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Matrix land cover types differ in permeability to animals moving between habitat patches, and animals may actually move faster across less-suitable areas. Marsh rice rats are wetland specialists whose dispersal crosses upland matrix. Our objectives were to (1) compare matrix permeability for the marsh rice rat among upland cover types, (2) compare permeability within versus outside perceptual range of the wetland, and (3) explore intrinsic and extrinsic features influencing matrix use and permeability. We quantified permeability of grassland, crop field, and forest to the marsh rice rat during 2011–2012, by marking rats in wetlands and estimating the slope of capture rate versus distance (0–95 m) into the matrix. We also compared permeability within (0–15 m) and beyond the perceptual range of rice rats, and tested whether age, sex, time, water depth, rice rat abundance, and vegetation density influenced matrix use and permeability. Permeability was greater for soybean fields than grassland or forest but did not appear to differ within versus beyond rice rats’ perceptual range. Matrix capture rates were higher early in the study and in times and locations with thick ground vegetation and high rice rat abundance in the wetlands. Rice rats captured in the matrix were younger than those in wetland patches. Our findings expand known matrix use by marsh rice rats, and support permeability being high in matrix types dissimilar to suitable habitat. Studying individual movements will help identify mechanisms underlying enhanced permeability in crop fields. more...

In addition to external oiling, marine oil spills may affect vertebrate animals through degradation of habitat; alterations in food web structure; and contamination of resources by toxic compounds, including polycyclic aromatic hydrocarbons. These processes are not well understood for vertebrates breeding and foraging in terrestrial ecosystems affected by oil, such as coastal marshes that were heavily oiled following the 2010 Macondo oil spill. Here, we review what is known about the ecological and physiological effects of oil exposure on vertebrates in general. We then apply these concepts to salt-marsh vertebrates, with special reference to our ongoing monitoring of impacts and recovery in the seaside sparrow (Ammodramus maritimus) and marsh rice rat (Oryzomys palustris) in Louisiana following the Macondo spill. more...

Three island populations of the marsh rice rat (Oryzomys palustris) found in Florida have been described as taxonomically unique; the Pine Island rice rat (O. p. planirostris) and Sanibel Island rice rat (O. p. sanibeli), originally described as subspecies, and the endangered silver rice rat (O. argentatus), originally described as a separate species. We aimed to resolve the phylogenetic relationships among these island populations and investigate their genetic distinctness with DNA sequence data from the mitochondrial control region and cytochrome-b gene. Using parsimony, maximum-likelihood, and Bayesian analyses, we estimated the phylogenetic relationships and genetic distances among the 3 island populations and 4 other described subspecies. Our mitochondrial DNA analyses indicate that the silver rice rat and Sanibel Island rice rat are genetically divergent from mainland populations, but the Pine Island rice rat is not. The silver rice rat and Sanibel Island rice rat may be genetically isolated due to geographic separation resulting in reduced gene flow. They have the potential to become distinct phylogenetic groups and eventually species. more...

As a non-invasive approach for sampling small mammals, track tubes may be especially useful in species occupancy studies that do not require marking of individuals. However, such studies may involve significant uncertainty in identifying many tracks to species. Using 37 study sites in eastern Alabama and Tennessee, we compared relative differences in detection probabilities with track tubes vs. live traps for Peromyscus (deermice), Oryzomys palustris (Marsh Rice Rat), and Sigmodon hispidus (Hispid Cotton Rat). In analyses that ignored identification uncertainty or that used false-positive occupancy models to address this uncertainty, track tubes and live traps had similar detection probabilities. When uncertain detections were omitted from analysis, effective detectability was lower with track tubes. False-positive occupancy modeling indicated that track-identification uncertainty could not be ignored, as there was a non-zero probability of false-positive detections. False-positive occupancy designs have high relevance to track-tube studies; in addition, such studies should ensure that track identification is done under the oversight of an experienced tracker. more...

