Showing papers in "Virginia journal of science in 2006"
TL;DR: In this study, it is learned that Virginia rice rats ate higher proportions of plant material than at other geographic locations, plus varying amounts of crabs, snails, and arthropods (mostly insects).
Abstract: The marsh rice rat, Oryzomys palustris, is the dominant semi-aquatic rodent living in tidal marshes of the Virginia coastal plain. Described as highly carnivorous, this species is known to consume a range of animal foods , including crustaceans, mollusks, fish, and arthropods, as well as some plant foods . Analysis of stomach contents from rice rats collected from Eastern Shore tidal marshes throughout an annual cycle revealed that all 103 stomachs contained di cots, 82 percent had monocots, 61 percent had crabs and insects, and 38 percent had snails. Thirty-eight percent of stomachs contained foods in all five categories, no stomach was empty or contained fish , and 84 percent of stomachs had amounts of hair, probably ingested during self-grooming. In sum, Virginia rice rats are carnivorous but consume greater amounts of plant foods compared to populations that have been studied in Georgia and Louisiana. INTRODUCTION The marsh rice rat, Oryzomys palustris, is a semi-aquatic rodent with its highest abundances in wet fields and marshes, mostly of the southeastern US (Wolfe 1982). Distributed along the eastern seaboard southward from coastal Pennsylvania to the tip of Florida and westward to Corpus Christi, Texas, its range extends northward along the Mississippi River basin into southern Missouri and Illinois. In Virginia, it is common in tidal marshes of the coast and Chesapeake Bay and is present in some grassland habitats as far west as the fall line (ca.Interstate Highway 95; Linzey 1998). The marsh rice rat readily takes to water to forage and escape from predators, and can be caught in floating live traps (personal observation, RKR). Its swimming ability has been studied by Esher et al. (1978) in Mississippi and Carter and Merritt (1981) in Virginia, and inter-island movements of marked rice rats have been documented for the Virginia barrier islands (Forys and Dueser 1993). Medium in size among rodents (up to 80 g), Oryzomys is considered to be highly carnivorous, second to North America's most carnivorous rodent, the grasshopper mouse, Onychomys, a desert grassland mouse of the western states. The meat-eating proclivities of marsh rice rats were observed by Schantz (1943), who reported them eating the bodies of trapped muskrats, a behavior also observed by RKR (unpublished) on trapped small mammals on Fisherman Island, Virginia. The natural history of the marsh rice rat is summarized in Wolfe (1982). 1 Corresponding author: Robert K. Rose, Department ofBiological Sciences, Old Dominion University, Norfolk, Virginia, Phone: 757-683-4202, Email: brose@odu.edu 116 VIRGINIA JOURNAL OF SCIENCE The objectives of our year-long study were to learn the kinds and proportions of foods eaten by marsh rice rats taken from tidal marshes of the Eastern Shore of Virginia and their seasonality of food selection. Oryzomys palustris is codominant in these tidal marshes with the meadow vole, Microtus pennsylvanicus (March 1995 Bloch and Rose 2005), with the latter being almost exclusively herbivorou~ (Zimmerman 1965, among others). Where the diet of marsh rice rats has been examined in Louisiana (Negus et al., 1961), Florida (Pournelle, 1950) and Georgia (Sharp, 1967), Oryzomys consumes both plant and animal materials, in differing proportions. In our study, we learned that Virginia rice rats ate higher proportions of plant material than at other geographic locations, plus varying amounts of crabs, snails, and arthropods (mostly insects). MATERIALS AND METHODS The $tudy1\\rea This study was conducted over a one-year period, from May 1994-April 1995. The research goal was to collect samples of up to 15 animals each month from two seaside sites in Northampton County, Virginia, one located ca. 300 m south of Oyster and the other 500 m east of Townsend. In October, an opportunity was presented to examine animals from the marshes of nearby barrier islands (Myrtle, Ship Shoal, Smith, and Mockhorn), so the sample size for that month was much larger than the others. For unknown reasons, rice rats were scarce during the summer months of June-August, and only two animals were collected during that time (Table 1 ), despite an increased trapping effort then compared to other months. March (1995), in earl ier studies of the population dynamics of rice rats in similar