Chris MacGregor

A prospective longitudinal study of landscape matrix effects on fauna in woodland remnants: experimental design and baseline data

The design of a longitudinal landscape-scale “natural experiment” of Australian woodland vertebrates is described. The experiment will allow the direct study of changes in fauna inhabiting woodland fragments as the surrounding grazed landscape is transformed into a radiata pine (Pinus radiata) plantation. It will also provide data to enable the study of relationships between fauna and habitat and landscape variables, both over time and among sites. Data for terrestrial mammals, arboreal marsupials, and reptiles occurring in woodland remnants surrounded by newly planted radiata pine seedlings and pasture are presented. These data provide a reference set against which future changes in vertebrate fauna can be assessed and hence will be baseline data for the longitudinal study. Statistical analyses for several species showed that arboreal marsupials are more likely to be found in larger remnants that contain more trees with cavities and the four-fingered skink (Carlia tetradactyla) is more likely to be found either where there are more exposed rocks or more dead trees. We predict that these responses will change as the surrounding landscape matrix is transformed, particularly for arboreal marsupials such as the common ringtail possum (Pseudocheirus peregrinus), a species for which stands of radiata pine will provide suitable or partially suitable habitat.

The use of nest boxes by arboreal marsupials in the forests of the Central Highlands of Victoria

The results are reported of a nest-box study conducted in two locations in the mountain ash (Eucalyptus regnans) forests of the Central Highlands of Victoria (south-eastern Australia) to compare usage of different nest-box designs located at different heights in trees. A total of 96 nest boxes was established using a rigorous experimental design – two regions (Powelltown and Toolangi State Forests), two forest age classes (20-year post-logging regrowth and 60-year fire- and salvage-logging regrowth), two nest-box designs (large boxes with large entrance holes and small boxes with small entrance holes), and two heights at which nest boxes were attached to trees (3 m and 8 m above the ground). The study entailed setting out four nest boxes at each of 24 sites to meet the design criteria. Evidence of occupancy by vertebrates was recorded in a total of 19 of 96 boxes on 11 of 24 sites site during regular inspections over more than three years. Thirteen boxes were used by Leadbeaters possum (Gymnobelideus leadbeateri), six by the mountain brushtail possum (Trichosurus cunninghami) and seven by the common ringtail possum (Pseudocheirus peregrinus). The common ringtail possum and mountain brushtail possum were seen only in high–large boxes but Leadbeaters possum used all but the low–large boxes. There was evidence of spatial dependence in usage patterns, with all four boxes at a given site showing signs of eventually being occupied. Only two nest boxes located in mountain ash forest regenerating after the 1939 wildfires were occupied. Relatively limited use of nest boxes supports concerns about the use of a nest box over large scales and long timeframes as an effective recovery tool for species threatened by the loss and subsequent shortage in the numbers of naturally occurring hollows.

Cross‐sectional vs. longitudinal research: a case study of trees with hollows and marsupials in Australian forests

How different are insights based on cross-sectional studies from those of longitudinal investigations? We addressed this question using a detailed case study encompassing a rare suite of inter-connected cross-sectional and longitudinal investigations that have spanned the past two decades and included work on: (1) the decay and collapse of large-cavity forest trees (termed “trees with hollows”), (2) populations of a suite of species of arboreal marsupials that are reliant on trees with hollows as nesting and denning sites, and (3) relationships between the abundance, type, and condition of trees with hollows and the presence, abundance, and species richness of these animals. Our case study was from the montane ash eucalypt forests of the Central Highlands of Victoria, southeastern Australia. Our longitudinal studies led to new insights that either would not have been possible from a cross-sectional study, or which were unexpected because they did not conform, or only partially conformed, to postulated res...