Author(s): Merrill, Mary M.; Lord, Cynthia C.; Turner, E. Lynn; Boughton, Raoul K.; Hernandez, Felipe A.; Wisely, Samantha M. | Abstract: Feral swine in the United States are known to harbor both native and exotic Ixodid ticks. The expanding range, broad habitat use, high population potential, and large movements of feral swine may increase the distribution and density of certain tick species and tick-borne pathogens that can infect humans, livestock, and wildlife. This preliminary study was conducted to determine which tick species are present on feral swine as well as other mammals sympatric with feral swine in south-central Florida. We trapped large-, medium-, and small-bodied mammals at two study sites, Kissimmee Prairie Preserve State Park and MacArthur Agro-ecology Research Center, from February to May of 2014. We examined mammals for ticks and conducted drags for host-seeking ticks. We trapped five mammal species (feral swine, Florida mouse, marsh rice rat, Virginia opossum, and northern raccoon). From these animals we identified four native tick species (Amblyomma americanum, A. maculatum, Dermacentor variabilis, and Ixodes scapularis) and one exotic to the United States (A. auricularium). We also obtained carcasses of nine-banded armadillos in Brevard County, on which we found A. auricularium. This is the first report of I. scapularis in Okeechobee County and A. auricularium in Brevard and Highlands Counties. All four native tick species are known disease vectors. These data reiterate that many mammals that share habitat with livestock and commonly contact humans are hosts to many ticks of medical and veterinary importance. Coupled with the population, distribution potential, and movement of feral swine, the diversity of ticks found in this study highlights the need for further research on the ability of feral swine to host and distribute ticks and tick-borne pathogens among wildlife, livestock, and humans. more...

Although the swimming behavior of Oryzomys palustris has been described, little is known about how long this species will remain in an area that is inundated by several centimeters of water. This study documents the response of an O. palustris population to habitat inundation in a coastal prairie locality of southeastern Texas. During a mark-recapture study conducted during 2002 and 2003, we live- trapped O. palustris on a grid in an area that experienced prolonged ($5 mo) inundation during 2 of our 6 quarterly trapping periods. We describe a trapping technique, using foam rafts to support rodent live-traps, that is suitable for use in inundated areas. Despite long-term inundation, little available refuge, and an apparent complete turnover of the population, we estimated population densities of ca. 29 individuals per hectare during inundation, only a moderate decrease from the higher levels encountered before and after inundation. RESUMEN—A pesar de que se ha descrito el comportamiento natatorio de Oryzomys palustris, se sabe poco sobre cuanto tiempo permanece esta especie en un a inundada por varios cento ´metros de agua. Esta investigacion documenta la respuesta de una poblacion de O. palustris a la inundacion de habitat en un llano costero del sureste de Texas. Durante un estudio de marca-recaptura realizado durante el 2002 y el 2003, capturamos vivos los O. palustris, en una parcela de un area que sufrioinundacion prolongada ($5 meses), durante 2 de nuestras 6 sesiones trimestrales de trampeo. Describimos una tecnica de trampeo usando balsas de unicel para sostener trampas para roedores, que son utiles para usar en a inundadas. A pesar de la prolongada inundacion, la falta de refugio disponible y un aparente cambio completo de la poblacion, estimamos una densidad poblacional de aproximadamente 29 individuos por hectarea durante la inundacion , solo una moderada disminucion del nivel mas alto encontrado antes y despues de la inundacion . more...

The ectoparasites of a small mammal community within an intertidal zone in the upper Gulf coast region of Texas were studied to assess the seasonal variation in abundances of the mite Gigantolaelaps mattogrossensis (Fonseca) (Acari: Laelapidae) on the marsh rice rat, Oryzomys palustris (Harlan). Further study into the ecology and dynamics of this parasite-host relationship was deemed to be necessary to expand the understanding of these potential participants in the ecology of Bayou Hantavirus, an important causative agent of Hantavirus pulmonary syndrome. The objective of this study was to determine the effects of five predictor variables on mite abundance: prevalences of hosts, relative humidity, precipitation, temperature, and length of daylight. Mite abundance was modeled as a function of the five variables with analyses of variance and multiple regressions; however, because the predictor variables pertain to the sampling period rather than to the individual rodent host, the effective sample size was small and thus the sums of squares and cross products matrix was singular. We therefore developed and used a new method for estimating regression coefficients based on the "noise-addition method" (random residual variation) combined with a bootstrap step converting the reduced rank data to full rank, providing realistic estimates of confidence intervals for the regression statistics. The population abundances of mites fluctuated significantly across collecting periods. Humidity and precipitation were the most influential variables in explaining the variation in abundances of mites. Model interpretation suggests that G. mattogrossensis is a nidicolous parasite. These results provide a baseline understanding of the seasonal interactions between parasite and host. more...

