Trapping Grids Research Articles

Diggings as a Population Index for the Eastern Barred Bandicoot

Quick, efficient techniques for monitoring populations are vital in ecological studies. Transect methods provide one possible means of monitoring local numbers. We investigated the usefulness of the diggings of the eastern barred bandicoot (Perameles gunnii), an endangered, small-medium sized marsupial of southeastern Australia as an index of population size using a modification of the kilometric index. Total diggings and mean transect diggings were correlated with P gunnii numbers on 2 trapping grids in southeastern Tasmania. When grids were combined, mean transect diggings provided a reasonably accurate estimate of animal numbers. We suggest that digging counts provide a quick and efficient method for monitoring changes in local populations of P. gunnii.

Sex-related spatial kin structure in a spring population of grey-sided voles Clethrionomys rufocanus as revealed by mitochondrial and microsatellite DNA analyses.

Polymerase chain reaction-directed mitochondria (mt) and microsatellite DNA analyses were performed to examine the kin structure in a spring population of grey-sided voles Clethrionomys rufocanus in Hokkaido, Japan. The spatial distribution of 81 voles in a trapping grid (about 1 ha) was estimated by using the catch-mark-release method. DNA samples were extracted from the toes clipped for individual identification. Maternal lineages of voles were unequivocally determined by the mtDNA haplotypes, as identified by nucleotide sequencing of the control region. Relatedness between individuals was estimated based on the genotype and allele frequencies at several microsatellite loci. Although the distribution of voles was uniform within the grid, neighbouring females were frequently from the same maternal lineage. Relatedness values between females correlated negatively with geographical distances. Combination of the two molecular markers revealed four clusters of closely related, matrilineal females in the population, whereas no such cluster was apparent in males. The present study first demonstrated a sex-related spatial kin structure in a natural population of the grey-sided vole.

Three-dimensional distribution of Sitophilus granarius (L.) (Coleoptera: Curculionidae) in wheat influenced by the synthetic aggregation pheromone

The distribution pattern of Sitophilus granarius released in different weevil densities in a large bulk of ca. 350 kg wheat was investigated using a three-dimensional trapping grid of surface and bottom pitfall-traps, as well as probe-traps beneath the surface at eight different trap locations. Baiting the surface, bottom and pitfall traps of a single trapping location each with ca. 6000 ng of the synthetic aggregation pheromone sitophilate considerably changed the distribution of the weevils. In the presence of the pheromone, the overall catch of all trap sites combined was reduced at lower weevil densities. The insects tended to stay in the interkernel space beneath the surface. The aggregation pheromone acted more as an arrestant than an attractant chemical. The sex specific effects and the behavior modifying character of sitophilate in the granary weevil is discussed in relation to practical application, which may lead to an improvement of monitoring systems in the field of stored product protection.

The effect of bait type, tunnel design, and trap position on stoat control operations for conservation management

Abstract The effectiveness of trapping stoats (Mustela erminea) using different bait types, tunnel designs, and trap positions was investigated during and following stoat population irruptions in Eglinton Valley, Fiordland, and Hawdon Valley, near Arthur's Pass, in the summers of 1990/91, 1991/92, and 1992/93. Each summer, different baits were used. Comparisons were made between broken, whole and hard boiled eggs, tinned cat food, possum flesh, dead mice, and synthetic lures based on the anal sac secretions of mustelids. Broken and hard boiled eggs were the most effective and practical lures. Tunnels with partially camouflaged traps were no more effective than those with wooden bases and visible traps, which are faster and easier to check in the field. Single‐entrance tunnels caught about as many stoats as the traditional double‐ended ones. More stoats, especially males, were caught at the edges of a trapping grid than within it.

