Trapping Sessions Research Articles

Differences in dung beetle activity at western gorilla defecation sites in south-east Cameroon: implications for establishment of Uapaca spp. seedlings

Abstract:For endozoochorous seed dispersal systems, the extant dung beetle assemblage at seed deposition sites may influence site suitability as burial activity may change the probability that seeds germinate and seedlings establish. This study tested if the different conditions of the two main seed-deposition habitats of a western lowland gorilla population of south-east Cameroon (sleeping sites and old secondary forest) influenced dung beetle assemblages and consequently the seed relocation patterns. In March 2012, in both habitats, burial patterns (proportion and depth) were described in eight stations based on two 300-g experimental faeces with known number of Uapaca spp. seeds (N = 75) left for 48 h, and beetle assemblages were described based on one 48h-dung-baited pitfall trapping session in five of these stations. To assess the impact of burial pattern on seedling emergence, Uapaca seedling emergence trials were performed in a nursery (75 seeds per depth treatment). Assemblage at sleeping sites had a higher species richness (non-significant) and was significantly more abundant than in old secondary forests. Conversely, significantly more seeds were buried in old secondary forests than sleeping sites and at significantly greater depths (mean: 14.9 cm vs. 8.7 cm). As trials suggested that burial depth ≥7 cm prevented Uapaca seedling emergence, dung beetles are assumed to induce seed loss more strongly in old secondary forests than sleeping sites (20.5% vs. 6.7% of initial seed crop). The demonstration that dung beetles may exert a negative influence on seed fate overall, and that the degree to which this occurs may vary depending on habitat, highlights the complexity in determining the suitability of deposition sites for recruitment.

Factors that influence trap success of sandhill dunnarts (Sminthopsis psammophila) and other small mammals in Triodia dunefields of South Australia

Optimised detection and sensitivity of fauna-monitoring programs is essential for the adaptive management of threatened species. We describe the influence of trap type, trapping duration and timing on the detection rates of small vertebrates, in particular the nationally endangered sandhill dunnart (Sminthopsis psammophila) in its two primary populations in South Australia. A total of 118 and 155 sandhill dunnarts were captured from the Middleback and Yellabinna regions, respectively, from five trapping sessions between 2008 and 2012. Wide deep pitfall traps (225 mm diameter × 600–700 mm deep) captured significantly more adult sandhill dunnarts than shorter, narrower pitfalls (150 mm diameter × 500 mm deep) or Elliott traps. Deep pitfall traps also captured significantly more hopping mice (Notomys mitchellii) but smaller mammal species were equally trapable in deep or short pitfall traps. Capture rates declined through successive nights of trapping. Capture rates of sandhill dunnarts were greatest in one study region when the moon illumination was less than 40% compared with fuller moon phases but were not affected by moon illumination in the other study region. The results suggest that higher capture rates of sandhill dunnarts will be achieved when using wide, deep pitfall traps on dark nights during the first two nights of trapping. Trapping in summer detected more juvenile sandhill dunnarts than trapping in winter.

Efficiency of small mammal trapping in an Atlantic Forest fragmented landscape: the effects of trap type and position, seasonality and habitat.

Trapping methods can strongly influence the sampling of mammal communities. This study compared the efficiency of the capture of small mammals in Sherman traps in two positions (at ground level and in trees) and pitfall traps in a fragmented landscape. Trapping sessions were carried out between October 2008 and October 2009 at two fragments (8 and 17 ha), an agroforest corridor between them, and the adjacent pasture. A total effort of 4622 trap-nights resulted in 155 captures of 137 individuals from six species. Pitfalls had greater success (4.03%), followed by Shermans on the ground (2.98%) and on trees (2.37%; χ2 = 6.50, p = 0.04). Five species were caught in Sherman ground traps, four in pitfalls and just two on trees. There was no difference among trap types for marsupials (χ2 = 4.75; p = 0.09), while for rodents, pitfalls were more efficient than Shermans on the ground (Fisher's exact test, p = 0.02). As a result, the efficiency of each trap type differed among habitats, due to differences in their species composition. Pitfalls were more efficient in the rainy season (Fisher's exact test, p <0.0001) while Shermans on trees were more efficient in the dry season (Fisher's exact test, p = 0.009). There was no difference between seasons for Shermans on the ground (Fisher's exact test, p = 0.76). Considering the results found, we recommend that future studies of forest mammal communities, particularly those designed to test the effects of forest fragmentation, include combinations of different trap types.