Low levels of genetic variation are thought to contribute significantly to the higher extinction rates of endemic island populations compared to their mainland counterparts. We used six microsatellite loci to compare the genetic structure of the endangered silver rice rat (Oryzomys argentatus) population in Saddlebunch Key, Florida to the mainland population of the closely related marsh rice rat (Oryzomys palustris natator) in Everglades National Park. Allelic richness and gene diversity are significantly lower in Saddlebunch Key than in the larger mainland population, and the two populations are significantly differentiated as measured by both F-statistics and Bayesian clustering methods. These findings support the classification of the Keys population as a “distinct vertebrate population” by the U.S. Fish and Wildlife Service. Current gene diversity (H E) is higher than expected under mutation-drift equilibrium in Saddlebunch Key, indicating a genetic bottleneck. The Keys population also exhibits a mode shift in its allele frequency distribution which suggests a very recent bottleneck has occurred and is consistent with reports of recent population declines. Although habitat loss and exotic species pose a more immediate and serious threat to silver rice rats, the continued loss of genetic variation may contribute to their long-term extinction risk due to inbreeding or by lowering the population’s ability to adapt to future environmental changes. The protection of habitat and the removal of introduced predators and competitors may help increase the population size of silver rice rats and lower their risk of extinction, both from a demographic and a genetic perspective. more...

Oryzomys palustris (marsh rice rat) and Microtus pennsylvanicus (meadow vole) cohabit coastal marshes in the mid-Atlantic US. Both were live-trapped for 23 months at two tidal marsh sites in Virginia to assess their demography near the margins of their distributions. In the presence of dense vegetation, population dynamics of the two species were seasonal and positively correlated, with densities declining through the winter. At the more sparsely vegetated site, densities of both species were lower, and densities of M. pennsylvanicus were negatively correlated with those of O. palustris. Patterns of reproduction differed between the species. O. palustris was reproductively most active in summer and least so in winter, whereas female M. pennsylvanicus decreased reproductive activity during summer. more...

Hispid cotton rats (Sigmodon hispidus) occur primarily in grass-dominated habitats. These habitats abut tidal wetlands along the Gulf and Atlantic coasts of the United States occupied by the marsh rice rat (Oryzomys palustris). Few data document whether cotton rats also occupy wetlands and whether interspecific interactions exist with rice rats. We used livetraps to sample 4 grids that each encompassed wetland and upland habitats near Galveston, Texas. Cotton rats occurred in both upland and wetland habitats. Density of cotton rats was lower in wetlands; their residence time was less in wetlands, which perhaps indicated poorer survival or movement to uplands. Sex ratio, proportion reproductive, and age structure, however, did not differ between upland and wetland habitats. Density of cotton rats and rice rats was negatively correlated. Such density compensation coupled with differences in diel activity and diet minimizes potential for interspecific competition. more...

The roles of photoperiod, melatonin, and the pineal gland in regulating the magnitude of compensatory gonadal hypertrophy (CGH) and other reproductive and non-reproductive organ growth during post-weaning development were examined in the marsh rice rat Oryzomys palustris. Juvenile rice rats of both sexes were left gonadally intact (control group) or unilaterally castrated (ULC) and housed on 12L:12D, 14L:10D, or 16L:8D. Within a photoperiod (14L:10D and 16L:8D, but not 12L:12D), growth of the remaining testis, but not the remaining ovary, as well as several additional organs in both sexes were significantly affected, suggesting that the compensatory hypertrophy of the testis is photoperiod-dependent. There was no effect of testis asymmetry on CGH as ULC of either testis in rice rats housed on 14L:10D resulted in a comparable increase of CGH. Melatonin implants in rice rats maintained on 16L:8D had little to no effect (CGH included) on most parameters examined. Both melatonin implants and pinealectomy (separate experiments) in rice rats transferred to 12L:12D prevented short photoperiod-induced effects on CGH, the growth of the reproductive organs and the Harderian glands. Evening melatonin injections had a significant inhibitory effect on the growth of the remaining testis (no CGH was observed) and all other parameters measured. Lastly, ULC did not alter the percentage of males which successfully mated compared to intact animals. Taken together, these data suggest that photoperiod, melatonin, and the pineal gland can affect and regulate reproductive (e.g., CGH in some cases) and non-reproductive growth during postnatal development in the marsh rice rat. more...

