pacific lowlands in 1966 by A. B.
McPherson (Gardner et al., 1970). The adult male
was captured in a net set across a stream in an area
of tropical moist forest 10 km south of Palmar Sur,
Puntarenas Province, at 600 m. Despite extensive
netting throughout the country in the intervening
years, no additional records of E. hansae have been
reported.
Acta Chiropterologica, 10(1): 97–102, 2008
PL ISSN 1508-1109 © Museum and Institute of Zoology PAS
doi: 10.3161/150811008X331135
Rediscovery, ecology, and identification of rare free-tailed bats
(Chiroptera: Molossidae) in Costa Rica
WILLY PINEDA1, 4, BERNAL RODRÍGUEZ-HERRERA1, 2, and ROBERT M. TIMM3
1Asociación para la Conservación de los Murciélagos de Costa Rica, 12671-1000 San José, Costa Rica
2Instituto de Ecología, Universidad Nacional Autónoma de México, 70-275, México D.F. 04510, Mexico
3Natural History Museum and Biodiversity Research Center & Department of Ecology and Evolutionary Biology,
University of Kansas, Lawrence, Kansas 66045, USA
4Corresponding author: E-mail: wpineda@tirimbina.org
Five new specimens of the poorly known Sanborn’s bonneted bat, Eumops hansae (Chiroptera: Molossidae), are reported for Costa
Rica’s central and northern Pacific lowlands based on a subadult male collected in 1990 and four adult females collected in 2003.
We also report the second known specimen of Eumops underwoodi from Costa Rica and additional specimens of Cynomops
mexicanus, Eumops glaucinus, Molossus molossus, and Molossus pretiosus. Most of the females captured in August and April were
either lactating or pregnant, suggesting that parturition in these molossids occurs in the late dry season and the early to middle rainy
season, periods when insects are especially abundant in this dry forest. Characters used previously to distinguish between the similar-
sized E. hansae and E. nanus are evaluated, and external and cranial measurements for the specimens of E. hansae are provided.
The best single character for distinguishing the two species is size and shape of the upper incisors. In E. hansae, the upper incisors
are thin and recurved, whereas they are thick, straight, and slightly procumbent in E. nanus. The six sympatric species of free-tailed
bat found in the gallery forest along the Río Enmedio vary in size, jaw thickness, and wing shape suggesting coexistence through
resource partitioning in this molossid bat assemblage.
Key words: Costa Rica, Molossidae, bonneted bats, identification, Eumops hansae

98 W. Pineda, B. Rodríguez-Herrera, and R. M. Timm
Recent reviews suggest that E. underwoodi oc-
curs from the extreme southwestern United States
and western México to Honduras (Lee and Bradley,
1992; Kiser, 1995; Reid, 1997). However, Foster
and Aguilar (1993) reported a single individual
found dead in Costa Rica’s lowland tropical dry for-
est at Cañas. There have been no subsequent reports
of E. underwoodi occurring either in Costa Rica or
neighboring Nicaragua.
Our recent fieldwork in northwestern Costa Rica
and study of museum specimens led to the collection
and identification of several poorly known molos-
sids. Here, we report these species and provide per-
tinent ecological information and external and cra-
nial measurements. Additionally, we expand the
original description of the species E. hansae and
make comparisons between E. hansae and the simi-
lar-sized E. nanus.
METHODS AND MATERIALS
On 18 August 2003, one of us (WP) set two mist nets
(2 × 10 m) across the Río Enmedio in a V-shaped pattern at
Refugio Nacional de Vida Silvestre Bosque Nacional Diría
(10°10’24”N, 85°35’39”W, 128 m a.s.l.), 11 km southwest of
Santa Cruz, Guanacaste Province, Costa Rica. The nets were
open from 18:00 h to 19:35 h. One net extended from the dry
riverbed over rocks and sand to the middle of the river and the
other from this point over shallow water (60 cm deep) to the
other riverbank. WP returned to this site on 18 April 2004 and
set two mist nets in the same positions from 18:00 h to 21:00 h.