Failure to Detect Senescence in Persistence of Some Grassland Rodents

Several recent papers raise the question of how frequently senescence is detectable in survival estimates from natural populations of mammals. If animals do not age, the probability of disappearance is constant through time. This null hypothesis leads to the prediction that lengths of residence on a trapping grid, censused monthly, will follow a geometric distribution. After testing for survival differences between sexes and among seasons, I compared lengths of residence (persistence) from capture—recapture data for five species of small rodents in an old—field habitat near Lawrence, Kansas, USA to geometric distributions. Gender did not influence persistence on the grid for any species, but persistence of Microtus ochrogaster and Reithrodontomys megalotis varied significantly with season. All species showed a tendency for high rates of disappearance in the 1st mo after individuals were marked. When the analysis was limited to individuals residing on the area for at least 1 mo, neither Peromyscus maniculatus, P. leucopus, nor Sigmodon hispidus departed significantly from the geometric model. Seasonal analysis of Reithrodontomys megalotis was precluded by small samples, but data for all seasons combined seemed to indicate age— (or persistence—) specific rates of disappearance, as did M. ochrogaster, except those first captured in spring. To identify which patterns were consistent with senescence, I regressed rates of disappearance against persistence, testing for positive slope. Only those M. ochrogaster first captured in winter and autumn exhibited senescence by these criteria, despite disappearance rates of R. megalotis that increased sharply beyond persistence of 5 mo. The regression test for P. maniculatus indicated senescence even though the geometric test failed to indicate persistence specificity. The regression method alone is not a reliable test of senescence, because if does not incorporate variances of estimated probabilities of survival. Any approach derived from horizontal life tables potentially confounds seasonality with aging, making determination of senescence equivocal. In my data there is little convincing evidence that survival in the wild decreases with age in these rodents.

Population dynamics of, and habitat use by, Austrlian native rodents in wet sclerophyll forest, Tasmania I. Rattus lutreolus velutinus (Rodentia : Muridae)

A local population of velvet-furred rats, Rattus lutreolus velutinus, was studied for 15 months in wet sclerophyll forest in south-eastem Tasmania using mark-recapture techniques. Individuals in the trappable population were readily caught with 90% of captures being recaptures (73 individuals caught 706 times). During winter and the summer breeding season, all individuals had an equal likelihood of recapture, irrespective of sex, age, season or previous capture history. Habitat use was investigated by analysing floristic and structural variation within a 4-ha trapping grid using TWINSPAN. Four heterogeneous habitat groups were defined and population data are compared among these groups. Areas of densest ground cover were preferred by R. 1. velutinus; open areas were avoided. Throughout the study, female rats were captured in the areas with most cover to 50 cm in height; during winter, males were caught in areas of the trapping grid with more sparse ground cover, in lower numbers than females. At the onset of breeding in summer, numerous males were captured in the areas of thickest ground cover occupied by females. These data are discussed in relation to social spacing, habitat utilisation and female choice.

THE EFFECTS OF DIFFERENT GRAZING REGIMES ON THE POPULATION DYNAMICS OF SMALL MAMMALS IN THE EASTERN CAPE

SUMMARY Four permanent trapping grids on predominantly sweet grass-bush study plots and subjected to different grazing regimes, were monitored from June 1991 to July 1992. The diversity and population density of small mammals on these grids were affected by the pattern of animal stocking and grazing types. Only two species, Rhabdomys pumilio and Mastomys natalensis were trapped. Sites undergoing rotational resting, and those grazed by cattle, supported more rodents than constantly grazed ones and those grazed by sheep. Other environmental factors, excepting drought, had lesser impacts on the small mammal populations. The seasonal recruitment and breeding of the small mammals was affected by grazing whereas sex ratios appeared unaffected. The drought of 1991–92 was obviously a contributory factor to low small mammal numbers.

Distances Moved by Stephens' Kangaroo Rat (Dipodomys stephensi Merriam) and Implications for Conservation

Movements by Dipodomys stephensi were assessed by live-trapping and radiotelemetry to evaluate consequences of habitat fragmentation for this endangered species. The median of the maximum distances moved between captures was 29.2 m for the 557 individuals with ≥2 captures. The median distance between first and last monthly home-range centers was 17.6 m for individuals captured in ≥2 months. Males moved longer distances than did females; lactating females were especially sedentary. Dispersal distances were similar for juveniles and adults and for two sites with different geometries of habitat patches. The median distance between first and last home-range center of adults radiotracked for 15–127 days was 9.5 m, indicating stable home ranges. However, radiotracked individuals moved greater maximum distances than most live-trapped individuals apparently moved over a lifetime. Much dispersal, therefore, occurs within an area about which animals have knowledge. This should facilitate habitat selection and decrease the cost of dispersal in terms of fitness. The frequency distribution of maximum dispersal distances underestimated the frequency of moves >400 m. Two processes may have contributed to this bias. First, the frequency of long-distance moves was underestimated because we measured dispersal away from a single grid. Second, our trapping grids were located in homogeneous habitat without dirt roads, which appear to facilitate long-distance movement. Unvegetated corridors show promise for increasing the connectedness of local populations of D. stephensi . Connectedness should be considered in management of endangered species such as D. stephensi , because the expected persistence of metapopulations is sensitive to the extent of dispersal and the fitness of dispersers.

