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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 change progresses. Introduction 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 - theah@ufl.edu. 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. Methods 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 habitat. 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 following processing. Results 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 100 traps. Microtus Oryzomys Sigmodon Peromyscus pennsylvanicus Habitat type palustris hispidus gossypinus dukecampbelli Total D. spicata n 104 10 2 2 118 Per 100 traps 6.0 0.6 0.1 0.1 J. roemerianus n 39 2 1 0 42 Per 100 traps 14.4 0.7 0.4 0.0 S. alterniflora 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. Discussion 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. Acknowledgments 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. Literature Cited Bentzien, M.M. 1989. Florida Salt Marsh Vole survey. Unpublished Report. US Fish and Wildlife Service, Jacksonville, fl. 5 pp. 2010 A,S. Hotaling, H.F. Percival, W.M. Kitchens, and J.W. Kasbohm 801 Doonan, T.J., G.L. Morgan. 2002. Abundance and Distribution of the Florida Salt Marsh Vole (Microtus pennsylvanicus dukecampbellli) (Project 9314221 1000). Unpublished Final Project Report. Bureau of Wildlife Diversity Conservation, Florida Fish and Wildlife Conservation Commission. Olustee, fl. Fisler, G.F. 1961. Behavior of salt-marsh Microtus during winter high tides. Journal of Mammalogy 42(1):37–43. Florida Fish and Wildlife Conservation Commission (FFWCC). 2008. Wildlife 2060: What's at stake for Florida? Tallahassee, fl. 28 pp. Getz, L.L and B. McGuire. 2009. 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Biology of new world Microtus. Special Publication No. 9, American Society of Mammalogists, Provo, UT. US Fish and Wildlife Service (USFWS). 1991. Endangered and threatened wildlife and plants; endangered status for the Florida Salt Marsh Vole. Federal Register 56(9):1457–1459. USFWS. 2004. Three Florida Salt Marsh Voles—an extremely rare subspecies— discovered on Florida’s Lower Suwannee National Wildlife Refuge. USFWS News Release. Atlanta, GA. 802 Southeastern Naturalist Vol. 9, No. 4 Woods, C.A. 1992. Endangered: Florida Saltmarsh Vole (Microtus pennsylvanicus dukecampbelli). Pp. 131–139, In S.R. Humphrey (Ed.). Rare and Endangered Biota of Florida Vol. 1 Mammals. University Press of Florida. Gainesville, fl. 392 pp. Woods, C.A., W. Post, and C.W. Kilpatrick. 1982. Microtus pennsylvanicus (Rodentia: Muridae) in Florida: A Pleistocene relict in a coastal saltmarsh. Bulletin of the Florida State Museum Biological Sciences 28(2):25–52.