The river is ca. 40 m wide here and surrounded by gallery for-
est with trees 30 m tall, including Anacardium excelsum, Ceiba
pentandra, Ochroma pyramidale, and low shrubs. Costa Rica’s
northwestern Pacific lowlands are characterized by tropical dry
forest, with a pronounced dry season from November to May,
and a rainy season from June to October (1,000–2,000 mm).
Most of the Central American dry forest has been cleared; low-
land areas are especially subjected to intense agriculture and ex-
tensive livestock use (Mata and Echeverría, 2004). The gallery
forest along the Río Enmedio is one of the few such tracts of in-
tact forest remaining.
Forearms (FA) and crania of specimens collected in these
field trips were measured by RMT with dial calipers to the near-
est 0.1 mm. External measurements, other than forearm length,
are those recorded on specimen labels by collectors, as are testis
measurements. The following cranial measures were taken:
greatest length of skull, condylobasal length, zygomatic
breadth, postorbital constriction, mastoid breadth, length of
maxillary toothrow, greatest alveolar breadth of upper canines
(C–C), and breadth across crowns of upper molars (M3–M3).
Greatest length of skull includes incisors; measurements of the
maxillary toothrow are of the greatest alveolar length and fore-
arms were measured from the proximal extension of the ra-
dius–ulna (elbow) to the distalmost extension of the carpals
(flexed wrist). We provide for comparison between E. hansae
and E. nanus, external and cranial measurements for 4 adult fe-
males, and the previously reported adult male E. hansae from
Costa Rica, an adult male E. nanus from Nicaragua and an adult
female from Panama (Table 1). We follow Peters et al. (2002) in
recognizing Cynomops mexicanus as the correct name for the
dog-faced bats of the lower Central American dry forest.
Eight bats captured in August 2003 were retained as vouch-
ers and deposited as skins and skulls in the collection of the
Museo Nacional de Costa Rica: 2 XX Cynomops mexicanus
(MNCR 1490–1491), 3 XX E. hansae (MNCR 1488–1489,
MNCR 1494), 1 XE. underwoodi (MNCR 1487), and 2 YY
Molossus pretiosus (MNCR 1492–1493). Dietary data for each
bat species were studied using Petri dishes where the stomach
contents were dissolved and dispersed homogenously with alco-
hol; the insect remains per bat species were identified to the
lowest taxonomic level possible and their abundance estimated
qualitatively.
RESULTS
In August 2003, 23 individuals of five species of
molossids were captured in nets set across the Río
Enmedio. They include: Cynomops mexicanus (3
adult ♀♀; all lactating), E. hansae (4 adult ♀♀; all
lactating), E. underwoodi (1 adult ♀; lactat ing), Mo -
lossus molossus (1 adult ♀; lactating), and M. pre-
tiosus (4 adult ♂♂ and 10 adult ♀♀; 7 lactating,
2 others pregnant). All individuals but one were
caught in the net set over shallow water and the ma-
jority (83%) captured on the upstream side of the
nets. These are the first records of E.hansae from
the Central American tropical dry forest and extend
the geographic distribution 300 km northwest from
the only previously known locality in Costa Rica.
This is the second record of E. underwoodi from
Costa Rica; both are from the dry forest. The single
E. underwoodi from Bosque Diría was an adult
lactating female (FA = 72 mm), and provides docu-
mentation that the species breeds in Costa Rica.
While this bat was being handled in the mist net,
it emitted loud vocalizations that were audible to the
human ear. In apparent response, another large bat
flew over the net in two or three fast passes, suggest-
ing that it was responding to the calls.