Estimating population density of moles Scalopus aquaticus using assessment lines

Density was estimated for three populations of eastern moles Scalopus aquaticus Linnaeus, 1758, in South Carolina using a trapping grid and assessment lines. Assessment line data were based upon the repair of holes punched into surface tunnels of the animals. Using a new method of analysis for assessment line data, a logistic curve was fitted to the data.

Differential Effectiveness of Standard and Long Sherman Livetraps in Capturing Small Mammals

Most studies of small-mammal populations rely on livetrapping, yet relatively few studies compare different types of traps. We placed one standard-length (22.9 cm) and one long (30.5 cm) Sherman livetrap at each station of a trapping grid in oldfield habitat in eastern Kansas and compared rates of capture of small mammals over a 5-year period (1985–1990). Nine of 10 species were captured more often in long traps. Of the five most commonly trapped species, only Sigmodon hispidus and Microtus ochrogaster varied seasonally in proportion of captures in long traps. Species having lower adult body mass were captured proportionately more often in long traps, suggesting that long traps might have more sensitive trigger mechanisms. However, long traps closed without capturing an animal significantly less often; furthermore, proportions of captures in the two types of trap did not differ among mass classes of S. hispidus or M. ochrogaster , so size differences alone cannot account for differential capture success. Not only were capture rates higher in long traps, but also mortality due to predators and winter exposure was lower.

A longitudinal study of Junin virus activity in the rodent reservoir of Argentine hemorrhagic fever.

We monitored Junin virus (JV) activity in rodent populations for 30 months at seven mark-recapture grids located in agricultural fields and adjacent roadsides and fence lines in endemic and nonendemic areas of Argentine hemorrhagic fever. Blood and oral swabs taken from rodents captured at five-week intervals were analyzed by enzyme-linked immunosorbent assay for JV antigen (Ag). Calomys laucha and C. musculinus were the most frequently captured rodents, making up 47% and 22% of captures, respectively. Of 41 Ag-positive captures, 37 were C. musculinus and four were C. laucha; 34 were from two trapping grids in the same locality. Antigen-positive Calomys were more frequently male (76%), and were found significantly more frequently among the oldest animals and the largest body mass classes. These patterns, combined with the greater mobility and higher frequencies of wounds among males than females, implicated horizontal transmission as the primary route of JV transmission between rodents. Seasonal maximum levels in JV prevalence (up to 25% of captured Ag-positive C. musculinus) occurred during periods of maximal population densities of Calomys. Spatial distribution of Ag-positive rodents reflected habitat preferences; most Ag-positive C. musculinus were captured from border habitats (roadsides and fence lines), and all Ag-positive C. laucha were captured in crop fields. These distinct, but previously undocumented, habitat preferences suggest that the disease in humans may be related to exposures to the primary reservoir species, C. musculinus, in border habitats rather than in crop fields.

A Tracking Technique to Locate Small Mammals at Low Densities

To optimize our livetrapping of low-density populations of lemmings ( Dicrostonyx kilangmiutak ) and voles ( Microtus oeconomus ) (0.2–0.4 animals/ha) in the Arctic tundra, we developed a powdered-slide tracking technique to determine if burrows were occupied. Painted microscope slides covered with talcum powder on a thin oil base were placed at all burrows on trapping grids, and only those burrows showing activity were trapped. Our capture success per trap tripled with this method in comparison with standard grid-stake trapping, and our effort per grid decreased by >50% after all burrows were initially located. This technique also should be useful in similar arid environments such as deserts, for obtaining relative indices of density, and for following toe-clipped animals.