tidal marshes on the Eastern Shore, had also found density to be low or near zero in June and July, and Negus et al. (1961) caught 13 rice rats in July in 2145 trap-nights and 3 in June of another year in 504 trap-nights, both < 1 rice rat per 200 trap-nights, indicating behavioral or other changes lowering their trappability in summer. Both study sites were in tidal marshes backed by areas of dense common reed, Phragmites australis. The flora of the marshes included Spartina alterniflora (salt grass), S. patens (salt meadow hay), Panicum sp. (panic grasses), Juncus roemeranius (black needle-rush), Salicornia sp. (glasswort), Baccharis halimifolia (saltbush), and Typha latifolia (cattail). Both marshes are flooded twice daily in the area of the Juncus, whereas the S. patens areas are flooded only during monthly high or wind tides. The border between Baccharis shrubs and Juncus often supported a more substantial wrack line than that between S. patens and Juncus. This wrack line provided additional structure to a marsh with relatively little structure, except for the Baccharis shrubs. Trapping cand m.aboratory[Procedures Transects of Fitch live traps (Rose 1994) were placed 2-3 m apart along the borders, i.e., at the normal extent of the daily high tide. Baited with wild birdseed and tended early each morning, these traps yielded mainly marsh rice rats and meadow voles, with lesser numbers white-footed mice (Peromyscus leucopus) and house mice (Mus musculus), and even fewer least shrews (Cryptotis parva) and short-tailed shrews (Blarina brevicauda). Only marsh rice rats were collected for this study. Marsh rice rats were returned to the laboratory, euthanized by chloroform anesthesia, and frozen. FOODS OF RICE RATS IN TIDAL MARSHES 117 TABLE I. For each sex, sample sizes of the age categories of rice rats, following the criteria of Negus et al. (1961 ). Age category I = juvenile, 2 = subadult, 3 = near adult, and 4 = adult. The months have been grouped into seasons, with June-September SUmmer, October and November AUtumn, December-February Winter, and March-May SPring. MONTH TOTAL # # FEMALES # MALES AGEi AGE2 AGE3 AGE4 May SP 6 I 5 2 0 0 4 June SU I I 0 I 0 0 0 July SU 0 0 0 0 0 0 0 August SU I I 0 I 0 0 0 September SU 7 1 6 2 2 I 2 October AU 36 10 26 8 8 3 17 November AU 3 2 I 3 0 0 0 December WI 9 4 5 5 I 3 0 January WI 15 6 9 12 0 2 February WI 12 7 5 7 2 2 March SP 9 2 7 I 0 4 4 April SP 4 0 4 0 I 0 3 Totals 103 34 69 41 14 15 33 In order to compare what was eaten with what foods were available, samples of all potential food sources in the tidal marshes were collected from the same marshes as the rice rats, returned to the lab, processed, and made into reference slides. After samples of plant and animal materials had been pulverized in a Waring® blender to a consistency comparable to that of stomach contents ofrice rats, the material then was washed in water, air-dried, and placed on microscope slides with Kleermount, a mounting medium, and covered with standard coverslips. Reference slides were made of three dicots (Baccharis, Salicornia, and Typha), four monocots (Juncus, Panicum sp., Spartina alternifolia, and S. patens), and four animals: fiddler crab, Uca minax; periwinkle, a univalve snail, Littorina irrorata; mummichog, a small brackish-water fish, Fundulus heteroclitus; and several arthropods, including grasshoppers, crickets, flies, and spiders, hereafter called 'insects'. After the rice rats were thawed, standard measurements were taken (total length, lengths of tail, foot and ear, body mass) and the reproductive information was recorded for a related research project (Dreelin 1997). The contents of each stomach were removed, washed in water, air-dried, and then placed in separate l 0-ml beakers, covered, labeled, and placed in the freezer to avoid contamination. For analysis, two samples from each stomach were placed on two slides with Kleermount, covered with standard coverslips, and compared to reference slides (method modified from Fleharty and Olson 1969). The contents were analyzed using a percent volume method, in which the amount of each type of food was visually estimated using a standard 10 X IO ocular grid (Whitaker and French 1984). Food items were identified as belonging to one of six categories: dicotylenous plant, monocotyledonous plant, crab, snail, fish, and arthropod. In each of the l O randomly selected 10 X l O ocular fields, the volume of each food type was estimated and recorded. The volumes from both slides of each stomach were then summed, and an average was calculated to determine the percent volume of each food type for each stomach. 