Suchergebnisse

The potential effects of predation risk on common brushtail possums were investigated in south-eastern Australian woodlands. Patterns of habitat use, foraging costs using giving-up density (GUD) experiments, and indices of body condition and reproductive success were examined at eight sites in two habitat types (eucalypt- or cypress-pine–dominated stands), within three areas of different red fox abundance (high, moderate and low fox density). In cypress-pine–dominated stands, possums travelled further on the ground, visited more feeding stations and had lower GUDs at feeders where foxes were removed than did possums in high-fox-density sites. In contrast, there was no effect of fox removal on the behaviour of possums in eucalypt-dominated stands. Fox removal also had no effect on indices of body condition and reproduction. Minor effects of microhabitat were detected with trackplot and GUD experiments, but, overall, the results suggest that habitat at the stand-level was more important. The non-lethal effects of foxes in different habitats may need to be taken into account when developing conservation strategies for native marsupials.

Context Seasonal and individual variation in predator selection for primary and alternative prey can affect predator–prey dynamics, which can further influence invasive-predator impacts on rare prey. Aims We evaluated individual and seasonal variation in resource selection by feral cats (Felis silvestris catus) for areas with European rabbits (Oryctolagus cuniculus) around a breeding colony of endangered black-fronted terns (Chlidonias albostriatus) in the Upper Ohau River, within the Mackenzie Basin of New Zealand. Methods Within a feral cat population subject to localised control (within a 1-km area surrounding the tern colony), we mapped the movements of 17 individuals using GPS collars, and evaluated individual and seasonal variation in third-order resource selection (i.e. within home ranges) by using resource-selection functions with mixed effects. The year was divided into breeding and non-breeding seasons for terns. Key results Three of the eight feral cats monitored during the breeding season used the colony in proportion to availability and one selected it. These four individuals therefore pose a threat to the tern colony despite ongoing predator control. Selection by feral cats for areas with high relative rabbit abundance was not ubiquitous year-round, despite previous research showing that rabbits are their primary prey in the Mackenzie Basin. Conclusions Results suggest that rabbit control around the colony should reduce use by feral cats that select areas with high relative rabbit abundance (less than half the individuals monitored), but is unlikely to alleviate the impacts of those that select areas with low relative rabbit abundance. Hence, predator control is also required to target these individuals. Results thus support the current coupled-control of feral cats and rabbits within a 1-km buffer surrounding the tern colony. Future research should determine what scale of coupled-control yields the greatest benefits to localised prey, such as the tern colony, and whether rabbits aid hyperpredation of terns by feral cats via landscape supplementation. Implications The present study has highlighted the importance of considering seasonal and individual effects in resource selection by predators, and the role of primary prey, when designing management programs to protect rare prey.

Outbreaks of house mice (Mus domesticus) occur irregularly in the wheat-growing areas of south-eastern Australia, and are thought to be driven by weather variability, particularly rainfall. If rainfall drives grass and seed production, and vegetation production drives mouse dynamics, we should achieve better predictability of mouse outbreaks by the use of plant-production data. On a broader scale, if climatic variability is affected by El Niño–Southern Oscillation (ENSO) events, large-scale weather variables might be associated with mouse outbreaks. We could not find any association of mouse outbreaks over the last century with any ENSO measurements or other large-scale weather variables, indicating that the causal change linking mouse numbers with weather variation is more complex than is commonly assumed. For the 1960–2002 period we were only partly successful in using variation in cereal production to predict outbreaks of mice in nine areas of Victoria and South Australia, and we got better predictability of outbreaks from rainfall data alone. We achieved 70% correct predictions for a qualitative model using rainfall and 58% for a quantitative model using rainfall and spring mouse numbers. Without the detailed specific mechanisms underlying mouse population dynamics, we may not be able to improve on these simple models that link rainfall to mouse outbreaks.

Abstract Context Wild house mice cause substantial economic damage to grain crops in Australia, particularly during mouse plagues. Populations were monitored to detect changes in abundance, with data from surveys used in models to forecast likely mouse outbreaks. However, it is not always feasible to use live-trapping (the 'gold standard') for assessing mouse abundance at a large number of monitoring sites spread across south-eastern Australia. A range of alternative methods was tried to assist the grains industry with strategic decisions to reduce crop damage. Aims The aim of this work was to determine which survey methods could provide useful and effective indexes of mouse abundance across a large area. Methods Monitoring of mouse populations was conducted at representative grain farms by using (1) live-trapping at long-term 'benchmark' sites (n = 2), and (2) mouse chew cards and active burrow counts at 'rapid-assessment' sites (n = 44 farms across 5 regions). Monitoring was conducted for 22 monitoring sessions over 7.5 years through low, medium and high mouse abundance conditions. Key results Live-trapping provided the most useful, but most resource-intensive, information. There were strong relationships between the index of mouse abundance from live-trapping with mouse chew cards and active burrow counts at a local (explaining 63% and 71% of variation respectively) and regional (explaining 71% and 81% of variation respectively) scales. The same quantitative relationship held between the mouse chew cards and trapping regardless of season and year. However, the relationship between active burrow counts and trapping was best in winter and autumn seasons. There was a strong relationship between mouse abundance from live-trapping and active burrows across 1 ha grids (R2 = 0.88). We determined there were 1.3 ± 0.2 (mean ± s.e.) mice per active burrow. Conclusions Live-trapping supplemented with data from chew cards and active burrows remains sufficient to monitor a wide range of sites to show regional trends. Implications It is likely that live-trapping will need to be used for the foreseeable future to provide useful parameters such as breeding condition and population abundance that are required for the forecast models. Supplementary monitoring at rapid-assessment sites (using chew cards in all seasons and active burrow counts particularly in autumn and winter), that can be collected easily without the need for animal handling, will provide additional indications of region-specific changes in mouse abundance and activity.