FIRST RECORD OF
MOLOSSUS MOLOSSUS TROPIDORHYNCHUS GRAY (1839) FROM
THE UNITED STATES
PHILIP A. FRANK
Florida Game and Fresh Water Fish Commission, Florida Keys Field Office,
2796 Overseas Highway, Suite 213, Marathon, FL 33050
Three colonies of Molossus molossus tropidorhynchus have been located in the Florida
Keys; one on Vaca Key, one on Boca Chica Key, and one on Stock Island. A single
specimen and several reports of bats suggest Key West as an additional locality. All colonies
were found in large buildings. Sizes of colonies were estimated to be 268 individuals on
Boca Chica and 70-100 individuals on Vaca Key. Colonization of the Keys occurred either
naturally via overwater dispersal or through introduction by humans, possibly from Cuba.
These records represent the first record of M. m. tropidorhynchus in the United States and
the first well-documented colonies of bats on the Florida Keys.
Key words:
Molossus molossus, Florida Keys, distribution
Molossus molossus is a small insectivorous bat that is widely distributed from
southern South America, north through
Central America and northern Mexico, and
through the Greater and Lesser Antilles, including Cuba (Eisenberg, 1989; Hall,
1981). It generally is common where it occurs, and uses a wide range of habitat types
including tropical dry deciduous and moist
forests (Eisenberg, 1989). M. m. tropidorhynchus occurs in Cuba, where it is abundant and widespread (Silva Taboada, 1979).
The Spanish common name, "murcielago
casero," reflects its preference for roosting
in houses, although natural tree roosts also
have been recorded (Silva Taboada, 1979).
Colonies in man-made structures commonly are located in restricted spaces, and their
presence in houses is considered a major
nuisance and health hazard in Cuba.
Molossus molossus has never been recorded from the United States, although its
broad distribution and good colonizing abilith!::s suggests its presence in southern Florida or southern Texas would not be extraordinary. Established colonies of bats of any
species have never been recorded in the
Florida Keys, although anecdotal records
JOllmal of MU1IImuiogy, 78(1): [03-105, 1997
suggest their presence (Lazell and Koopman, 1985). This paper reports on the first
occurrence of colonies of M. m. tropidorhynchus in the United States and the first
welI-documented occurrence of established
colonies of bats in the Florida Keys.
MATERIALS AND METHODS
The Florida Keys are a string of small islands
extending 200 km into the Straits of Florida off
the southern tip of Florida. The Keys occur at
24°N latitude and have a subtropical climate.
The major habitats on the Keys are West Indian
hardwood hammock, slash-pine rocklands, saltmarshes, and mangrove forests. The Keys have
a long history of occupation by humans; many
islands have suffered extensive loss of habitat
due to residential and commercial development.
The mammalion fauna of the Keys is depauperate compared to mainland Florida, consisting
primarily of relatively recent invasions from
Florida's mainland (Layne, 1974).
Colonies of bats were located as a result of
complaints by building occupants to the Florida
Game and Fresh Water Fish Commission Florida
Keys Field Office located in Marathon. Florida.
All calls were investigated and confirmed. Once
a colony was located, the number of bats in each
colony was estimated using evening flight
counts, Two observers counted bats leaving the
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104
JOURNAL OF MAMMALOGY
colony from around dusk to well after dark,
when bats could no longer be seen leaving the
colony. The two estimates were averaged as an
estimated count for the colony.
Voucher specimens were collected from each
colony site and sent to the American Museum
of Natural History for identification (AMNH
269529-269532). Bats were collected with mist
nets set near the roost entrance. Fresh specimens
were not collected from the Stock Island site,
but a mummified individual was obtained.
RESULTS
Three active colonies of bats were found
in the Florida Keys; one colony in Marathon (Vaca Key), one colony from Boca
Chiea Key, and one colony on Stock Island.
All three colonies were located in multistory buildings with flat roofs. The bats
were roosting in the space between the roof
and the ceiling of the top floor; entry into
the roof was through small gaps in the
structure. The common aspect of the three
colony sites was that access by humans to
the roosting colony was not possible.
Evening counts of bats exiting were conducted at the colony in Marathon on 2 February 1994; 100 bats were estimated to be
present. A second count at the colony in
Marathon on 8 September 1995 estimated
70 bats present. The colony on Boca Chica
was observed on 7 September 1994; 268
bats were counted leaving the building. The
colony on Stock Island was observed on 14
February 1994, but because of the location
of the roost in dense vegetation, an accurate
estimate of the number of bats was not
made. The occupant of the dwelling had
been living with the bats for several years
and suggested that there was a large number
of bats present.
