Caribbean Journal of Science, Vol. 38, No. 3-4, 281?284
Copyright 2002 College of Arts and Sciences
University of Puerto Rico, Mayagu?ez
A New Southern Distributional Limit
for the Central American Rodent
Peromyscus stirtoni
NEAL WOODMAN1, ELISA SCHNEIDER2, PAUL GRANT3,
DERRICK SAME4, KAREN E. SCHMALL5, AND JOHN T.
CURTIS6 1USGS/ Patuxent Wildlife Research Center,
Smithsonian Institution, PO Box 37012 National Mu-
seum of Natural History, NHB 378, MRC-111 Wash-
ington, DC 20013-7012, USA, 2c/o Peace Corps, P.O. Box
208, Lilongwe, Malawi 34901 Cherry Tree Bend, Victoria,
BC V8Y 1S1, Canada, 41116 North Point Drive,
Stevens Point, WI 54481, USA, 53144 Cowley Way #3,
San Diego, CA 92117, USA, 66010 N. Calle de la Culebra,
Tucson, AZ 85718, USA
Stirton?s deer mouse, Peromyscus stirtoni Dickey,
1928, is a Central American endemic species with a
discontinuous distribution in dry and seasonally dry
lowland habitats ranging from southeastern Guate-
mala to western Nicaragua (Jones, 1990; Reid, 1997). In
Nicaragua, P. stirtoni was known from seven speci-
mens at three localities in the west-central portion of
the country (Jones and Yates, 1983; Jones, 1990). Its
southernmost record was from Los Cocos, Boaco De-
partment. Our field work during 1998 and 2000 on Isla
de Ometepe in Lake Nicaragua (= Lago Colcibolca), at
least 80 km south of Los Cocos, yielded new,
vouchered records of P. stirtoni that extend its south-
ern distribution. Collecting in 2000 and 2001 by a sepa-
rate group from the Royal Ontario Museum (ROM)
yielded additional specimens from the same locality.
Specimens were identified by comparison with iden-
tified museum specimens and by using characters and
measurements outlined by Dickey (1928), Huckaby
(1980), Jones and Yates (1983), and Jones (1990).
Mice of the genus Peromyscus inhabit a number of
nearshore oceanic and lacustrine islands (e.g., Hall,
1981; Lomolino, 1993). Island populations typically are
subsets of mainland species with broad geographic
and habitat distributions. In contrast, the distribution
of Stirton?s deer mouse on the mainland is spotty,
probably resulting from an ability for long-distance
dispersal among scarce patches of favorable habitat,
the fragmentation of a much broader prehistoric dis-
NOTES 281
tribution, or a combination of vicariance and dis-
persal.
As in other areas, the distribution of P. stirtoni on
Isla de Ometepe is restricted. All captures were made
in Parque Natural ?Pe?a Inculta La Cabuya,? near
Santo Domingo, Rivas Department. La Cabuya is a ca.
1190-hectare reserve that extends from 50?150 m el-
evation. It lies on a flattened ridge of sharp-edged,
volcanic cobbles and boulders with little soil or leaf
litter. The rocky terrain probably kept the area from
being cleared for farming, as has happened in most
lowland areas on Isla de Ometepe. Old-growth, high-
canopied, evergreen dry tropical forest grows out of
this volcanic rubble, the trees supported by roots in-
tertwined amongst the rocks, reaching down to the
shallow water table. The forest in the study area is
dominated numerically by Hura crepitans (jabillo) and
Sterculia apetala (camajondura), with fewer Terminalia
oblonga (guayab?n), Ceiba pentandra (ceiba), Tabebuia
rosea (roble de sabana), Bursera simaruba (gumbo-
limbo), and Stemmadenia donnell-smithii (huevos de ca-
ballo). The understory contains many Urera baccifera
(chichicaste) and Luehea candida (gu?cimo). Despite se-
lective cutting of some trees (e.g., Cedrela odorata [ce-
dro], for canoes), the forest appears mostly undis-
turbed. This impression was reinforced by the relative
abundance of emballonurid and phyllostomid bats in
La Cabuya (29 individuals of at least 7 species in a
single net during 10 hours in 1998) and the lack of the
common vampire bat, Desmodus rotundus, a species
abundant (17% of captures in 1998) elsewhere on Isla
de Ometepe before eradication efforts in early 2000.