In April 2004, two nets set at the same site were
used to capture 10 individuals of three species of
molossids: C.mexicanus (6 adult ♀♀; all lactating),
Eumops glaucinus (1 adult ♂), and M. pretiosus
(3 adult ♀♀; 2 lactating, 1 pregnant); all individuals
were caught in the net set over shallow water. This
is the first record of E. glaucinus from the tropical
dry forest in Costa Rica. Other species captured
were: 1 Rhyncho nycteris naso, 1 Noctilio leporinus,
1 Pteronotus gymnonotus, 1 Chrotopterus auritus,
2 Micronyc teris hirsuta, 2 Carollia perspicillata,
1 C. subrufa, 2 Glossophaga soricina, 1 Artibeus
phaeotis, 1 Pla tyrrhinus helleri, 8 Sturnira lilium,
and 2 Uroderma bilobatum.

Food items found in August in the stomachs of
these free-tailed bats include the following:
E. hansae — Coleoptera and Diptera (Tipulidae);
E. underwoodi — Hymenoptera (Formicidae) and
possibly Neuroptera; C. mexicanus — Coleoptera,
Hemiptera, and Hymenoptera (Formicidae); and
M. pretiosus — Coleoptera, Hemiptera, and Hyme -
no ptera (Formicidae). Winged ants (Hymenoptera,
Formicidae) were the most abundant food items in
C. mexicanus, E. underwoodi, and M. pretiosus,
sug gesting that these bats feed opportunistically on
winged ants when they are abundant.
DISCUSSION
The published descriptions of E. hansae can be
expanded upon based on our comparisons of the
Costa Rican specimens from the Pacific lowlands
with other populations. Sanborn (1932: 356), in his
description of E. hansae, made direct comparisons
of the single adult male available to him to speci-
mens of the similar-sized E. nanus, noting that the
upper incisors of E. hansae have the tips widely sep-
arated and the lower incisors “are not bunched, but
are almost in a straight line, the outer about half the
size of the inner.” [Upon direct comparison, all spec-
imens of E. hansae are larger than the species we
now recognize as E. nanus] Gardner et al. (1970:
726) provided the following comparisons to distin-
guish E. hansae from E. nanus: “color darker; upper
incisors with widely separated tips; lower incisors
less crowded and almost in a straight line; . . . palate
ex tending behind the last molars; basisphenoid pits
conspicuously large, deep, and well defined.” Reid
(1997: 168) described the pelage of all Central
Amer ican molossids, noting characteristics of each.
She characterized E. hansae as “Upperparts dark
brown or blackish, hair dark to base … underparts
dark gray-brown, slightly paler than upperparts” and
E. na nus as, “Upperparts gray-brown or brown, base
of hair pale; underparts gray-brown, tips of hairs
frosted.”
In comparing E. hansae from Costa Rica to an
adult male and female E. nanus from Nicaragua and
Panama, respectively, we noted that the upper inci-
sors are widely separated at the tips in E. hansae,
whereas they converge in E. nanus. Additionally,
the incisors are thin and slightly curved in E. han -
sae, almost hooklike, whereas they are thick and
somewhat procumbent in E. nanus. The size and
shape differences in the upper incisors of these two
species have not been noted previously. The ba-
sisphenoid pits are ovoid and deep in E. hansae, and
proportionally deeper and longer than in E. nanus.
Rare free-tailed bats in Costa Rica 99
Total Tail Length Length Body Greatest Condylo- Zygomatic Post- Mastoid Length Breadth
Specimens Sex length length of hind of ear
Length Length
mass length of basal breadth orbital breadth of upper across
foot of tragus of forearm skull length constriction toothrow M3–M3
E. hansae (Costa Rica)
LSUMZ 11487* ♂ – – – – – 40.2 – 20.7 19.4 11.7 4.2 10.6 7.5 8.2
MNCR 1488 ♀ 102 35 9 17 2 36.8 – 18.5 17.8 10.6 3.8 10.0 6.6 7.6
MNCR 1489 ♀ 98 38 8 18 2 35.8 – 18.3 17.4 10.7 4.0 9.7 6.8 7.8
MNCR 1494 ♀ 100 35 9 16 2 36.4 – 18.8 17.5 10.6 3.8 9.9 6.7 7.4
E. nanus (Nicaragua)
KU 114142 ♂ 92 31 10 15 – 38.8 – 17.1 15.7 10.3 4.1 9.7 6.2 9.6
E. nanus (Panama)
USNM 331971 ♀ 86 28 7 12 – 39.4 8 16.7 15.1 9.6 3.5 – 5.9 7.2
* — data from Gardner et al. (1970)
TABLE 1. External and cranial measurements (in mm) and body mass (in g) of E. nanus and E. hansae from Central America. Acronyms used are: LSUMZ: Museum of Zoology, Louisiana
State University, MNCR: Museo Nacional de Costa Rica, KU: Museum of Natural History, Kansas University, USNM: United States National Museum of Natural History, Smithsonian
Institution

The palate in both E. hansae and E. nanus extends
posteriorly to just beyond the last molar, contrary to
what has appeared in the literature. The cranium,
when viewed laterally, is more bulbous in E. hansae
than in E. nanus. In E. nanus, the profile of the skull
is nearly flat. The pelage characters suggested by
Reid (1997: 168) for distinguishing E. hansae from
other molossids include upper parts dark brown, hair
dark to base, and underparts paler than upperparts.