The influence of trap residual odour on catching woodland rodents

Live trapping data on wood mice, Apodemus sylvaticus, bank voles, Clethrionomys glareolus, yellow-necked mice, A. flavicollis, and common shrews, Sorex araneus, collected from studies in an oak woodland in Surrey, were examined to see whether residual odour left in the trap by one individual affected subsequent re-entry by the same or another individual. Significantly more animals entered dirty traps than clean traps and there was a tendency for recaptures to occur in traps containing residual odour of a conspecific. Most data were obtained on wood mice and bank voles and these were examined further. In these species there was a tendency for recaptures to be in traps containing the odour of conspecifics of the same sex and breeding condition. There was no evidence of breeding males or females being attracted to traps containing odour of the opposite sex. The results are discussed with respect to animal density, the placement and density of traps within the habitat, and the social behaviour of the animals. An experiment, which involved moving each trap to the next trap station on the trapping grid after the first day of trapping, was carried out to try to separate an ‘odour effect’ from a ‘position effect’. The results were equivocal and further work on this is recommended. It is concluded that residual odour docs not significantly affect the results from live trapping studies on these species provided the ratio of traps to animals is high.

Does Supplemental Feeding of Red Squirrels Change Population Density, Movements, or Both?

Supplemental feeding increased the number of red squirrels ( Tamiasciurus hudsonicus ) captured on two trapping grids, leading Sullivan (Journal of Mammalogy, 71:579–590, 1990) to infer that the population density of residents had increased. This conclusion is questionable because the residency status of captured squirrels was unknown.

Notes on the Biology of the House Mouse, Mus domesticus, on the Yucatan Peninsula, Mexico

Notes on the Biology of the House Mouse, Mus domesticus, on the Yucatan Peninsula, Mexico

Man's Effects on Aquatic and Riparian Organisims in the Canyons of Canyonlands and Arches National Parks and Natural Bridge National Monument

This research was designed to assess the impact of a hiking trail or a four wheel drive road on our three focal groups (plants, aquatic animals and small mammals). Analyses in 1990 revealed large differences in species abundances and some instances of presence/absence differences among the three focal groups. Differences occurred both between the road right of way per se and nonroaded sections of the canyon bottom and between roaded and nonroaded sections of the canyon bottom. In 1990 we sampled small mammals and plants for 2.4 km up and downstream of the road terminus. In May, June, and July 1991 we extended sampled areas to approximately 4.8 km up and downstream of the end of the four wheel drive road. We also sampled aquatic organisms at Natural Bridges and in Canyonlands. In addition, we performed an experiment in which we placed screen mesh enclosures into the creek above and below Bates Wilson Campground, Canyonlands. This experiment was designed to assess sand infiltration rates and aquatic animal densities in areas lacking or possessing a road. Four small mammal trap grids (70 traps/grid) were trapped in the area lacking a road and in an area containing a road up Salt Creek. Each trap grid was trapped for four successive nights. Eight plant grids (4 up and 4 downstream of the road terminus) were examined for species composition and plant coverages. Each upstream grid consisted of fifty 1 m2 plots, while the downstream grids consisted of the same 50 plots plus 10 plots randomly located in the road right of way.

Habitat Use and Relative Abundance of Gray Squirrels in Southern Alabama

We studied habitat use and estimated relative abundance of gray squirrels (Sciurus carolinensis) in 3 habitats at the Solon Dixon Forestry Education Center, Covington and Escambia counties in southern Alabama, from January 1987 to September 1988. Three representative stands of even-aged pine, mixed pine-hardwood, and hardwood were selected for study, and a 50-station trapping grid was established in each. We captured 603 squirrels 1,586 times. Relative abundance was based on the minimum number of squirrels known alive. Squirrel abundance in hardwood and in mixed pine-hardwood habitat did not differ (P=0.47), but abundance in even-aged pine was lower (P<0.001) than either of the other 2 habitats. We measured 6 habitat variables in each study area. Moderately open understories with a dense shrub crown (vegetation between 1 and 5 m) component appear to be important to squirrel abundance. To determine habitat preference, we fitted 17 gray squirrels with radio transmitters. Narrow bands of hardwoods along ephemeral streams (i.e., hardwood stringers) were an important component of gray squirrel habitat in even-aged pine and mixed pine-hardwood stands. Forest management should include the retention of hardwood stringers within pine and mixed pine-hardwood stands

Feeding and Breeding Responses of Five Mice Species to Overwintering Aggregations of the Monarch Butterfly