We trapped for small mammals at five other sites on
Isla de Ometepe within the ca. 30?975 m elevational
range of P. stirtoni. Previous expeditions there in 1964
and 1968 sampled at least seven other localities (J. R.
Choate, H. H. Genoways, T. E. Lawlor, J. D. Smith?
unpublished field notes and catalogs, University of
Kansas Natural History Museum [KU]). Although Lio-
mys salvini (Salvin?s spiny pocket mouse) and Sigmo-
don hispidus (hispid cotton rat) were present in dis-
turbed rocky areas elsewhere on the island, the
relatively undisturbed forest at La Cabuya was the
only site where P. stirtoni was taken. Other workers
have reported capturing P. stirtoni in disturbed habi-
tats elsewhere in Central America (e.g., Peppers et al.,
1999).
Peromyscus stirtoni appeared to be locally abundant
TABLE 1. Descriptive statistics for adult Peromyscus stirtoni from Isla de Ometepe and mainland Nicaragua.
Statistics presented are mean ? SD and range. All measurements in millimeters, weight in grams. Cranial
measurements are defined and illustrated by Musser et al. (1998).
Isla de Ometepe Mainland
external measurements
(n = 7) (n = 6)
length of head and body (HB) 102 ? 7 103 ? 5
(94?111) (97?109)
length of tail (LT) 87 ? 7 96 ? 7
(75?95) (86?107)
relative tail length (LT/HB ? 100) 85 ? 4% 93 ? 10%
(79?90) (79?107)
length of hind foot (LF) 23 ? 0.5 23 ? 1
(23?24) (22?24)
weight
(n = 7) (n = 4)
29 ? 4 31 ? 3
(23?35) (28?35)
cranial measurements
(n = 7) (n = 7)
occipitonasal length (ONL) 30.0 ? 1.5 29.5 ? 0.6
(28.0?31.8) (28.6?30.2)
greatest zygomatic breadth (ZB) 14.1 ? 0.6 13.8 ? 0.4
(13.2?14.6) (13.0?14.1)
interorbital breadth (IB) 5.0 ? 0.1 4.9 ? 0.1
(4.8?5.2) (4.7?5.1)
breadth of zygomatic plate (BZP) 2.3 ? 0.2 2.4 ? 0.2
(2.0?2.5) (2.2?2.6)
crown length of maxillary toothrow
(CLM1?3) 4.2 ? 0.1 3.9 ? 0.1
(4.0?4.4) (3.7?4.1)
length of incisive foramina (LIF) 5.5 ? 0.4 5.8 ? 0.3
(5.3?6.4) (5.4?6.2)
NOTES282
in 1998, but less abundant in subsequent years. We
captured 10 P. stirtoni and 5 Liomys salvini using 30
Sherman traps at La Cabuya on the nights of 9 June
and 11 June 1998 (60 total trapnights). We kept two
adult males, two adult females, and one subadult fe-
male P. stirtoni as vouchers. On the night of 15 June
2000, we captured one adult male P. stirtoni in 30 Sher-
man traps set at La Cabuya. Specimens from La
Cabuya in the ROM include two adult females, one
juvenile female, and one juvenile male from 17 Febru-
ary 2000, and an adult female from 23 February 2001.
Reproductive data from the individuals captured on
Isla de Ometepe are informative but represent only
two short portions of the year. None of the females
was gravid but three captured from 17?23 February
were lactating, and one of the two females captured on
12 June had enlarged teats suggestive of recent lacta-
tion. This last individual had an extensive nematode
infestation of the mouth, pharynx, and esophagus. The
adult males from June had abdominal testes, measur-
ing 5 ? 3, 5 ? 3, and 12 ? 6 mm. Individuals in paler
gray juvenile pelage were captured on 17 February
and 10 June.
