The Persistence of Endangered Florida Salt Marsh Voles in Salt Marshes of the Central Florida Gulf Coast
Althea S. Hotaling, H. Franklin Percival, Wiley M. Kitchens, and John W. Kasbohm
Southeastern Naturalist, Volume 9, Issue 4 (2010): 795–802
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2010 SOUTHEASTERN NATURALIST 9(4):795–802
The Persistence of Endangered Florida Salt Marsh Voles in
Salt Marshes of the Central Florida Gulf Coast
Althea S. Hotaling1,*, H. Franklin Percival1, Wiley M. Kitchens1,
and John W. Kasbohm2
Abstract - Two endangered Microtus pennsylvanicus dukecampbelli (Florida
Salt Marsh Vole) were captured at a new location, in February of 2009, at Lower
Suwannee National Wildlife Refuge. Since the species discovery in 1979, only 43
Florida Salt Marsh Voles (hereafter FSM Vole) have been captured. Outside of the
type locality, this is only the second documented location for the FSM Vole. Given
the difficulty in trapping this species and the lack of information about its life
history, its discovery in a new location lends itself to the possibility that it is more
widespread in the Central Florida Gulf Coast than previously thought. Although
much of the salt marsh in the area is in public ownership, a good deal of it has already
been altered by logging or development and is threatened by global climate
change. More research is needed to adequately protect and manage the habitat for
the FSM Vole. A study of FSM Vole coastal salt marsh habitat could also serve as
a valuable monitoring tool for subtle changes in salt marsh habitats as global climate
The endangered (US Fish and Wildlife Service 1991) Microtus pennsylvanicus
dukecampbelli Woods, Post, and Kilpatrick (Florida Salt
Marsh Vole; hereafter FSM Vole) remains virtually unstudied in its salt
marsh habitat. The first FSM Voles were captured in 1979. Chromosomal
and electrophoretic data collected by Woods et al. (1982) verified that the
FSM Vole was a new subspecies of Microtus pennsylvanicus Ord (Meadow
Vole). Local area fossils also revealed that the FSM Vole is a relict of
a previously widespread population of Microtus that occurred throughout
the Gulf Coastal Plain during the lower sea levels of the Pleistocene
(Woods et al. 1982). The FSM Vole’s range has been restricted to its
current range by changing sea level and potentially could continue to be
constricted in response to rising sea level and associated changes in habitat
(Woods et al. 1982). Improved understanding of habitat associations
and management techniques is necessary to assess the potential impacts
of changing climate conditions.
The FSM Vole is a small (≈186.1 mm), short-tailed (≈48.8 mm) rodent,
with a blunt head and small inconspicuous ears. Its fur is dark
1USGS Florida Cooperative Fish and Wildlife Research Unit, University of Florida,
Box 110485, Building 810, Gainesville, fl32511. 2Refuge Manager, Lower Suwannee
and Cedar Keys National Wildlife Refuge, 16450 NW 31st Place, Chiefland, fl32626. *Corresponding author - email@example.com.
796 Southeastern Naturalist Vol. 9, No. 4
brown dorsally and dark gray ventrally (Woods 1992). The Florida subspecies
differs from the common Meadow Vole in its larger size, darker
coloration, relatively smaller ears, and specific skull characteristics
(Woods 1992). The life history of the FSM Vole has not been well studied,
but its population, like other Microtus populations, is likely cyclical,
which may explain some of the difficultly in trapping (Woods 1992).
Many researchers have found that Microtus population sizes can fluctuate
dramatically, with the timing and duration of the fluctuations varying
widely among species and even among populations of the same species
(Getz and McGuire 2009, Krebs 1996, Krebs and Myers 1974, Krebs et
al. 1969, Saitoh et al. 1998, Taitt and Krebs 1985). Therefore, it is possible
that some trapping efforts occurred during times when FSM Vole
population numbers were naturally low and others when it was high, explaining
the variability of success in capturing the FSM Voles. A total of
18 different sites have been trapped for the FSM Vole (Fig. 1), with varying
amounts of effort (Table 1). This study was performed with limited
resources and is not meant to quantify the population status of the FSM
Vole but to document that it still persists in the Gulf Coast salt marshes
around Cedar Key even after the devastating hurricane season of 2005.
Additionally, much data has been lost about the specifics of previous trapping
efforts, like habitat type trapped, distance between traps, and number
of nights each site was trapped.
Three other small mammals (Sigmodon hispidus Say and Ord [Hispid
Cotton Rat], Oryzomys palustris Harlan [Marsh Rice Rat], and Peromyscus
gossypinus LeConte [Cotton Mouse]) typically occupy salt marshes
and nearby uplands of the Gulf Coast with the FSM Vole (Woods et al.