118 VIRGINIA JOURNAL OF SCIENCE TABLE 2. Mean percent volumes and standard errors (in parentheses) based on examination of JO microscopic fields in each of two slides per marsh rice rat, using the technique of Whitaker and French ( 1984). Values are given for each month of study and for each food category. MONTH DICOT MONOCOT CRAB SNAIL INSECT May 77.2 (0.11) 8.1 (0.07) 7.1 (0.08) 3.7 (0.07) 4.0 (0.07) June 95.8 (----) 4.2 (----) 0.0(----) 0.0 (----) 0.0 (----) July --(----) --(----) --(----) --(----) --(----) August 73.4 (----) 10.9 (----) 4.2 (----) 0.0 (----) 11.5 (----) September 79 .5 (0.05) 9.2 (0.02) 6.1 (0.06) 2.9 (0.04) 2.1 (0.03) October 66.1 (0.04) 12.0 (0.04) 6.8 (0.03) 3.9 (0.03) 11 .3 (0.04) November 76.8 (0.08) 4.9 (0.05) I 1.6 (0.1 1) 3.6 (0.07) 3.2 (0.05 ) December 85.4 (0.08) 6.8 (0 .06) 4.6 (0.06) 1.7 (0.02) I .5 (0.03) January 75.8 (0.05) I 0.5 (0.04) 6.6 (0.04) 6.0 (0.04) I. I (0.01 ) February 75 .7 (0.06) 16.9 (0.05) 3.7 (0.03) 2.3 (0.03) 1.4 (0.02) March 62 .3 (0.07) 30.1 (0.05) 0.2
5 citations
TL;DR: Gaines et al. as discussed by the authors found that southern bog lemmings were present on 38 of 165 (23%) pitfall-trapping sites; their frequency was much greater in prime habitats dominated by grasses and sedges on damp organic soils.
Abstract: The Dismal Swamp subspecies of the southern bog lemming, Synaptomys cooperi helaletes, was named based on specimens collected during the 18951898 biological surveys conducted in the Dismal Swamp by the US Department of Agriculture. Unknown in the 20 th Century until re-discovered in 1980, this small boreal rodent was believed to be restricted to the Great Dismal Swamp ofV irginia and North Carolina where the cool damp conditions had permitted it to survive during the Holocene. However, field studies conducted since 1980 have revealed southern bog lemmings to be widespread throughout southeastern Virginia, with populations encompassing an area of more than 3300 km 2, including the cities of Virginia Beach, Chesapeake, and Suffolk, and Isle of Wight County. Lemmings were present on 38 of 165 (23%) pitfall-trapping sites; their frequency was much greater in prime habitats dominated by grasses and sedges on damp organic soils. Thus, southern bog lemmings are distributed widely in southeastern Virginia and, where present, they often are among the most numerous species of small mammal. INTRODUCTION The southern bog lemming, Synaptomys cooperi, distributed from Kansas and Nebraska northward through Minnesota and Manitoba, eastward through Canada, and southward into the Appalachian Mountains of North Carolina and Tennessee (Hall 1981 ), is one of the most enigmatic small mammals in North America. In some Midwestern states, highly trappable and high-density populations coexist with prairie voles in me sic or xeric grassland habitats (Kansas: Gaines et al. 1977; Illinois: Beasley and Getz 1986; Indiana: Krebs et al. 1969). In other permanently wet sites where herbivorous potential competitors often are absent, however, southern bog lemmings are difficult to trap. For example, isolated relic populations associated with permanently flowing springs (now incorporated into state-run fish hatcheries) are known from Meade County in southwestern Kansas and Dundy County in southwestern Nebraska. Other relic populations are believed to be restricted to the Pine Barrens of southern New Jersey and to the Dismal Swamp of southeastern Virginia and adjacent North Carolina. Thus, populations of this small stocky rodent with short tail and. tiny ears are highly patchy in both space and time. For example, in Douglas County in eastern Kansas, where generations of mammalogists have been trained at the University of Kansas since the 1920s, grassland populations existed for about four years starting in the middle 1920s (Lindale 1927, Burt 1928), then disappeared, reappeared in the middle 1940s, disappeared, and then reappeared in the mid-l 960s, since when they have persisted (Rose et al. 1977, Norman A. Slade, University of Kansas, pers. comm., October 2005). Understanding its ·spatial distribution is made difficult because 154 VIRGINIA JOURNAL OF SCIENCE Synaptomys cooperi often is reluctant to enter live traps. For example, Connor (1 959) caught only 38 bog lemmings during four years of study in the swampy habitats of the New Jersey Pine Barrens. By contrast, other populations are readily trapp able . Hundreds of S. cooperi were routinely trapped in two different kinds oflive traps (Rose et al. 1977) in damp and dry