Initial comparisons of selected cranial variables
from specimens we collected in 1998 suggested that
individuals from La Cabuya might be larger than
those on the mainland, possibly corresponding to the
?island rule? of biogeography (Lomolino, 1985). To
test this possibility, we used Minitab Release 8 to carry
out principal components analysis (PCA) of a correla-
tion matrix of six log-transformed cranial variables
(Table 1; Musser et al., 1998) from seven adult P. stir-
toni from Isla de Ometepe and seven adults from the
mainland. These samples represent the total number
of adults (as determined by complete adult pelage and
FIG. 1. Plot of scores on PC I and PC II from PCA of adult Peromyscus stirtoni from Isla de Ometepe and
mainland Nicaragua.
TABLE 2. Factor loadings for PC I and PC II from
PCA of six cranial variables from samples of P. stirtoni
from Isla de Ometepe and mainland Nicaragua. Vari-
ables are listed in descending order by their loadings
on PC I. Abbreviations of measurements are explained
in Table 1.
Variable
Loadings
PC I PC II
ONL ?0.568 0.089
ZB ?0.504 0.248
IB ?0.061 0.667
BZP ?0.466 ?0.301
CLM1?3 ?0.204 0.464
LIF ?0.401 ?0.424
eigenvalue: 2.7113 1.7699
proportion of
variation explained: 45.2% 29.5%
NOTES 283
fully erupted, worn dentition) currently available
from Nicaragua. The resulting plot of specimens on
PC I and PC II (Fig. 1) indicates modest separation
between the two samples along PC II. This distribu-
tion in part reflects the tendency of the island sample
to have a broader zygomatic plate, longer maxillary
toothrow, and shorter incisive foramen (Table 2). Al-
though these results provide a tantalizing suggestion
of morphological divergence, the low sample sizes
preclude drawing firm conclusions about the distinc-
tiveness of the two groups. There is little difference in
overall size as measured by PCA (PC I in Fig. 1), head-
and-body length (Table 1), weight, or cranial variables
(e.g., for ONL, Mann-Whitney U = 33; n1 = n2 = 7; P >
0.10). In fact, the overall size variation exhibited by the
sample from La Cabuya is greater than that exhibited
by the mainland sample, which includes mice from
three departments of Nicaragua (Fig. 1). The longer
relative tail length (Table 2) of the mainland mice is
not statistically significant (Mann-Whitney U = 32.5;
n1 = 7, n2 = 6; P > 0.05).
Subfossil remains of Stirton?s deer mouse reported
from cave sediments further south in Guanacaste
Province, Costa Rica (Woodman, 1988), were dated
recently at 2855 ? 50 yrs B.P. (NSF-Arizona AMS
Laboratory sample number AA35317). These remains
were recovered from a region that still lacks a com-
plete survey of its modern mammalian fauna, and it is
possible that P. stirtoni still occurs there. The above
records emphasize the incompleteness of our knowl-
edge of the distribution and status of many small
mammals in Nicaragua (and throughout much of Cen-
tral America) and the continued need for basic bio-
logical surveys and for samples adequate to character-
ize populations of poorly known species.
Acknowledgments.? Permits for field work on Isla de
Ometepe were kindly granted by MARENA. Logisti-
cal support was provided by the Isla de Ometepe Bio-
logical Field Station. Teresa Snyder-Leiby identified
the plants. Robert P. Anderson, Maria Eifler, Thor Hol-
mes, and Burton K. Lim provided valuable assistance
with field notes at their respective institutions. We thank
the curators and collection managers at KU and ROM
for loans and/or permission to study specimens under
their care. Robert P. Anderson, Robert M. Timm, and an
anonymous reviewer provided substantive comments
that greatly improved on previous drafts of this paper.
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APPENDIX 1: SPECIMENS EXAMINED
Peromyscus stirtoni (18).?NICARAGUA: BOACO:
Los Cocos, 220 m, 14 km S Boaco (KU 115570?115572).
MANAGUA: 8 km (by road) N Las Maderas, 380 m (KU
106797, 106798). MATAGALPA: 11 mi SE Dario (KU
71541, 71542). RIVAS: Parque Natural ?Pe?a Inculta de
La Cabuya,? 50 m, 1 km NNW Santo Domingo, Isla de
Ometepe (KU 157735?157739,158892; ROM 112210?
112213, 112731).
NOTES284