Dispersal among suitable habitat patches could be crucial to the regional persistence of wetland species. Dispersal success of animals will depend, in part, on the distance from which they can detect suitable habitat (ie, perceptual range). We investigated the perceptual range of marsh rice rats Oryzomys palustris Harlan, 1837 during the wet season in a region of central Florida characterized by small, isolated depression marshes. O. palustris had a limited perceptual range ( more...

To examine the interactions between age and photoperiod on reproduction and spleen weights, we exposed adult male and female rice rats of various ages to photoperiods of 16:8-h light-dark photoperiods (16L:8D) or 12L:12D. After 10 wk, animals were killed and the following data were recorded: weights of testes, seminal vesicles, uterus, ovaries, body, and spleen and, in addition, vaginal patency. Young adult males displayed a greater degree of testicular and seminal vesicle regression in short photoperiods than did older males; the testes of most older males did not regress in response to short photoperiods. Spleen weight was unresponsive to short photoperiods in all males, but was affected by age. Females, however, exhibited reproductive organ regression and decreased vaginal patency in response to short photoperiods at all ages examined. Body weights were affected by photoperiod in young females, and, as in males, photoperiod had no effect on spleen weights. These data suggest that the reproductive response to photoperiod in adult male rice rats declines with age, whereas in adult females it does not. more...

A comparative hierarchical approach was used to examine allozymic variability within and among nine populations of Oryzomys palustris (marsh rice rat) and seven populations of Peromyscus leucopus (white-footed mouse) from the Virginia barrier islands and southern Delmarva Peninsula. O. palustris is an effective disperser over water and is present on 21 of 24 islands. In contrast, P. leucopus is a less effective disperser over water and occurs on only four of 24 islands. Of 31 loci, four were variable in O. palustris ; six were variable in P. leucopus . The nine populations of O. palustris had an average heterozygosity of 2.4% with 6.7% polymorphic loci. For seven populations of P. leucopus , the average heterozygosity was 3.6% with 12.3% polymorphic loci. Both species had lower levels of variation among mainland populations than among island populations. Populations of P. leucopus exhibited considerable genetic differentiation ( F ST = 0.180) and lower levels of gene flow ( N m = 1.14) among populations, whereas O. palustris had moderate levels of differentiation ( F ST = 0.135) and higher levels of gene flow ( N m = 1.60) among populations. Mantel tests indicated a significant relationship between genetic distance and geographic distance in Oryzomys but not in Peromyscus . more...

In the United States, Bayou virus (BAYV) ranks second only to Sin Nombre virus (SNV) in terms of hantavirus pulmonary syndrome (HPS) incidents, having been confirmed in cases from Texas and Louisiana since its discovery in 1994. This study on BAYV infection among sympatric, non-oryzomyine rodents ("spillover") in Freeport, TX, is the first to link patterns of hantavirus interspecific spillover with the spatiotemporal ecology of the primary host (marsh rice rat, Oryzomys palustris). Mark-recapture and/or harvest methods were employed from March 2002 through May 2004 in two macrohabitat types. Rodent blood samples were screened for the presence of IgG antibody to BAYV antigen by IFA after which Ab-positive blood, saliva, and urine were analyzed for the presence of viral RNA by nested RT-PCR. From 727 non-oryzomyine captures, five seropositive (but not viral RNA positive) individuals were detected: one each of Baiomys taylori, Peromyscus leucopus, and Reithrodontomys fulvescens; and two Sigmodon hispidus. Spillover hosts were not associated with macrohabitat where O. palustris abundance, density, or seroprevalence was highest. Rather, spillover occurred in the macrohabitat indicative of greater overall disturbance (as indicated by grazing and exotic plant diversity) and overall biodiversity. Spillover occurred during periods of high seroprevalence detected elsewhere within the study region. Spillover locations differed significantly from all other capture locations in terms of percent water, shrub, and grass cover. Although greater habitat and mammal diversity of old-fields may serve to reduce seroprevalence levels by tempering intraspecific contacts between rice rats, greater diversity also may create an ecologically opportunistic setting for BAYV spillover. Impacts of varying levels of disturbance and biodiversity on transmission dynamics represent a vastly uncharacterized component of the evolutionary ecology of hantaviruses. more...