The most definitive characters to distinguish
E. hansae from E. nanus other than size are the up-
per incisors, with those of E. hansae being thin,
widely separated at the tips, and slightly recurved
inward, whereas those of E. nanus converge distal-
ly, are considerably more massive, and are some-
what procumbent. Use of the combination of pelage
characters provided by Reid (1997) and cranial char-
acters provided herein should facilitate identifica-
tion of the two species in the field as well as in mu-
seum collections.
Eumops nanus has been reported previously
from Costa Rica on the basis of three specimens,
two from the Caribbean lowlands and one from the
Pacific lowlands (Rodríguez F. and Chinchilla,
1996). We have searched extensively for these spec-
imens in the collection of the Universidad de Costa
Rica (as well as in other collections) and have not
been able to locate them to reconfirm the identifica-
tions. They are cataloged in the Universidad de
Costa Rica collection with the following localities:
Limón Province, Parque Nacional Cahuita (UCR-
175, UCR-515) and Puntarenas Province, Parrita,
Isla Palo Seco (UCR-785). We concur with Eger
(2008) in recognizing E.nanus as representing
a species level taxon different from E. bonariensis,
E. delticus, and E. patagonicus. Eger (1977) treated
both delticus and nanus as subspecies of E. bona -
riensis, and recognized that there were morphologi-
cal differences between these taxa. Eumops nanus is
now known to occur in southern Mexico, throughout
Central America, and in northwestern South Amer -
ica (Eger, 2008).
Eumops underwoodi is a rare species throughout
its range (Reid, 1997), and it is considered (in addi-
tion to M. pretiosus, another species captured) en-
demic to the dry forest (LaVal, 2004), one of the
most endangered ecosystems in the Neotropics.
Foster and Aguilar (1993) reported this species in
Costa Rica based on a single young male (LACM
47106) found dead in the lowland Guanacaste dry
forest in 1974.
Of the 18 female molossids captured in north-
western Costa Rica in August, 17 were either
lactating or obviously pregnant, and in April, all
females were lactating or pregnant. Parturition
occurs in both the late dry season and in the early
and middle rainy season when insects are especial -
ly abundant (Janzen, 2004). From the reproductive
data taken in the rainy and dry seasons, at least two
species, C. mexicanus and M. pretiosus, give birth in
both seasons, an unusual reproductive pattern in
molossids. LaVal and Finch (1977) found pregnant
female M. pretiosus primarily in May and June, with
a lesser number in October. Our data suggest that
most of these molossids reproduce in both seasons,
but there are almost certainly some species which
reproduce only once a year. The beginning of
the rainy season in Costa Rica’s dry forest cor-
responds to a striking increase in insect diversity
and abundance resulting from a combination of the
emergence of adults that had been hidden in moist
microhabitats, maturation of adults from pupae in
cocoons or the soil, and migrating of adults from
cloud forest and rain forest (Janzen, 2004). Winged
ants (e.g., Atta cephalotes) can be found in great
numbers and fly high during their mating flights in
the rainy season in the tropical dry forest (Stevens,
1983).