The effects of agricultural management on the reproductive activity of female rodents in Argentina

The aim of this study was to test if female rodents in border habitats of organic farms have higher reproductive activity than those of conventional farms in south-east Córdoba province, Argentina. The study was conducted in field borders of organic and conventional farms in 2012 and 2013 during the summer months, the time of the year when reproductive activity is more likely. We sampled field borders through a CMR trapping session and recorded vegetation cover, plant litter, vegetation volume, bare ground cover and land use of the field on both sides of the border (crop/crop or crop/pasture). We recorded the number of reproductive females and the rate of postpartum estrus. Green vegetation cover was higher in organic borders whereas plant litter was higher in borders of conventional farms. We used Generalized Linear Mixed Models (GLMM) to determine the factors that influence the number of reproductive females in borders of organic and conventional farms. The number of reproductive females was mainly determined by agriculture management and field type. There were more reproductive females in organic than in conventional borders, and borders associated with crop fields at both sides supported the highest number of reproductive females. The rate of postpartum estrus was higher in organic than in conventional borders. Our results showed that in border habitats of farms under organic management reproductive activity of female rodents was higher than in borders of conventional farms. Organic farm borders may provide high quality habitats that provide resources for reproduction and persistence of rodent populations.

Rat Control in New Caledonian “Mainland Island” Rainforests: Will the Game be Worth the Candle?

Author(s): Duron, Quiterie; Bourguet, Edouard; Franquet, Romain; Folger, Djaek; Teimpouene, Gabriel; Wanguene, Maurice; Cassan, Jean-Jerome; Rigault, Frederic; De Meringo, Helene; Millon, Alexandre; Vidal, Eric | Abstract: Due to its unique biodiversity and extreme endemism rates, New Caledonia archipelago is listed as one of Earth’s 35 biodiversity hotspots. New Caledonian biota is now threatened by invasive species, with introduced rats considered to be particularly damaging. At the initiative of local institutions and NGOs, an innovative scientific experiment has been launched to quantify the Response of Forest Ecosystems to Rodent and Cat Control (REFCOR) and to test the relevance of such control at a large spatial scale (200 ha) on a dense evergreen rainforest (Mont Panie Wilderness Nature Reserve). Rat control will begin mid-2014 with a short toxin knockdown, and will thereafter involve intensive trapping sessions over the next 6 years, together with biodiversity monitoring and experiments. Rat impact studies initiated in early 2013 also aim to identify possible biodiversity indicators that could be used for a rapid assessment of rat control efficiency and effects. One of the major impacts of invasive rats is the disruption caused to plant and bird reproduction processes, placing them at high risk. Pre-and post-control experiments include the assessment of palm fruit consumption rates and of predation risk to artificial bird nests. Initial surveys of both rat populations and palm fruits (2 species), as well as artificial bird nest predation experiments, were conducted in 2013. Rat abundance was high, fluctuating among study areas and seasons, with more individual reproducers in December than in May. Fruit predation was high for one of the two species, in line with the rat abundance pattern. Surprisingly, artificial bird nest predation by rats was far lower than expected. These first results corroborate the influence of rats on some taxa. Monitoring and experiments will be repeated after and throughout rat control. This “before-after-control-impact” project, conducted in close collaboration with local stakeholders (Dayu Biik NGO), offers a unique opportunity to evaluate 1) the feasibility of controlling rat populations in the New Caledonian rainforest by trapping as an alternative to long-term poisoning, and 2) the benefits of rat control for native biodiversity and rainforest ecosystem functioning.