Elemental composition of soil, herbaceous and woody plant species, and the muscle and liver tissue of two common small mammal species were determined in a wetland ecosystem contaminated with Ni and U from nuclear target processing activities at the Savannah River Site, Aiken, SC. Species studied were black willow ( Salix nigra L.), rushes ( Juncus effusus L.), marsh rice rat ( Oryzomys palustris), and cotton rat ( Sigmodon hispidus). Two mature trees were sampled around the perimeter of the former de facto settling basin, and transect lines sampling rushes and trapping small mammals were laid across the wetland area, close to a wooden spillway that previously enclosed the pond. Ni and U concentrations were elevated to contaminant levels; with a total concentration of 1,065 (+/- 54) mg kg(-1) U and 526.7 (+/-18.3) mg kg(-1) Ni within the soil. Transfer of contaminants into woody and herbaceous plant tissues was higher for Ni than for U, which appeared to remain bound to the outside of root tissues, with very little (0.03 +/- 0.001 mg kg(-1)) U detectable within the leaf tissues. This indicated a lower bioavailability of U than the cocontaminant Ni. Trees sampled from the drier margins of the pond area contained more Ni within their leaf tissues than the rushes sampled from the wetter floodplain area, with leaf tissues concentrations of Ni of approximately 75.5 (+/- 3.6) mg kg(-1) Ni. Ni concentrations were also elevated in small mammal tissues. Transfer factors of contaminants indicated that U bioavailability is negligable in this wetland ecosystem. more...

A total of 237 rodents was collected in 4 regions of South Carolina from July 1994 through December 1995. Eight species were collected, including cotton mouse, hispid cotton rat, eastern woodrat, marsh rice rat, white-footed mouse, eastern harvest mouse, golden mouse, and black rat. Of the 1,514 ticks recovered from these hosts, Ixodes minor Neumann, including larvae, nymphs, and adults, was the most abundant species, representing 54% of the total. Only immature stages of other tick species were found, including larvae and nymphs of Dermacentor variabilis (Say), Amblyomma maculatum Koch, Ixodes affinis Neumann, and Ixodes scapularis Say. All 5 tick species parasitized cotton mice, cotton rats, and woodrats, which were the most important small mammal hosts for ticks at the localities studied. Rice rats were hosts of A. maculatum, D. variabilis, and L. minor. Amblyomma maculatum was more strongly associated with cotton rats than other rodent species. Ixodes scapularis was most strongly associated with cotton mice, and I. minor was more strongly associated with both woodrats and cotton mice than other species of rodents. Ixodes minor parasitized hosts in the Coastal Zone only, where among spirochete-infected hosts, it was present in significantly greater numbers than other ticks. Furthermore, I. minor was the only tick species that showed a statistically significant positive association with spirochetal infection in rodents. More I. affinis parasitized spirochete-infected hosts than I. scapularis, but fewer than I. minor. The findings discussed herein provide evidence that implicates I. minor as the possible primary enzootic vector of the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt and Brenner in the Coastal Zone of South Carolina. They also indicate that the high level of B. burgdorferi infection in rodents from this region may be a function of the combined involvement of I. minor, I. affinis, and I. scapularis in the enzootic transmission of the spirochete. more...

Tree islands in the Everglades prairie provided a unique opportunity to study how patch dynamics affect population processes in two small mammal species, the marsh rice rat and hispid cotton rat. We assessed the effect of island size and water on density, survivorship, reproduction, and movement in both these species. Rice rats had the highest densities on the small islands, while survivorship and reproductive activity was not affected by island size. Cotton rats had the highest densities and reproductive activity on large islands, while survivorship and reproduction was not affected by island size In both species, the highest proportion of animals moved from small islands. more...

Small mammals are key consumers in the marsh food web and could serve as indicators of a marsh's potential to support higher-level predators. We studied how small- mammal occupancy varied among plant communities in coastal Louisiana freshwater marshes. We sampled small mammals at 36 sites on 4 different occasions during the late spring in freshwater marshes of the Mandalay National Wildlife Refuge, LA. Mammalian diversity was low; we captured only Oryzomys palustris (Marsh Rice Rats). Occupancy modeling revealed a positive association between Marsh Rice Rat site occupancy and Sagit- taria lancifolia (Bulltongue Arrowhead) biomass. Our data suggest that subtle changes in plant-species composition within a marsh may affect the distribution of the most common small mammal in the ecosystem. more...