DISCUSSION
Bats are scarce in the Florida Keys compared to mainland Florida, perhaps due to
the frequent severe hurricanes in the region,
a lack of suitable roosting habitats, inadequate sources of freshwater to drink, recent
geologic history, inhospitable habitats, and
extensive encroachment by humans (Jen-
Vol. 78, No.1
nings, 1958; Layne, 1974; Schwartz, 1952).
Although numerous records of bats on the
Keys have accumulated over the years, including records of Pipistrellus subfiavus,
Tadarida brasiliensis, Myatis austroriparius, Nycticeius humeralis, and Artibeus jamaciensis (Layne, 1974; Lazell, 1989; specimens in the collection of the Florida Museum of Natural History), these records are
often either poorly documented or largely
anecdotal.
The documentation of colonies of M. m.
tropidarhynchus clearly establishes that this
species occurs on the Florida Keys. The
presence of three widely-spaced colonies
(Marathon to Stock Island = 80 km) suggests that this species is well established on
the Keys. In November 1995, a specimen
of M. m. tropidorhynchus was collected in
Key West. I also obtained a photograph
taken on Upper Sugarloaf Key in 1988 of
a free-tailed bat that is most likely M. m.
tropidorhynchus. These records, plus several other credible reports of small bats observed at various locations throughout the
Lower Keys, suggest that additional colonies remain to be discovered.
The origin of colonies of M. m. tropidorhynchus in the Florida Keys is likely
Cuban, as this subspecies was previously
known only from Cuba where it is widespread and common. The means by which
they arrived on the Keys from Cuba,is open
to speculation. The extensive range of M.
molossus throughout Mexico, Central
America, and the Antillean islands illustrates that this species has excellent colonizing ability and capacity for over water
dispersal. The distance between Cuba and
Key West (ea. 100 km) suggests that M. m.
tropidorhynchus may have colonized the
Keys through a natural dispersal process
overwater through the Straits of Florida.
An alternative explanation for the colonization of the Keys by M. m. tropidorhyn_
chus also is plausible. Bats were both unintentionally (through centuries of boat traffic) and intentionally introduced on the
Keys by humans. In ] 929, R. C. Perky con_
February 1997
FRANK-MOLOSSUS IN THE UNITED STATES
structed a large bat tower on Lower Sugarloaf Key for mosquito control (Layne,
i974). Lower Sugarloaf Key lies about
midway between Vaca Key and Key West.
The bats used to populate the tower reportedly were collected from Cuba. and it is a
reasonable assumption that the widespread
and abundant M. m. tropidorhynchus would
have been an obvious choice for such a relocation effort. The Perky bat tower never
supported a colony of bats as intended. but
it is possible that the colonies of M. m. tropidorhynchus now resident in the Keys
originated from the 1929 introduction onto
Lower Sugarloaf Key.
ACKNOWLEDGMENTS
M. Miller of the Monroe County Extension
Service deserves credit for directing reports
about bats to my office. I thank J. Lazell and 1.
Layne for providing insight into bats residing on
the Keys. K. Koopman generously identified
specimens and commented on an earlier draft of
the manuscript. S. Chapell and R. Garcia provided valuable assistance counting bats and collecting specimens. I thank E. Forys and an anon-
105
ymous reviewer for reading an earlier draft of
this manuscript.
LITERATURE CITED
EISENBERG, J. E 1989. Mammals of the Neotropics:
the northern Neotropics: Panama, Colombia, Venezuela, Guyana, Suriname, French Guinea. The University of Chicago Press, Chicago, 1:1-449.
HALL, E. R. 1981. The mammals of North America.
Second ed. John Wiley ampers and Sons, New York,
l:1-600 + 90.
JENNINGS, W. L. 1958. The ecological distribution of
bats in Florida. Ph.D. dissertation, The University of
Florida, Gainesville, 125 pp.
LAYNE, J. N. 1974. The land mammals of South Florida. Pp. 386-413, in Environments of South Florida:
present and past (P. 1. Gleason, ed.). Miami Geological Society Memoir, 2:1-452.
LAZELL, J. D. 1989. Wildlife of the Florida Keys: a
natural history. Island Press, Washington, D. C, 250
pp.
LAZELL, J. D., AND K. E KOOPMAN. 1985. Notes on
bats of Florida's Lower Keys. Florida Scientist, 48:
37-41.
SCHWARTZ, A. 1952. The land mammals of southern
Florida and the Upper Keys. Ph.D. dissertation, The
University of Michigan, Ann Arbor, 180 pp.
SILVA TABOADA, G. 1979. Los murcielagos de Cuba.
Editorial Academy, Havana, Cuba, 421 pp.
Submitted 18 December 1995. Accepted 24 May 1996.
Associate Editor was Jane! K. Braun.