oldfields in eastern Kansas, where they reached densities of 42-65 per hectare (Gaines et al. 1977, Gaines et al. 1979). Clearly the name \"bog lemming\" is misleading because Synaptomys is not restricted to bogs or even to damp places. Synaptomys has been reported from areas of woody vegetation (Hamilton 1941, Coventry 1942, Connor 1959), moist grassy areas (Howell 1927, Stewart 1943, Smyth 1946, Burt 1928, Getz 1961), and from dry, southfacing grassy fields, such as in eastern Kansas (Gaines et al. 1977, Rose et al. 1977, Gaines et al. 1979). First described in 18 5 8 from specimens taken near Jackson, New Hampshire (Hall 1981), the generic name was given because Baird believed it to be a link(= synapse) between the lemmings (Lemmus) and the true mice(= mys). In 1895, investigators from the US Biological Surveys, led by A. K. Fisher, collected southern bog lemmings from cane brakes near Lake Drummond in Virginia's Dismal Swamp which Merriam (1896) described as a new species, Synaptomys helaletes. However, in his revision of the genus, Howell (192 7) demoted the tax on to a subspecies, S. cooperi he la Zetes, a decision accepted by Wetzel (1955) in his taxonomic study of S. cooperi. More recently, Wilson and Ruff (1999) recognize seven subspecies, including the isolated forms in Kansas, Nebraska, and the Dismal Swamp region of Virginia and North Carolina. Fisher collected other southern bog lemmings from the Dismal Swamp as late as 1898, but none was taken thereafter, despite the efforts of several investigators , including Charles 0. Handley, Jr., Smithsonian Curator of Mammals, who trapped some of Fisher's sites in 1953, and in other years and places, all without success. Handley (1979) and others (Meanley 1973, Taylor 1974) speculated that since no specimens had been collected since 1898, the Dismal Swamp subspecies might be extinct. However, Rose (1981 ), using pitfall traps placed under power lines in the northwest corner of the Great Dismal Swamp National Wildlife Refuge (GDSNWR), caught 13 specimens from three locations in 1980, laying to rest doubts about its existence. During the 1980s and early 1990s, my students and I conducted survey trapping at over 100 sites throughout southeastern Virginia for the Dismal Swamp southeastern shrew, Sorex longirostris fisheri, then a federally listed mammal; the southern bog lemmings reported here were taken in those same collections. These studies have revealed the Dismal Swamp subspecies, Synaptomys cooperi helaletes, to be widespread in appropriate habitats throughout southeastern Virginia, with populations extending west of the Dismal Swamp at least through Isle of Wight County. METHODS Both live and pitfall traps were used in our studies, with the latter being used more extensively. Systematic live trapping was conducted in the open habitats under a 40-m wide power line in the northwestern corner of the GDSNWR (Stankavich 1984 ). Fitch live traps (Rose 1973), set at 7.6-m intervals in two rectangular grids (0.38 and 0.40 ha), were tended for two days every two weeks from October 1980 to February 1982 . BOG LEMMINGS IN EASTERN VIRGINIA 155 Other live trapping in the following two decades, conducted throughout the region in a range of habitats, has yielded only one other Synaptomys with live traps, except for an (unpublished) study conducted by L. J. Ford in Suffolk during 1987-1988. Most information on distribution and relative abundance comes from pitfall traps set on 0.25-ha grids in a range of habitats in southeastern Virginia (Rose et al. 1990). Placed at 12.5-m intervals on a 5 X 5 grid, each pitfall trap was a #10 tin can placed in the ground flush with the surface and partly filled with water. Earlier studies (e.g., French 1980) had shown that southeastern shrews (and to a lesser extent, southern bog lemmings) are rarely taken in live or snap traps, necessitating the use of pitfall traps to collect distribution and status information on these species. In the initial study, funded by the Office of Endangered Species (Rose 1983, Everton 1985), 37 pitfall grids were set in a range of habitats centering on the GDSNWR. A later study (Padgett 1991 ), funded by the Virginia Department of Game and Inland Fisheries, added 29 grids, mostly placed at greater distances from the GDSNWR in an effort to learn the geographic extent of distribution of the Dismal Swamp southeastern shrew. Another 85 pitfall grids were set at a variety of sites in the region in surveys conducted between 1986 and 1995. Finally, current information on the western limit of distribution comes from