Separating mortality and emigration: modelling space use, dispersal and survival with robust‐design spatial capture–recapture data

Summary Capture–recapture (CR) techniques are commonly used to gain information about population dynamics, demography and life‐history traits of populations. However, traditional CR models cannot separate mortality from emigration. Recently developed spatial–capture–recapture (SCR) models explicitly incorporate spatial information into traditional CR models, thus allowing for individuals' movements to be modelled explicitly. In this paper, we extend SCR models using robust‐design data to allow for both processes in which individuals can disappear from the population, mortality and dispersal, to be estimated separately. We formulate a general robust‐design spatial capture–recapture (RD‐SCR) model, explore the properties of the model in a simulation study and compare the results to a Cormack–Jolly–Seber model and a non‐spatial robust‐design model with temporary emigration. In the case study, we fit several versions of the general model to data on field voles (Microtus agrestis) and compare the results with those from the non‐spatial models fitted to the same data. We also evaluate assumptions of the fitted models with a series of simulation‐based posterior predictive goodness‐of‐fit checks that are applicable to the SCR models in general and the RD‐SCR model in particular. The simulation results show that the model preforms well under a wide range of dispersal distances. Our model outperforms the traditional CR models in terms of both accuracy and precision for survival. The case study showed that adult females have an c. 3·5 times higher mortality rate than adult males. Males have larger home ranges and disperse longer distances than females, but both males and females mostly move their activity centres within their previous home range between trapping sessions at 3‐week intervals. Our RD‐SCR model has several advantages compared to other approaches to estimate ‘true’ survival instead of only ‘apparent’ survival. Additionally, the model extracts information about space use and dispersal distributions that are relevant for behavioural studies as well as studies of life‐history variation, population dynamics and management. The model can be widely applied due to the flexible framework, and other variations of the model could easily be implemented.

Saphenous venipuncture for field collection of blood from least chipmunks

ABSTRACTDuring a study of least chipmunks (Tamias minimus), we successfully collected whole blood from 166 individuals via venipuncture of the saphenous vein. This method allowed us to collect quantities of blood suitable for various blood analyses and resulted in minimal and localized tissue damage from the puncture. Recapture rate within trapping sessions during the year we used saphenous venipuncture (2010) was similar to that in years when we did not collect blood (2006, 2008, 2009, and 2011). In addition, recaptured individuals showed full wound healing within 24 hr of blood collection. Based on our experience, we recommend saphenous venipuncture for field research over other methods commonly used for collection from small mammals, including bleeding from the retro‐orbital sinus and tail clipping, because of reduced discomfort and injury to the animal, rapid healing at the puncture site, and the limited influence on recapture and survival. © 2013 The Wildlife Society.

Short-term welfare implications of capture-mark-recapture trapping of medium-sized mammals: the brushtail possum (Trichosurus vulpecula) as a case study

AbstractCapture-mark-recapture (CMR) repeated at intervals is a commonly used method of population estimation of mammals. Most guidelines for the use of wild mammals recommend adequate measures to ensure a captured animal has food and water available, as needed, until it is released. Small mammals are often highlighted as needing special care, but recommendations are either less clear or absent for medium- and large-sized mammals. We therefore examined the short-term welfare implications of CMR trapping of medium-sized mammals, using the marsupial, brushtail possum (Trichosurus vulpecula) as a case study. Possums were caught in cage traps baited withcirca30 g of food and set for three consecutive days at monthly intervals. Timing devices on the traps measured when traps were sprung. Possums were confined in traps for, on average, 89% of each night they were trapped, plus a further 2-6 h between sunrise and the actual time of release from the traps. They lost 3-8% of their bodyweight on average, depending on the number of captures in a trapping session. A recently developed framework for humaneness assessment, based on five welfare domains, gave an overall welfare impact of mild-moderate for cage trapping of possums. The short-term solutions to these welfare impacts would be, at a minimum, to provide trapped possums with adequate additional food and water, and minimise their time spent in the traps. Guidelines for the use of wild animals in research and management could also be more prescriptive regarding the provision of food and water in studies of medium-sized mammals that involve repeated capture.

Habitat manipulation in lowland rice-coconut cropping systems of the Philippines-an effective rodent pest management strategy?

