A technique for quantitative estimation of small mammals traversing water obstacles

A new method for quantitative study of small mammals swimming across water obstacles was developed. A line of 25 traps was installed on either poles or boards (“rafts”) with anchors at a distance of 20–25 m from the bank and with 10-m distances between the items. The study was performed upstream along the Ilych River in August 2013. A total of 300 trap/day were accumulated. Twenty-four small mammal individuals of 8 species were captured. Their relative abundance was estimated as the number of individuals per 100 trap/day. It was found experimentally that floating poles neither repel nor attract animals. When an individual accidentally finds a floating pole, it climbs up and explores it for some time. The number of animals per total length of rafts per time unit can be suggested as an index of intensiveness of migration across a water obstacle. In the area studied, the number of small mammals of various species crossing the river was estimated at 26.7 individuals per 1 km/day. A length of 5 m for floating poles/boards and installation of two traps at the ends of an item is suggested to be used.     

A new technique using metal tags to track small seeds over short distances

Myrmecochory (seed dispersal by ants) is an evolutionarily and ecologically common mutualism. Since the first study of the phenomenon, ecologists have sought to develop techniques to track ant-dispersed seeds. Often, thick leaf litter and the potential burial of seeds by ants make tracking of seeds difficult. Here we describe a seed-tracking technique for small seeds, which uses magnetic tags, developed for mark–recapture studies of fish, to track seeds after dispersal into the ant nest in temperate deciduous forests. We discuss our use of the technique as well as suggestions for improvement and other possible applications of the technique.     

Movement and spatial organization of small mammals following vertebrate predator exclusion

Predation directly changes the demographics of prey, generally through a numerical decrease. An indirect effect of predators is alteration of movements and spatial patterns of prey. The relationship between these direct and indirect effects can be tested by excluding predators. Home range size of white-footed mice (Peromyscus leucopus) decreased and home range overlaps increased in the absence of predators. Home range size and overlaps of meadow voles (Microtus pennsylvanicus) did not change despite an increase in vole density. P. leucopus had significantly lower interspecific home range overlaps with M. pennsylvanicus than intraspecific overlaps. The changes in P. leucopus spatial behavior may be an indirect effect of predator exclusion resulting from the increase in M. pennsylvanicus densities.     

Habitat selection by two species of small mammals in the Atlantic Forest,Brazil: Comparing results from live trapping and spool-and-line tracking

Habitat selection by small mammals is usually evaluated using data from live trapping, which provides little information about the movements of individuals. Few studies used movement data or compared the results of different sampling methods to study habitat selection by these animals. We evaluated habitat selection by the rodent Nectomys squamipes and the marsupial Micoureus paraguayanus in the Atlantic Forest of Brazil using the spool-and-line technique. We also determined if percentage of captures reflected the amount of movements in each habitat. Habitat selection was determined comparing use and availability of five habitat types at two spatial scales (movement paths and movement areas) using compositional analysis, which allowed ranking of habitats according to their relative use by animals. The use of available habitat types was non-random for both species at both spatial scales. The two species had contrasting habitat affinities directly related to their particular habits, with N. squamipes using predominantly the stream habitat, and M. paraguayanus using mainly the restinga forest habitat. Patterns of habitat selection were similar at both spatial scales probably due to the small size of movement areas, which may not represent habitat use at a broader scale. For both species, live trapping and movement data provided the same ranking in habitat use, demonstrating that simple capture indices may be used to study habitat selection by these species across different habitat types.     

Movement of the epiglottis in mammals

In contrast to adult humans, the epiglottis of other mammals and infant humans is situated close to the soft palate. It has been argued that this posture is maintained during swallowing, with food passing laterally around an intact airway. To test this supposition, the movement of the epiglottis in two contrasting mammalian species, pigs and ferrets, was studied by placing radiopaque markers on the epiglottis and soft palate. Swallowing was observed with videofluoroscopy while the animals were feeding on hard and soft foods, liquids, and food mixed with barium sulfate. Analysis of the images showed that bolus formation and downward movement of the epiglottis away from the soft palate were unvarying phenomena in both animals for all tested foods. The duration of the epiglottic movement was approximately 0.3 s for liquids and slightly longer for solids. Because swallowing never occurred past an upright epiglottis, the results of this study do not support the hypothesis that adult animals maintain a patent airway during swallowing. Instead, the epiglottis in nonhuman mammals downfolds similarly to that of adult humans during swallowing. © 1996 Wiley-Liss, Inc.     