What factors influence rapid post-fire site re-occupancy? A case study of the endangered Eastern Bristlebird in eastern Australia

We quantified the post-fire recovery of the endangered Eastern Bristlebird (Dasyornis brachypterus) at Booderee National Park, south-eastern Australia. Occurrence was recorded on 110 sites a year before, and for 3 years after a major unplanned fire in 2003. Although the Eastern Bristlebird is thought to be sensitive to wildfire, data indicated that the species either persisted continuously on burned sites or returned to previously occupied sites within 2 years. Post-fire site occupancy was associated with several factors: (1) pre-fire site occupancy; (2) vegetation type; (3) spatial heterogeneity in fire and the amount of unburned vegetation surrounding a site; and (4) site-level vegetation structure (e.g. diversity of understorey and midstorey plants). The most likely mechanism underpinning rapid re-occupancy was movement by resident birds to unburned parts elsewhere within their territories. The addition of intensive feral predator baiting within the present study suggests that predation may have a more important effect on populations after unplanned fires than formerly recognised. Our results have significant implications for fire management in areas where the Eastern Bristlebird occurs. Care should be taken with back-burning during unplanned fires and the spatial and temporal arrangement of prescribed fires to ensure unburned vegetation remains as refugia to facilitate bird persistence.

A survey design for monitoring the abundance of arboreal marsupials in the Central Highlands of Victoria

We describe a non-standard sample design for monitoring the abundance of arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, south-eastern Australia. The survey design is based on overlapping and rotating sampling from a given population of sites—in this case 160 sites, each measuring 1 ha in size. Estimates of population sizes are obtained using a model-based statistical analysis. Results so far reveal considerable year-to-year variability in populations of Leadbeaters Possum (Gymnobelideus leadbeateri), the Mountain Brushtail Possum (Trichosurus cunninghamii), and the Greater Glider (Petauroides volans). There appears to be an initial decline in the numbers of Leadbeaters Possum, an increase in the Mountain Brushtail Possum and no change in the Greater Glider and the total number of arboreal marsupials. It will be possible report more substantive findings about long-term trends after several more years of the program. Relationships between current and past counts for Leadbeaters Possum and Mountain Brushtail Possum were very weak. This result appeared to be due to low levels of site fidelity for these two species.

Effects of trap position, trap history, microhabitat and season on capture probabilities of small mammals in a wet eucalypt forest

In this study, we use data drawn from a series of trapping events on four 0.5-ha trapping grids surveyed in the wet eucalypt forests of central Victoria, south-eastern Australia, to identify relationships between capture probabilities and several factors of interest for three species of small mammals that are common throughout the forests of this region: the agile antechinus (Antechinus agilis), the dusky antechinus (Antechinus swainsonii) and the bush rat (Rattus fuscipes). The design of our study – four regular trapping grids – generated spatio-temporal data with binary responses and many covariates. We used powerful and relatively new statistical methodology to deal with the spatio-temporal dependence patterns in the data – analytical problems that are common in trapping data such as these modelled here. Although A. agilis, A. swainsonii and R. fuscipes are among the best studied mammals in Australia, our data analysis produced new perspectives on their probability of being captured. In particular, we quantified how capture probability is affected by trap position within a trapping grid, day of capture in a sequence of trapping days, history of trap occupancy over time by different species and sexes of those species, time of the year or season, and microhabitat attributes. Our insights are discussed in terms of their consequences for trapping protocols that might be applied in the field.

Landscape genetics of an early successional specialist in a disturbance-prone environment

Species that specialize in disturbed habitats may have considerably different dispersal strategies than those adapted to more stable environments. However, little is known of the dispersal patterns and population structure of such species. This information is important for conservation because many postfire specialists are at risk from anthropogenic changes to natural disturbance regimes. We used microsatellite markers to assess the effect of landscape variation and recent disturbance history on dispersal by a small mammal species that occupies the early seral stage of vegetation regeneration in burnt environments. We predicted that a postfire specialist would be able to disperse over multiple habitat types (generalist) and not exhibit sex‐biased dispersal, as such strategies should enable effective colonization of spatially and temporally variable habitat. We found significant differentiation between sites that fitted an isolation‐by‐distance pattern and spatial autocorrelation of multilocus genotypes to a distance of 2–3 km. There was no consistent genetic evidence for sex‐biased dispersal. We tested the influence of different habitat‐ and fire‐specific landscape resistance scenarios on genetic distance between individuals and found a significant effect of fire. Our genetic data supported recently burned vegetation having greater conductance for gene flow than unburnt habitat, but variation in habitat quality between vegetation types and occupied patches had no effect on gene flow. Postfire specialists must evolve an effective dispersal ability to move over distances that would ensure access to early successional stage vegetation. Natural disturbance and natural heterogeneity may therefore not influence population genetic structure as negatively as expected.