Reduction of vegetation height is recommended as a management strategy for controlling rodent pests of rice in South-east Asia, but there are limited field data to assess its effectiveness. The breeding biology of the main pest species of rodent in the Philippines, Rattus tanezumi, suggests that habitat manipulation in irrigated rice-coconut cropping systems may be an effective strategy to limit the quality and availability of their nesting habitat. The authors imposed a replicated manipulation of vegetation cover in adjacent coconut groves during a single rice-cropping season, and added artificial nest sites to facilitate capture and culling of young. Three trapping sessions in four rice fields (two treatments, two controls) adjacent to coconut groves led to the capture of 176 R. tanezumi, 12 Rattus exulans and seven Chrotomys mindorensis individuals. There was no significant difference in overall abundance between crop stages or between treatments, and there was no treatment effect on damage to tillers or rice yield. Only two R. tanezumi were caught at the artificial nest sites. Habitat manipulation to reduce the quality of R. tanezumi nesting habitat adjacent to rice fields is not effective as a lone rodent management tool in rice-coconut cropping systems.

Wheat fields as an ecological trap for reptiles in a semiarid agroecosystem

Intensive agricultural activity over large areas on earth, which is necessary to meet the increasing demand of a growing human population, may lead to biodiversity loss. This loss may be mitigated by keeping natural and semi-natural patches within agricultural fields to allow the maintenance of biological diversity (‘Wildlife Friendly Agriculture’). We conducted our study in an agroecosystem comprised of small isolated patches nested within agricultural fields. We trapped reptiles in 13 sampling sites, each of which included arrays of pitfall traps in a natural patch, in the adjacent wheat field and at the patch-field edge. We conducted six trapping sessions in the spring – four times before, once immediately after and once a week after the wheat harvest. Prior to the harvest, we found an intensive movement of Trachylepis vittata, the most common reptile in our study, from the semi-natural patches into the fields, but negligible movement in the opposite direction. This pre-harvest directional movement corresponded with higher abundance of prey (i.e., arthropods) in the wheat field compared to the natural patches in early spring. The individuals that moved into the fields were adults of better body condition than those remaining in the patch, suggesting that the motivation for movement was habitat preference by individuals with high prospective fitness rather than the exclusion of subordinates. The population of T. vittata in the wheat fields and movement across habitats dropped to zero during and after the harvest. Our results provide strong evidence that the agricultural fields serve as an ecological trap to organisms inhabiting nearby natural habitats. We suggest that plans for Wildlife-Friendly Agriculture for biodiversity conservation should consider also potential negative effects, such as the ecological trap effect.

The role of behavioural heterogeneity on infection patterns: implications for pathogen transmission

Animals infected with pathogens often differ in behaviour from their uninfected counterparts, and these differences may be key to understanding zoonotic pathogen transmission. To explore behavioural heterogeneity and its role in pathogen transmission, we studied deer mice, Peromyscus maniculatus, under field conditions. Deer mice are the natural host of Sin Nombre virus (SNV), a zoonotic pathogen with high human mortality. We live-trapped mice in May, July and September of 2009 and 2010, marked captures with passive integrated transponder (PIT) tags, recorded physical characteristics and collected blood samples for SNV analysis. For 4 nights after each trapping session, we observed behaviour with a novel surveillance system of nine camera stations, each consisting of a foraging tray, infrared camera, PIT antenna and data logger. We found that deer mice infected with SNV (30.0%) engaged more frequently in behaviours that increased the probability of intraspecific encounters and SNV transmission than did uninfected deer mice. When deer mice were categorized as bold (31.7%) or shy (68.3%) based on these behaviours, bold behaviour was predictive of positive SNV status. Bold deer mice were three times more likely to be infected with SNV than were shy deer mice. These results suggest that a small percentage of bold individuals are responsible for a majority of SNV transmission events, and that behavioural phenotype is an important consideration in transmission dynamics of zoonotic diseases.