Freeman (1981) predicted that the coexistence
of several species of molossids was possible based
on three attributes: differences in size (as assessed
by greatest skull length), food preferences (as as-
sessed by jaw thickness), and shape of wings (broad
or narrow). She combined these attributes in a mor-
phological niche matrix of exclusive cells occupied
by different species of the molossid assemblage al-
lowing resource partitioning in order to avoid com-
petition. Interestingly, the molossid bat assemblage
at Bosque Diría corresponds to Freeman’s (1981)
predictions about mechanisms of coexistence of
sympatric molossid bats. At Bosque Diría, we found
two large, narrow-winged species with a moder -
ately thick jaw (E. glaucinus and E. underwoodi),
two medium-sized, narrow-winged species with
moderately thick jaws (C. mexicanus and E. han -
sae), and two medium-sized, narrow-winged spe-
cies with thick jaws (M. molossus and M. pretio-
sus). Thus, these six sympatric species of molossids
correspond to three different cells in this morpho-
logical matrix and differ in jaw thickness and size,
suggesting that this free-tailed bat assemblage
shows relative resource partitioning in these two
aspects.
Bats of the genus Eumops are generally consid-
ered to be rare or uncommon in Central America;
however, they are probably much more common
100 W. Pineda, B. Rodríguez-Herrera, and R. M. Timm

than collection records indicate because they fly
relatively high and hence are rarely netted. Richard
K. LaVal (personal communication) detected vari-
ous species of Eumops at 32 of the 43 localities
sampled throughout Costa Rica during recent
acoustical surveys using the Anabat bat-detecting
system (Titley Electronics, Ballina, New South
Wales, Australia). Some of these localities are as
high as 1,500 m a.s.l. Unfortunately, identifica-
tion of Eumops to species with Anabat data files is
not possible at this time. Because it is likely that
E. han sae and E. nanus are found sympatrically, es-
pecially in the Pacific lowlands of Central America,
it is imperative that researchers undertaking ecol-
ogical studies correctly identify these similar sized
species. Given the difficulty in identification of
these species and the possibility of as yet unrecog-
nized species in the genus Eumops, voucher speci-
mens need to be taken and deposited in an approved
museum.
In a key to the Brazilian bats, Gregorin and
Taddei (2002) recently provided characters to distin-
guish between E. bonariensis, E. hansae, and
E. patagonicus, and Eger (2008) published a key to
all of the currently recognized Central and South
American species. Whether the populations as-
signed to E. hansae in Central America are truly
conspecific with those of Brazil near the type local-
ity remains an open question and we suspect that
they will in fact be recognized as separate species
upon future study. Additional work on distributions,
abundance, and natural history of Central American
molossids is critically needed. Many species are
difficult to distinguish both morphologically and
acoustically and a deeper knowledge on taxonomy
also is needed in this group.
ACKNOWLEDGEMENTS
The Ministerio del Ambiente y Energía (MINAE) and
Sistema Nacional de Áreas de Conservación (SINAC) provided
the opportunity to undertake our research on Costa Rican bats;
we especially thank reserve administrator F. Murillo and the
staff of the Reserve for their support and cooperation and Javier
Guevara S. for facilitating our research permits. We thank Mark
S. Hafner and Jessica E. Light, Museum of Natural Science
(LSUMZ), Louisiana State University, Baton Rouge, for provid-
ing us with a loan of critical specimens and information relating
to their capture; Alfred L. Gardner (USNM) for a critical discus-
sion of characters and species relationships; James Dines, Los
Angeles County Museum (LACM), Los Angeles assisted us on
several occasions with specimens housed in that collection. Paul
Hanson kindly assisted us in the identification of insect remains.
The manuscript benefited by suggestions from Joaquin Arroyo-
Cabrales, Alfred L. Gardner, Richard K. LaVal, Philip Myers,
and Heather A. York.
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Received 15 August 2007, accepted 01 January 2008