Refuge site selection by the eastern chestnut mouse in recently burnt heath

Context Temporal reduction in shelter is an indirect primary impact of fire. Removal of animal refugia has implications for shelter site selection and fidelity – factors that have been largely overlooked in studies of Australian rodent fauna. This information is critical for guiding species conservation and appropriate land management including prescribed burning practices. Aims We sought to determine which features of burnt heath were selected as shelter sites by the eastern chestnut mouse, whether there was sex and/or seasonal variation in shelter site selection and whether we could identify primary refugia. Methods We completed a radio-telemetry study to identify diurnal refuge sites and compare habitat attributes with those of a matched set of control sites. We then used habitat features and fidelity parameters to classify refuge site use. Key results We found the eastern chestnut mouse selected shelters with the presence of specific structures and had taller, denser vegetation than randomly selected control sites. There were no differences in habitat selection between the sexes. Shelter sites in the non-breeding season had greater vegetation density compared with those used in the breeding season. In the breeding season, the eastern chestnut mouse showed no evidence of increased fidelity to particular refuges. Vegetation density in winter was the best predictor of a primary refuge compared with whether or not an animal returned to a shelter site or the amount of time spent in a shelter site. Mice were ephemeral and non-gregarious in their refuge use. There was some evidence for inheritance of refuge sites from a parent, as well as inter-season shelter site fidelity. Conclusions The eastern chestnut mouse selected refugia that had habitat attributes offering maximum protection. Seasonality in refuge site selection is likely to reflect the reproductive and environmental trade-offs in critical resources during different seasons. The maintenance of multiple, rarely occupied shelters by the eastern chestnut mouse is consistent with data for other mammals. Implications Fire management should ensure retention of vegetation structure on the ground layer, dense habitat patches in burned areas, and be carefully planned during the winter season to maintain shelter and refuge sites to assist population persistence.

Comparing bird species richness and assemblage composition between montane ash eucalypt forest and cool temperate rainforests - an empirical study from Victoria, south-eastern Australia

Abstract Patterns of avian species richness and assemblage composition may change markedly between and within vegetation types. We compared bird species richness and assemblage composition in cool temperate rainforest and Mountain Ash (Eucalyptus regnans) forest in the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of the age of stands of Mountain Ash on the extent of forest-type differences with cool temperate rainforest. We also explored the influence of the shape of stands of cool temperate rainforest on bird species richness and the composition of the bird assemblage. We found no significant differences in bird species richness between cool temperate rainforests and Mountain Ash forest. This result was consistent with subtle differences in the composition of the bird assemblage, with few bird taxa being totally excluded from either of the two forest types. Some species (e.g. Pink Robin (Petroica rodinogaster)) were significantly more likely to be recorded in cool temperate rainforest but were not uncommon in Mountain Ash forest. We found no evidence of significant effects of stand shape in cool temperate rainforest, which was consistent with analyses of bird assemblages given that most species occurred in both forest types. Hence, we uncovered no evidence of specialist taxa confined to cool temperate rainforest.

Aves, Tumut, New South Wales, South-eastern Australia

A large-scale, long-term study of the impacts on vertebrates of landscape change and habitat fragmentation is taking place at Tumut in southern New South Wales, south-eastern Australia. Field surveys focus on counting birds within three broad kinds of sites in the study region. These are: (1) A randomized and replicated set of 85 sites in remnants or fragments of native Eucalyptus forest located within the boundaries of the Radiata Pine plantation. (2) Sites dominated by Radiata Pine plantation trees (N = 40 sites). (3) Sites in the large areas of continuous Eucalyptus forest adjacent to the plantation that act as controls (N = 40 sites). We list of birds recorded during 1996 and 1997. A total of 92 species from 34 families was recorded. The list will be useful for workers examining bird responses to fragmented landscapes as well as those interested in the biodiversity values of plantation landscapes.