Effects of Repeated Captures on Body Mass and Survival of Dusky-Footed Woodrats in a California Oak Woodland

Abstract Trapping sessions consisting of repeated captures are routinely used to assess demography, social organization, and habitat associations of small mammals. Some capture-recapture analyses require a high number of trapping occasions for precise estimates, but repeatedly capturing an animal may have adverse effects on individuals and populations. During 2002–2006, we examined patterns of capture, changes in body mass, and longer-term survival in a population of dusky-footed woodrats (Neotoma fuscipes). During 10 trapping sessions of 3 nights each, we captured 1,824 woodrats 4,705 times. Captures per individual averaged 1.6/trapping session. Nearly all woodrats (91%) lost mass at a rate of 3.5%/capture. Mass loss was cumulative over consecutive days, averaging ca. 3.5% of body mass after the second capture and 6.8% after the third capture. Woodrats lost slightly more mass during trapping sessions in the fall than during sessions in the spring. Percentage of change in mass was not associated with age ...

A Coupled Hidden Markov Model for Disease Interactions

To investigate interactions between parasite species in a host, a population of field voles was studied longitudinally, with presence or absence of six different parasites measured repeatedly. Although trapping sessions were regular, a different set of voles was caught at each session, leading to incomplete profiles for all subjects. We use a discrete time hidden Markov model for each disease with transition probabilities dependent on covariates via a set of logistic regressions. For each disease the hidden states for each of the other diseases at a given time point form part of the covariate set for the Markov transition probabilities from that time point. This allows us to gauge the influence of each parasite species on the transition probabilities for each of the other parasite species. Inference is performed via a Gibbs sampler, which cycles through each of the diseases, first using an adaptive Metropolis–Hastings step to sample from the conditional posterior of the covariate parameters for that particular disease given the hidden states for all other diseases and then sampling from the hidden states for that disease given the parameters. We find evidence for interactions between several pairs of parasites and of an acquired immune response for two of the parasites.

A methodology for long-term population monitoring of the endangered key largo cotton mouse

The Key Largo cotton mouse (Peromyscus gossypinus allapaticola) was federally listed as Endangered in 1984 due to habitat loss and subsequent population decline, but because of infrequent monitoring, the extent of decline and long-term population trends are unknown. We modeled population abundance under a variety of trapping scenarios to develop a monitoring protocol that would provide accurate population estimates and could be conducted more frequently under current personnel and budget constraints. We captured cotton mice on 33 trapping grids in Key Largo, Florida, USA, during 3 trapping sessions (1 Mar–11 May, 4 Jul–7 Sep, and 29 Oct–31 Dec) in 2007. We compared demographic parameter estimates from subsets of trapping grids with estimates from all grids to identify a subset of grids that would produce population estimates within 10% and remain within the 95% confidence intervals of estimates using all grids when both methods were extrapolated to total available habitat. There were insufficient captures in session 1 to produce a reliable population estimate. We found that 13 and 12 trapping grids, respectively, produced abundance estimates meeting our criteria in sessions 2 and 3. We conclude that the subset of 12 grids trapped during November and December will allow a 64% reduction in number of trapping grids necessary to provide a reliable population estimate. Employed annually, our recommended trapping protocol provides state and federal agencies an efficient method for monitoring trends in the Key Largo cotton mouse population. © 2013 The Wildlife Society.

Relative abundance of the central rock-rat, the desert mouse and the fat-tailed pseudantechinus at Ormiston Gorge in the West MacDonnell Ranges National Park, Northern Territory

This study examines the relative abundance of two species of sympatric rodent, the desert mouse (Pseudomys desertor) and the central rock-rat (Zyzomys pedunculatus), and a sympatric dasyurid (Pseudantechinus macdonnellensis) in relation to rainfall in the West Macdonnell Ranges National Park, Northern Territory, over a 6-year period. Seventeen trapping sessions were conducted between July 2000 and September 2006. All three species showed spikes in abundance during 2001 and 2002, which were very wet years, and then declined as rainfall diminished. Z. pedunculatus was not trapped at the sites beyond June 2002 while P. desertor was not trapped beyond September 2002. P. macdonnellensis was trapped in low numbers between September 2002 and February 2005 but was not trapped subsequently. Rainfall and the abundance of all three mammal species were clearly correlated. However, the patterns of abundance were subtly different. Z. pedunculatus exhibited three distinct peaks in abundance during the study (July 2000, April 2001 and March 2002), P. desertor exhibited two distinct peaks (July 2001 and June 2002) while. P. macdonnellensis exhibited only one peak in abundance (March 2002). The results of this study provide more evidence that populations of both arid Australian rodents and some dasyurids are influenced by rainfall. The study also provides some insights into the population ecology of the poorly known and threatened central rock-rat.