a study conducted in 1992 on 14 grids set in the open habitats under powerlines in Isle of Wight County (Rose 2005). Specimens collected in pitfall traps were returned to the lab, measured, weighed and evaluated for reproductive condition, and then saved (mostly as skull and skeleton) . Most of these specimens now are in the collections of the Smithsonian Institution, with a few remaining in the teaching collection at Old Dominion University. Collectively, these surveys provide information on the habitats and extent of distribution of southern bog lemmings in southeastern Virginia. RESULTS Live trapping Biweekly trapping for 17 months on the two live trap grids in the GDSNWR yielded 13 bog lemmings, two on Grid 1 and 11 on Grid 2 (Stankavich 1984). On Grid 2, none was caught until the 10 month, and then all were captured within a period of a few weeks. However, bog lemmings were known to be present from the start because they produce distinctive bright green bullet-shaped fecal pellets, plus they strip and eat the green outer covering from the softrush, Juncus ejfusus, leaving behind the spaghetti-like bits of pith. Ford's year-long mark-and-release study was conducted on a large study grid in a regenerating clearcut near the intersection of Desert and Clay Hill Roads in Suffolk, on a site close to the GDSNWR. She caught several dozen each of bog lemmings and woodland voles (Microtus pinetorum) using modified Fitch live traps (Rose, 1994 ). For unknown reasons, the southern bog lemmings on this site were much more pron~ to entering live traps than the same species had been in Stankavich's (1984) study. The only other Synaptomys taken in live traps was an adult female collected early in 1999 in early successional habitat in a wetland bank now reverting to Dismal Swamp vegetation in southern Chesapeake. I I 156 VIRGINIA JOURNAL OF SCIENCE
5 citations
TL;DR: Ashellito et al. as mentioned in this paper used Geographic Information Systems (GIS) as a visualization tool to examine sea turtle mortalities in relation to the dredging of the Thimble Shoals Federal Navigation Channel.
Abstract: Between 2000 and 2003 there were an increased number of documented sea turtle mortalities related to hopper dredging in the channels of the Chesapeake Bay. A pilot study was undertaken to create a bathymetric surface and three-dimensional model of the Cape Henry Channel using Geographic Information Systems (GIS) as a visualization tool to examine sea turtle mortalities in relation to the dredging. In Fall 2003, the US Army Corps of Engineers dredged the Thimble Shoals Federal Navigation Channel, and a more refined model was developed using this data. This project examines the growing concerns over sea turtle mortality rates and dredging operations, as well as a description of the usage of GIS analysis, interpolation, and visualization methods as tools for examining turtle habitat and mortality issues. Future directions for incorporating G IS into attempts to reduce sea turtle mortality in dredging operations are then outlined. INTRODUCTION AND BACKGROUND The section of the Chesapeake Bay off the Virginia coast contains a series of Federal Navigation Channels that are periodically dredged by self-propelled hopper dredges. These dredges are suitable for all but hard materials and are, by far , the best suited dredges for offshore work (Herbich 2000). There are four main navigation channels in the lower Chesapeake Bay: York Spit, York River Entrance, Cape Henry Channel, and Thimble Shoals Channel. Cape Henry Channel and Thimble Shoals Channel mark the entrance to the Bay from the Atlantic Ocean. The Thimble Shoals and Cape Henry channels are congressionally authorized Federal projects located in the mouth of the Chesapeake Bay between Hampton Roads and the Atlantic Ocean. Thimble Shoals Channel is approximately 18288 meters long, 304.8 meters wide, with an original depth of 13.7 meters at mean low water (CENAO 1973) . The channel was constructed in 1914 and requires maintenance dredging once every 2-3 years. Cape Henry Channel is approximately 328 meters wide and 3.7 kilometers long, with an original depth of 12.8 meters at mean low water (CENAO 1980). Figure 1 shows the locations of the Thimble Shoals channel and a portion of the Cape Henry channel as they relate to the Chesapeake Bay coastline region. 1 Corresponding author, Department of Geography, 1 University Plaza, Youngstown State University, Youngstown, OH 44555. Phone: 330-941-3317. Fax: 330-941-1802. b.ashellito@ysu.edu 2 Phone: 757-201-7418 , keith.b.lockwood@usace.army.mil