Table 1. The number of sites, trap nights, total nights of trapping, and Florida Salt Marsh Voles
(FSM Voles) captured, as well as the year and principal researcher during 9 trapping episodes
from 1979–2000. U = unknown data. There is no known documentation of the effort involved
in Woods’ second trapping effort that resulted in the capture of 22 FSM Voles. (Bentzien 1989;
Doonan and Morgan 2002; R. McNab, University of Florida, Gainesville, fl, unpubl. data;
Smith 1990; USFWS 2004; Woods et al. 1982).
Total nights # of
Year Researcher # of sites Trap nights of trapping FSM Voles
1979–81 C. Woods 1 1782 6 9
U U 22
1988 L. Smith/C. Woods 1 1025 13 1
1989 M. Bentzien 4 509 4 0
1993–94 R. McNab 11 1000 11 0
1996 T. Doonan 7 2352 27 5
2004 S. Barlow 4 600 13 3
2005 S. Barlow 1 180 3 1
2006 F. Percival 4 1000 10 0
2009 A. Hotaling 9 2675 28 2
Totals 42 11,123 115 43
2010 A,S. Hotaling, H.F. Percival, W.M. Kitchens, and J.W. Kasbohm 797
Figure 1. This map shows the locations of the nine sites trapped in this study (+, ); the
bold plus signs () were also trapped in 2004 by Steve Barlow and Lower Suwannee and
Cedar Keys National Wildlife Refuge (LSNWR) staff. The type locality is indicated on
the map with a star (). The 4 sites from Crystal River to Cedar Key marked by (*) were
trapped by Benzien in 1989 without any successful Florida Salt Marsh Vole (FSM Vole)
captures. Additional sites at LSNWR that were trapped in 2006 are marked with a (■).
The inset map indicates the only locations (▲) where FSM Voles have been caught. The
left-most symbol is on Long Cabbage Key, where the FSM Voles were caught during this
study, the middle triangle marks the spot where FSM Voles were caught by Steve Barlow
in 2004 and 2005, and the right triangle marks the vole captures from 1979, 1980, 1981,
1988, and 1996 at the type locality.
798 Southeastern Naturalist Vol. 9, No. 4
1982). Distichlis spicata L. (Saltgrass)-dominated habitat appears to be
preferred by FSM Voles, as nearly all FSM Voles that have been captured
were found in Saltgrass-dominated habitat that occurs at a slightly higher
elevation than Spartina alterniflora Loisel (Saltmarsh Cordgrass) and Juncus
roemerianus Scheele (Needlegrass Rush) in the marsh (Woods 1992,
Woods et al. 1982). Fisler (1961) also found that Microtus californicus
Peale (California Salt Marsh Vole) was most commonly found in habitat
dominated by Salicornia ambigua Michx. (Chickenclaws) and Saltgrass.
Saltgrass is a unique salt marsh plant that has a variety of adaptations that
make it tolerant of hypersaline conditions (Hansen et al. 1976). It is not
known if FSM Voles are found most often in this habitat type because of
competitive pressure or preference. The objective of this study was to determine
if there were still FSM Vole populations in the refuge and, if so,
where they were located.
This study was conducted at Lower Suwannee National Wildlife Refuge
(LSNWR) from 20 January to 6 March 2009. The 21,500-ha refuge is located
in Levy and Dixie counties on the Central Gulf Coast of Florida (Fig. 1). The
study focused on the approximately 6309 ha of salt marshes located on the
islands and shores of LSNWR. There were a total of 2800 trap nights in nine
sites, but 125 misfires, or occasions when a trap was closed with no small
mammal or open with evidence of a mammal, resulted in a total of 2675 trap
nights. Trapping occurred in 9 different sites, which varied in size and shape
but were chosen because they contained the largest extent of Saltgrassdominated
One transect was placed in each of the nine sites, 100 Sherman livetraps
baited with scratch grain were placed one every 10 m along 1-km-long
transects. Traps were left in each of the nine sites for 3 nights, resulting in a
total of 28 nights for all nine sites (including an extra night in the site where
the FSM Voles were captured). Diurnal trapping was not permitted due to
high midday temperatures in Florida, even in the winter months. Traps were
only left in a site for 3 days to increase the number of sites or area of LSNWR
that could be trapped.
Traps were opened at dusk and checked early in the morning. If a trap
misfired or contained a rodent, it was replaced with a clean trap to eliminate
the possibility that scats left by other species such as Hispid Cotton
Rat or Marsh Rice Rat precluded or reduced the number of FSM Voles
captured. Traps were cleaned using a bleach water mix and scrub brushes.