(2) Large numbers of adult P. melanotis, with a significant bias of females, immigrated to trapping grids inside aggregations, established residency, and bred intensively throughout the winter. The other species also immigrated to the aggregations, but did not establish residency. On grids outside aggregations, individuals of all species established residency and showed comparatively little breeding throughout the winter. (3) We estimated an average of 6 5 live, moribund, and bird-damaged monarchs per m2 per night on the forest floor inside aggregations. Stomach content analyses indicated that P. melanotis inside aggregations fed exclusively on monarchs. Even though all five species scavenged some butterflies on grids outside aggregations, P. melanotis scavenged significantly more. (4) We tested two hypotheses to explain why only P. melanotis established residency on grids inside aggregations: (i) unique plant species compositions in overwintering sites rendered them suitable only to P. melanotis, and (ii) P. melanotis aggressively excluded the other species. We rejected the first hypothesis because the understorey vegetation on grids inside and outside aggregations did not differ significantly, and rejected the second because P. melanotis did not dominate the other species in experimental agonistic encounters.

Local Distribution of Termites in Mixed Grass Prairie

Subterranean termites (Reticulitermes sp.) attacked over 25% of 480 wooden structures (shelters for small mammal traps) present in grazed mixedgrass prairie between July 1985 and June 1989. This cattle-grazed pasture included upland, breaks, and lowland prairie and we report herein the distribution of Reticulitermes across these topoedaphic sites. Termites were most likely R. flavipes as this is the predominant species in this region of Kansas, although R. hageni is a slight possibility (R. W. Howard, pers. comm.). The study site was a 10.8-ha trapping grid (480 stations with 15 m between stations) established in a grazed mixed-grass pasture in SE14 Sec. 30, T lIS, R1OW, Lincoln Co., Kansas. Native vegetation in this region is classed as the bluestem-grama (Andropogon-Bouteloua) association of the mixed-grass prairie (Kiichler, 1974). Habitat categories were upland prairie (shallow soil above Cretaceous-aged limestone layers, n = 210 stations), limestone quarry (upland pits from which limestone was quarried earlier this century, n = 12), spoil bank (a mound of soil and rock from the excavation of the quarry, n = 19), upland breaks prairie (shallow rocky soil directly above the break of the hill (n = 50), lowland breaks prairie (steep-sloped shallow soil below the break of the hill, n = 105), and lowland prairie (relatively flat deep soil areas below the slope of the hill, n = 84). As this pasture was grazed by cattle, dung was scattered over the site; however, no dead wood other than the shelters was present. In July 1985, one inverted V-shaped trap shelter (26 cm long; untreated lumber ca. 4 cm thick) was placed directly on the ground at each of 480 trap stations (15-m spacing) on the 10.8-ha study site. Reticulitermes were observed by the first autumn but no records were made of attacked shelters until June 1989. These 1989 records, therefore, are a summation of termite activity during the four-year study period. In addition to presence of termite damage, shelters with heavy termite damage (a subjective category for damage that was sufficient to reduce the structural integrity of the shelter) were noted. Wood near the bases of many V-shaped shelters noted as having experienced heavy damage was falling apart by summer 1989. On 12-13 July 1989, shelters were surveyed for the presence of termites with a sample of termites collected from 21 shelters. All were Reticulitermes but identification to species was not possible as alates were not present.

MICROGEOGRAPHIC VARIATION IN MITOCHONDRIAL DNA OF MEADOW VOLES (MICROTUS PENNSYLVANICUS) IN RELATION TO POPULATION DENSITY.

We examined mitochondrial-DNA (mtDNA) sequence heterogeneity on four adjacent trapping grids in an island population of meadow voles (Microtus pennsylvanicus) at two different population densities. Four restriction endonucleases revealed 20 different mtDNA composite phenotypes in samples totaling 198 meadow voles. There were significant heterogeneities in the distribution of four common mtDNA composite phenotypes among the four trapping grids, suggesting that there is population subdivision on a fine scale. Genetic distances between grids, mtDNA diversity within grids, and GST also varied during the study period. We found a decrease in genetic distance and an increase in diversity when the population density was high and vice versa when the population density was low. When population density was high, the coefficient of gene differentiation was smaller than the same coefficient observed when the population density was low. These changes in population subdivision and diversity are consistent with theoretical expectations of population structure in which effective female population size and dispersal are the critical variables. The data also support the hypothesis of maintenance of mtDNA diversity by population subdivision, rapid population growth rate, and dispersal.