A technique for using hair tubes beneath the snowpack to detect winter-active small mammals in the subnivean space

The study of winter-active small mammals beneath the snowpack has proved challenging for researchers because of the relative inaccessibility. We present a technique using hair tubes that permits the detection of small mammals active in the subnivean space. Hair tubes are cylindrical or funnel-shaped structures containing suitable bait and an adhesive surface that harvests hairs from small mammals as they attempt to reach the bait. Hair tubes eliminate many of the difficulties often associated with live trapping and permit the expansion of systematic sampling to larger scales than allowed by conventional live-trapping methods. The technique was used successfully to detect five small mammal species in the subnivean space in Kosciuszko National Park (KNP) in southeastern Australia. These included the common bush-rat, Rattus fuscipes; the dusky and agile antechinus, Antechinus swainsonii and A. agilis; the broad-toothed rat, Mastacomys fuscus; and the mountain pygmy possum, Burramys parvus. Although hair tubes have a number of limitations, such as not providing a measure of abundance or allowing the identification of individual animals, we believe that these limitations are balanced by the fact that the technique can be used at any spatial scale. Hair tubes are particularly suited to studies of animal distribution at the landscape-scale, because many hair tubes can be deployed and dispersed over large areas, and monitored on a regular basis by a small team of researchers. The technique also makes use of readily available, low-cost materials and could be easily adapted to a range of conditions and different target species.     

Modeling the eradication of invasive mammals using the sterile male technique

Large vertebrates, like the domestic goat (Capra hircus), have been transported all over the world and are an ecological disaster to numerous island and mainland ecosystems. Eradication measures for such species are generally centered on lethal methods of removing individuals, an increasingly difficult process as populations become smaller and individual animals become much more difficult to detect. In addition, methods of lethal removal are becoming less desirable in the public eye, prompting the necessity to explore alternatives. Here we investigate the use of the sterile males technique as an effective strategy in the eradication of large mammals. The results of our simulations suggest that the use of sterile males as a single strategy would only be an effective measure to eradicate relatively small (no more than 100 individuals) isolated feral vertebrate populations. However, our results indicate that the technique could be employed as a successful and potentially cost-effective end-point complement to lethal control and/or as a preventative measure against re-invasion.     

Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on Borneo

1. Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2. We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13,525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3. Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4. Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features.     

A technique for the combination of clearing, staining, and injecting small mammals.

A combined method for clearing soft tissues, staining cartilage and bone, and injecting the vascular system of small mammals was developed using Mus musculus (house mouse). Mammalian muscle tissue remains milky or even opaque after "clearing" by previous techniques due to the relatively high content of intramuscular fat. A method employing chloroform-ethanol successfully renders soft tissues of mammalian specimens translucent without damaging or bleeding color from the latex injected in the circulatory system. Resulting specimens yield an excellent view of the skeletal system and the injected vascular system without obstruction by opaque tissues or disruption by physical removal of connective tissue.     

Quantifying torpor in small mammals non-invasively using infrared thermocouples

Measurements of torpor use are pivotal for many research areas concerning the thermal biology of endotherms. Here, I used infrared thermocouples to non-invasively examine torpor patterns in the small marsupial fat-tailed dunnart (Sminthopsis crassicaudata). Sensors were installed inside the nesting chambers to continuously monitor fur temperature in undisturbed animals. Firstly, to verify the measurements, fur temperature was monitored simultaneously with body temperature using internal radio transmitters (n=6). Secondly, I conducted a food restriction study to demonstrate the reliability of the method within a physiological experiment (n=8). Based on the correspondence of simultaneously measured fur and body temperature during torpor bouts, I was able to confirm that infrared thermocouples provide reliable temporal information on torpor patterns. Furthermore, torpor use was successfully monitored over a 20-day food restriction study. The method can easily be adapted to suit other small mammal or bird species and presents a useful, inexpensive approach for examining torpor patterns remotely and non-invasively in the laboratory.     

Respiratory measurements of unsedated small laboratory mammals using nonrebreathing valves

The respiratory frequency, tidal volume, minute volume, oxygen uptake and carbon dioxide output of unsedated hamsters, rats, guinea pigs and rabbits were measured to obtain comparative data and to evaluate the performance of those species as unsedated subjects. The animals were trained to remain stationary and breathe through nonrebreathing valves while expired gas was collected and respiratory frequency was monitored. Measurements of dogs also were conducted to obtained comparative data by similar methods. Hamsters were readily trained and performed reliably during repeated trials. Rats and guinea pigs were more difficult to train and performed erratically. The rabbits' performance was intermediate between that of hamsters and the other species. The back pressures caused by the small animal nonrebreathing valves at estimated peak flow rates were either similar to or less than those encountered by dogs. Measured respiratory values were compared to values predicted by published equations based on body weight. Data from this study generally reflected species differences related to body weight and metabolic rate similar to those predicted by the equations, but values from the four smaller species also may have reflected differences related to behavior.     