Pineal melatonin content was examined under four different photoperiods (10L:14D, 12L:12D, 14L:10D, and 16L:8D) in adult female rice rats (Experiment 1). Pineal melatonin was basal during the light and increased beginning 1 hr after lights off. Within 2 hr after lights off, melatonin increased to levels that were maintained throughout the dark period. In all but one photoperiod (10L:14D), melatonin remained elevated prior to light onset and decreased markedly within one hour after lights on. In addition, the duration of pineal melatonin was inversely related to the length of the photoperiod. In Experiment 2, the time course of pineal melatonin content on 16L:8D was examined every 20 min during the first hour after lights off and the first hour after lights on. Melatonin content increased gradually during the first hour and decreased markedly within 20 min after lights on. These data show that pineal melatonin in female rice rats is regulated by photoperiod. more...

Nesting success of Forster’s Terns (Sterna forsteri) was examined on two small islands in the Cedar Island area of North Carolina. Forster’s Terns laid an average of 2.1 eggs per nest (n = 50) on Chainshot Island and 2.1 eggs per nest (n = 43) on Harbor Island in clutches that consisted of 1 to 3 eggs. On Chainshot Island every egg (n = 107) was lost to predation. On Harbor Island, 72 of 92 eggs were preyed upon. A trapping program, initiated on both islands, yielded 32 Marsh Rice Rats (Oryzomys palustris). Stomach contents of 23 rats were inspected, with 92.3% from Chainshot Island and 70% of the stomachs from Harbor Island containing yolk and feathers of Forster’s Terns. more...

Growth rates and/ or dynamics of body mass for the hispid cotton rat ( Sigmodon hispidus ), fulvous harvest mouse ( Reithrodontomys fulvescens ), and marsh rice rat ( Oryzomys palustris ) were determined from field data. Significant sexual dimorphism was exhibited by all three species when based on average body mass. Growth rates were categorized by sex, season, and size class for Sigmodon and Reithrodontomys. Female Sigmodon grew faster than males, there were no seasonal differences in growth rate for cotton rats, and Reithrodontomys exhibited increased spring female growth and overall decreased growth rate with increased size. The lack of seasonal differences in growth rates was attributed to the mild climate of the area and the continuous availability of resources. Growth rates determined in the field were, on the whole, much lower than growth rates obtained from laboratory colonies. more...

Rice rats were studied for four years by grid trapping in a tidal marsh on the northern Gulf of Mexico. Preliminary trapping indicated that marshes are preferred over other coastal habitats. Population densities fluctuated from spring lows of about 2/ha to highs of about 25/ha in the autumn and early winter. Reproduction occurred throughout the year, the major season being late spring to late autumn. Recruitment of juveniles was at a maximum from May to September. Males were more abundant than females in population samples, and had a higher mean body weight. This was because weight classes of 40 g and below were slightly skewed in favour of females and weight classes above 40 g heavily favoured males. The survival rate was low, with less than 20% of animals marked remaining on the grids for more than three months. Maximum longevity was 24 months. Results are compared to those of previous studies done on an offshore island and in the Florida everglades. more...

Host attraction studies of adult Culicoides furens and C. hollensis were conducted in a Spartina salt marsh in Carteret County. North Carolina, USA. The attractancy of domestic animals (Japanese Quail, white rat, White Leghorn chicken and New Zealand white rabbit) was determined using animal-baited traps in a Latin square experimental design. Paired comparisons of domestic animals with wild live-trapped animals from the marsh (Hispid Colton Rat. Mallard Duck, Virginia Opossum, Raccoon and Marsh Rice Rat) were made using the same type of traps. In general, the degree of attractiveness of the animals to C. furens and C. hollensis was related more to the size of the animal than to the kind of animal. There were little differences in the attractancy of domestic and wild animals, It was concluded that C. furens and C. hollensis have a wide host range and should not be classified as either ornithophilic or mammalophilic, Catches of Culicoides by animal-baited traps were poorly correlated with catches in nearby emergence and sticky cylinder traps. more...