Comparison of different trapping methods for surveillance of mosquito vectors of West Nile virus in Rhône Delta, France

Five trapping methods were compared for monitoring potential vectors of the West Nile virus in four areas in the Camargue Plain of France: carbon dioxide traps, bird-baited traps, gravid traps, resting boxes, and human landing catches. A total of 73,721 specimens, representing 14 species, was trapped in 2006. Results showed significant differences in species and abundance between the type of traps. Many more specimens were collected using CO(2) traps than any other method, with an average of 212 specimens per night per trap (p<0.05). Culex pipiens was the most abundant species collected (36.8% of total with CO(2) traps), followed by Aedes caspius (22.7%), Anopheles hyrcanus (18.3%), Culex modestus (18.3%), and Aedes detritus (3.2%). Bird-baited traps captured only eight specimens per night per trap on average, mainly Cx. pipiens (89.9%). The species collected and their abundance are influenced by the trap location, at ground or canopy level. Culex pipiens was twice as abundant in the canopy as on the ground, whereas it was the opposite for Ae. caspius, An. hyrcanus, and Ae. detritus. Culex modestus was equally abundant at both levels. Resting boxes and gravid traps were much less efficient, capturing around 0.3 specimens per night per trap. Results are discussed in relation to West Nile virus surveillance.

Edge effects on small mammal assemblages in Sri Lankan rainforests

This project was carried out with the objective of investigating edge effects on species richness and abundance of small mammals in rainforests of Sri Lanka. Core and edge habitats of twelve rainforests were live-trapped for five consecutive nights each, during 2006 and 2007. Habitat assessments were also carried out to ascertain differences in microhabitat features between core and edge habitats. A total of nine species (seven rodents and two shrews) were captured during the survey (two species were from additional trapping sessions). Species richness was marginally higher in core areas (six species) than at forest edges (five species). No marked differ ences were also evident in total abundance with 91 individuals being captured from core habitats and 89 from forest edges. With regard to habitat utilization patterns of the small mammals, of the four endemics, Mus mayori and Crocidura miya used both core and edge habitats whilstFunambulus layardi and Suncus zeylanicus were confined to core areas of the forest. Of the non-endemics, F. sublineatus was confined to the forest, Vandeleuria oleracea and M.booduga used only edge habitats and F. palmarum and Rattus ratttus were found in both core and edge habitats. Interestingly, a remarkable disparity was evident between the abundance of the endemics and non-endemics. The number of endemics was much higher in core areas (55 individuals) than in forest edges (34 individuals). A reverse trend was noted for the non-endemics. The microhabitat conditions within the forest were different to that in forest edges. Core areas were generally characterized by greater numbers of large trees and seedlings, higher humidity and cooler temperatures. These findings indicate that although rain forest fragmenta tion and the resultant changes at forest edges do not have a great impact on the overall diversity of small mammals and the endemics would suffer greater adverse consequences than the non-endemics.

Edge effects on small mammal assemblages in Sri Lankan rainforests

This project was carried out with the objective of investigating edge effects on species richness and abundance of small mammals in rainforests of Sri Lanka. Core and edge habitats of twelve rainforests were live-trapped for five consecutive nights each, during 2006 and 2007. Habitat assessments were also carried out to ascertain differences in microhabitat features between core and edge habitats. A total of nine species (seven rodents and two shrews) were captured during the survey (two species were from additional trapping sessions). Species richness was marginally higher in core areas (six species) than at forest edges (five species). No marked differ ences were also evident in total abundance with 91 individuals being captured from core habitats and 89 from forest edges. With regard to habitat utilization patterns of the small mammals, of the four endemics, Mus mayori and Crocidura miya used both core and edge habitats whilstFunambulus layardi and Suncus zeylanicus were confined to core areas of the forest. Of the non-endemics, F. sublineatus was confined to the forest, Vandeleuria oleracea and M.booduga used only edge habitats and F. palmarum and Rattus ratttus were found in both core and edge habitats. Interestingly, a remarkable disparity was evident between the abundance of the endemics and non-endemics. The number of endemics was much higher in core areas (55 individuals) than in forest edges (34 individuals). A reverse trend was noted for the non-endemics. The microhabitat conditions within the forest were different to that in forest edges. Core areas were generally characterized by greater numbers of large trees and seedlings, higher humidity and cooler temperatures. These findings indicate that although rain forest fragmenta tion and the resultant changes at forest edges do not have a great impact on the overall diversity of small mammals and the endemics would suffer greater adverse consequences than the non-endemics.