Separating effects of spatial location and microhabitat density on perceived predation risk in small mammals

acta ethologica - Prey animals must balance the benefits of foraging in a particular area with their risk of predation in that area and often prioritize indirect cues to predation risk over direct...     

Noninvasive estimation of body composition in small mammals: a comparison of conductive and morphometric techniques

Body fat stores may serve as an index of condition in mammals. Thus, techniques that measure fat content accurately are important for assessing the ecological correlates of condition in mammal populations. We compared the ability of two conductive techniques, bioelectrical impedance analysis (BIA) and total body electrical conductivity (TOBEC), to predict body composition with that of morphometric methods in three small mammal species: red squirrels (n=13), snowshoe hares (n=30), and yellow-bellied marmots (n=4). Animals were livetrapped in northern Idaho; BIA (all subjects) and TOBEC (squirrels only) measurements were taken following chemical immobilization in the field, and morphometric measurements were taken postmortem. Information provided by BIA and TOBEC failed to improve upon the predictive power of morphometric equations for total body water (TBW) and lean body mass (LBM) in squirrels and hares, which do not store substantial amounts of fat (<5% body mass comprised of fat). Although the same pattern held with respect to LBM in marmots, which accumulate substantial amounts of body fat (>10% body mass), a BIA-based model proved best at estimating TBW, suggesting that the usefulness of conductive techniques may be a function of fat deposition. However, regardless of the technique used to predict body composition, estimates of body fat furnished by our equations failed to approximate actual fat levels accurately in all three test species, probably because these techniques only provide indirect estimates of fat content. These results highlight the limitations inherent in contemporary methods of animal fat estimation and underscore the need for the development of direct and accurate measures of body fat in mammals.     

Interval estimation of the density of organisms using a serial-dilution experiment

The serial-dilution assay is a standard microbiological method for estimating the density of organisms in a solution. The commonly used interval-estimation procedures of Woodward and deMan are described and compared. A new method for the calculation of two-sided confidence intervals, which is superior to the standard procedures, is presented. The computations are illustrated for a decimal dilution assay with three samples at each of three dilutions.     

Microparasites of wild small mammals

Little is known of the biology of the majority of microparasites except for those of medical or veterinary importance. It is suggested that techniques already developed for identification and quantification of these important parasites should be modified as necessary and extended to the study of other microparasites. Isolation and maintenance of microparasites in laboratory-maintained hosts will improve these diagnostic techniques and will also allow investigation of the biology of the parasites under controlled conditions. The value of laboratory-based experiments as an adjunct to ecological studies is emphasized. Problems of interpretation are indicated.     

Mutagenicity testing and risk estimation with mammals

Mammalian test systems are currently used for mutagenicity screening. The necessity and the limitations of standardizing these methods are discussed for the dominant-lethal assay. In addition to the refinement of standard methods, the development of new systems in mammals is emphasized. One promising approach is the detection of presumed somatic mutations. Another new development takes advantage of electrophoretic methods for detecting induced structural alterations of gene products. Mammalian experiments will be essential for the assessment of risks from chemical mutagens. The development of standards for the controlled use of chemical mutagens should be guided by the experience accumulated in radiation genetics. Two methods, the measurement of specific-locus mutation rates in mice and the direct determination fo the phenotypic damage of dominant genes affecting the skeleton of mice, are recommended for the assessment of the hazard of chemical mutagens.     

Obtaining high-quality DNA from elusive small mammals using low-tech hair snares

Noninvasive sampling approaches are becoming increasingly important for enabling genetic studies of wildlife populations. While a number of methods have been described to noninvasively sample hair from carnivores and medium-sized mammals, they have largely remained untested in elusive small mammals. Here we describe a novel and inexpensive noninvasive hair snare targeted at an elusive small mammal, the American pika (Ochotona princeps). We explore the quality of the sample by assessing PCR amplification success of mitochondrial and nuclear DNA fragments across four commercially available DNA isolation kits and two different quantities of hair in a factorial design. Additionally, we determined the sex of the individual samples using PCR–RFLP of ZFX/ZFY loci. We found that our snare is effective in obtaining hair that yield DNA of sufficient quality and quantity to successfully amplify a range of mitochondrial and nuclear fragment sizes. Specifically, we found the greatest success in amplifying mitochondrial DNA, nuclear microsatellites and ZFX/ZFY loci using at least 25 hairs as starting material and the DNA IQ™ system. The hair snares thus provide a cost-effective and minimally intrusive approach to sample elusive or rare small mammals. We anticipate that this approach will be useful to obtain samples for molecular studies of the ecology, evolution and conservation of small, elusive mammals.