The swimming ability of cotton rats and rice rats from several localities in Florida and Mississippi was compared. Rice rats freely swam a 2-m barrier separating two small “islands,” making better than 20 times the number of crossings made by cotton rats. Some cotton rats (26%) never swam the barrier during the 2-day test period, but all rice rats did. In general, cotton rats from Florida, especially ones from a barrier island, swam more frequently than did cotton rats from Mississippi. Rice rats from all localities were approximately equal in their tendency to swim. All crossings by rice rats and most by cotton rats were made during darkness. The fur of rice rats was more water repellent than that of cotton rats. Air trapped between hairs increased the buoyancy of the rice rats and reduced heat loss in water. Even with twice the body weight, cotton rats exhibited a significantly greater decrease in core body temperature when placed in 15°C water for 40 min than did rice rats. While swimming, both species used mainly the hind feet for propulsion and held the front feet close to the body. Rice rats swam faster than cotton rats, frequently swimming underwater for more than 10 m. Cotton rats never swam underwater, although they would momentarily submerge when they jumped from a platform. Semiaquatic adaptations appear to be important components of niche segregation in these sympatric rodents. more...

This study investigated (1) how individuals respond to patchy environments, and (2) how these responses may collectively produce attributes that characterize local and regional populations. Mark-recapture trapping was used to monitor populations of Peromyscus gossypinus, Sigmodon hispidus , and Oryzomys palustris occurring on a constellation of six discrete patches (tropical hardwood hammocks) in the Everglades of south Florida. In the wet season the populations were compressed onto the hammocks where the three species occurred together at high densities in 1975. In 1976 there were fewer Peromyscus and Sigmodon in the wet season than in the other years, while the density of Oryzomys matched its 1975 level. All reproduction occurred in the wet season. In the dry season Sigmodon moved off the hammocks and occupied the prairie, Oryzomys disappeared (presumably to seek refuge in mesic sites off the study area), and Peromyscus remained on the hammocks (although frequently caught on the prairie). Sigmodon and Oryzomys recolonized the hammocks at the beginning of the wet season, although no individuals captured on the hammocks in 1975 returned in 1976. Of the three species, Oryzomys showed the greatest degree of interhammock movements; Peromyscus was the least vagile. Interhammock movements by individual Peromyscus were dependent on sex, season, and hammock size. The largest hammock, 0.25 ha, apparently promoted and accomodated fewer vagrant Peromyscus than the smaller hammocks. Saturation of habitat appears determined by the interplay of the size and spacing of the hammocks and the structure of each species population. more...

These karyotypes are gift of Dr. G.S. Khodr and G. Cadena of San Antonio, Texas and were prepared from skin fibroblast cultures of two animals collected by O.S. Parker and T. Urban in Cameron County, Texas. The karyotypes of this species differ from those presented previously (Vol.3, Folio 117) in the structure of sex chromosomes. Moreover, the present animals are brown as opposed to the grey subspecies from Louisiana and Florida. The present species was formerly designated Oryzomys couesi. more...

SYNOPSIS. Eimeria kinsellai sp. n. is described from the marsh rice rat Oryzomys palustris from Florida. Its ellipsoidal oocysts were 23–31 by 15–19 μ (mean 26.7 by 16.9 μ). One to four polar granules were present but an oocyst residuum was absent. The sporocysts were 12–15 by 7–9 μ (mean 13.9 by 8.1 μ), and sporocyst residua were present. more...

Eimeria palustris sp. n. and Isospora hammondi sp. n. are described from the marsh rice rat, Oryzomys palustris, from Alabama. The ellipsoidal oocysts of E. palustris measure 19 to 28 by 16 to 21 /L (mean 23.7 by 18.1 u), and sporocysts are 12 to 15 by 7 to 9 A (mean 13.6 by 7.5 4). A polar granule is present, but an oocyst residuum is absent. Prepatent and patent periods averaged 3.3 and 4.7 days, respectively. The ovoid oocysts of I. hammondi measure 24 to 30 by 16 to 21 ,u (mean 27.1 by 18.9 a/), and sporocysts are 13 to 18 by 11 to 15 A (mean 16.0 by 11.9 I/). The oocysts lack a micropyle, oocyst residuum, polar granule, and Stieda bodies. Prepatent and patent periods averaged 5.3 and 3.5 days, respectively. This is the first report of prepatent and patent periods of an Isospora species from a rodent. Nineteen marsh rice rats, Oryzomys palustris (Harlan), were trapped in the Tuskegee National Forest, Macon County, Alabama, and examined for coccidia at the Regional Parasite Research Laboratory, ARS, USDA, Auburn, Alabama. Nine of these animals harbored coccidian oocysts. Two species of coccidia were distinguished-one of the genus Eimeria and one of the genus Isospora. Both are previously undescribed and are described herein as new more...