Bait and cotton were replaced in all traps every 3 days, when traps were
moved. Traps were attached to foam boards (40 cm x 15 cm x 2 cm) with
rubber bands, and a survey flag was inserted through the foam and into the
substrate, so that the traps could float during high water events. Species,
2010 A,S. Hotaling, H.F. Percival, W.M. Kitchens, and J.W. Kasbohm 799
sex, body length, tail length, hind-foot length, and mass were recorded for
each mammal caught. All animals were released at the point of capture immediately
During the study, 245 small mammals were captured, including
2 FSM Voles (Table 2). The FSM Voles were captured on Long Cabbage
Key, a small island just offshore of the 2004 vole capture site and
about 5 miles from the only other capture location, the site locality, in
Saltgrass-dominated habitat. The voles were both males, but one was a
sub-adult. The sub-adult weighed 29 grams, was 106 mm long, with a
tail length of 25 mm, and a hind foot or pes length of 18 mm. The adult
weighed 75 grams, was 162 mm long, with a 39-mm tail, and a 22-mm hind
foot or pes length. The juvenile was captured on 11 February 2009, and the
adult was captured on 12 February 2009.
The percent cover of each plant species and the dominant species or
species with the highest percent cover was noted for the 1.5-m2 area around
each trap. There were 1676 (60 %) traps placed in Saltgrass-dominated
habitat, 270 (10 %) in Juncus roemerianus-dominated habitat, 366 (13 %)
in Spartina alterniflora-dominated habitat, 300 (11 %) in unknown habitat
type, and 188 (6 %) that were in habitat dominated by other vegetation.
We then calculated the average number and species of small mammals
caught per 100 traps in each of the dominant habitat types (Table 2). The
number of small mammals caught was relativized in this manner to look at
habitat preferences. For instance, the highest number of small mammals,
118, was trapped in Saltgrass-dominated habitat, but trapping effort was
Table 2. The absolute number (n) of each small mammal species caught in each habitat type
(Distichlis spicata [Saltgrass]-dominated, Juncus roemerianus [Needlegrass Rush]-dominated,
Spartina alterniflora [Saltmarsh Cordgrass]-dominated) and the relativized number caught per
Oryzomys Sigmodon Peromyscus pennsylvanicus
Habitat type palustris hispidus gossypinus dukecampbelli Total
n 104 10 2 2 118
Per 100 traps 6.0 0.6 0.1 0.1
n 39 2 1 0 42
Per 100 traps 14.4 0.7 0.4 0.0
n 57 4 0 0 61
Per 100 traps 15.6 1.1 0.0 0.0
Other 21 3 0 0 24
Total 221 19 3 2 245
800 Southeastern Naturalist Vol. 9, No. 4
also greatest in Saltgrass-dominated habitat, with 60% of traps located
there. The relativized number show that Marsh Rice Rat clearly prefers
Needlegrass Rush- or Saltmarsh Cordgrass-dominated habitat even though
more of them were caught in Saltgrass habitat. This helps to give some idea
of the habitat niches of the different species within the salt marsh.
This study has shown that the FSM Vole still persists in the salt
marshes of the central Florida Gulf Coast. A good deal of trapping effort
was required to locate any FSM Voles, and little is known about total population
numbers and the extent of their range. More research is necessary
on this rare species and the potential effects that global climate change
may have on its survival. The Gulf Coastal Plain is shallow and lacks the
topography necessary to hold rising salt water back, which allows even
small increases in sea level to encroach inland considerable distances
(FFWCC 2008). There is much debate in the literature about whether salt
marsh communities along the Gulf Coast will be able to keep pace with
rising water, and some researchers predict that the area of salt marsh will
be greatly restricted or even lost all together (Harris and Cropper 1992).
Global climate change will also likely bring more frequent and severe
tropical depressions and hurricanes to the area, putting salt marshes
and their inhabitants at further risk (Intergovernmental Panel on Climate
Change 2007). It is likely that many small mammals perish during severe
storms. If tropical depressions and hurricanes become more frequent as
predicted, populations of small mammals may not have enough time to
recover before the next storm. This is of particular concern for rare and
endangered species that likely already exist at low and constantly fluctuating
population levels. To more effectively manage the FSM Vole, it will
be important to learn more about its life history, population dynamics, and
habitat requirements as well as how climate change might alter the salt
marsh and its inhabitants.
Funding was provided through the Quick Response Program of the US Geological
Survey. We would like to thank Scotland Talley, Melissa Tucker, and Billy Brooks
for their review of the manuscript and for providing information on past FSM Vole
trapping efforts, and field technician Amy Witt for her help with data collection. We
also appreciate the help of the staff of Lower Suwannee National Wildlife Refuge,
who hosted us and helped with field logistics.
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