Behavioural responses of brushtail possums to live trapping and implications for trap-catch correction

Context The behavioural response of animals to repeated trapping has implications for correction of population and monitoring indices that use catch per unit effort. Failure to account for sprung traps introduces biases into estimates of relative abundance. The time when animals get caught in live traps is often ignored, but it can provide important information about temporal movement patterns relevant to this issue. Aims We assessed changes in the behaviour of brushtail possums (Trichosurus vulpecula), a nocturnal marsupial, in response to repeated trapping and evaluated the potential benefit of correcting a commonly used index of abundance by using time-of-capture information. Methods Possums were live-trapped for three nights each month over a 20-month period in baited cage traps in a 6-ha area of native lowland forest in the southern North Island, New Zealand. Trapped possums were individually identified on first capture. Timing devices were attached to the traps to measure how long after sunset traps were sprung and how that time related to the duration of the trap-night (sunset to sunrise). Key results Possums were trapped, on average, ~1.25 h after sunset. Traps triggered other than by possums were sprung on average 1–2 h later. Possums caught on the first night of a trapping session were caught significantly earlier than those caught on subsequent nights. Previous capture influenced the time of subsequent capture in a trapping session in complex ways, and recapture times were generally earlier than times of first capture. Possums were captured, on average, after 11% of the duration of a trap-night and traps were triggered by animals other than possums, on average, after 22% of the duration of a trap-night. Conclusions The data on time of capture of possums and triggering of sprung traps suggested a need to alter the commonly used correction factor for population indices for possums, because, on average, traps were sprung for significantly more of each trapping interval (i.e. trap-night) than the half a trap-night assumed in the correction factor. Implications Better understanding of possum foraging behaviour is a key to more effective control using traps. In that context, more research is needed to understand the reasons for individual differences in trappability. Although it is theoretically desirable to account for sprung traps when trapping is used to index populations, to reduce biases in estimates of relative abundance, correction of the standardised residual trap-catch index for possums is probably unimportant in practical terms, because most possum control reduces numbers to levels (2–5% trap catch) at which correction of the index is unimportant. The principal exception to this is likely to be when there is a high level of non-target interference from rodents.

IMPACT OF PUUMALA VIRUS INFECTION ON MATURATION AND SURVIVAL IN BANK VOLES: A CAPTURE-MARK-RECAPTURE ANALYSIS

Many zoonotic diseases are caused by rodent-borne viruses. Major fluctuations in the transmission of these viruses have been related to large changes in reservoir host population numbers due to external factors. However, the impact of the pathogen itself on the demography of its reservoir host is often overlooked. We investigated the impact of Puumala virus (PUUV) on survival and reproductive maturation probability of its reservoir host, the bank vole (Myodes glareolus). Three years (2004-06) of data from nine independent sites in southern Belgium were collected and analyzed with a capture-mark-recapture (CMR) method that includes statistical correction for the variation in capture probability of voles. A multistate model based on four states of reproductive activity and PUUV immunoglobulin G (IgG) antibody status was used to estimate survival and probability of transition from one reproductive or infection state to another. Although survival estimates for reproductively active voles were similar between infected and noninfected individuals, PUUV infection in reproductively inactive voles decreased mean monthly survival by 14%. PUUV infection was associated with a threefold increase in the probability of reproductive maturation in bank voles. Moreover, the probability of PUUV IgG seroconversion was three times higher for reproductively active voles compared to reproductively inactive voles. Our model indicates that PUUV infection may alter bank vole population dynamics by affecting both survival and maturation in its host. Additional studies, using CMR methodology with shorter time intervals between trapping sessions and possibly a longer duration, are needed to confirm these findings.