Reference: The Australian Museum. The Australian Museum. Updated March Can you Help? Site Map. Contact us. Red-Legged Pademelon. Red-Necked Pademelon. Red-Neck Wallaby. Swamp wallaby. Whiptail wallaby. Rufous Bettong. The Swamp Wallaby feeds on a variety of plants including introduced and native shrubs, grasses and ferns. Like many marsupials, female Swamp Wallabies can suckle two joeys of different ages. The pouch life of each joey is eight to nine months, although they may continue to suckle until 15 months of age.
The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands. Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden.
This website uses cookies to ensure you get the best experience on our website. M and F refer to male and female, respectively. More than 1 wallaby was shot at 5 of the 14 sites Table 1 , and in each case intrasite home ranges overlapped to some degree.
At the 5-year-old site where 5 wallabies were shot, home-range overlap ranged from 5. The home ranges of wallabies shot at different sites did not overlap. All wallabies were shot in autumn, 12 during April and 10 during March , with each habitat type being represented in each year. In both cases the preceding summer had been dry and autumn rain had not begun at the time of shooting. Shooting was conducted in accordance with the Code of Practice for the Humane Shooting of Kangaroos Environment Australia , and all procedures associated with animals were approved by the Melbourne University Faculty of Science Animal Experimentation Committee and meet guidelines of the American Society of Mammalogists for animal care and use Gannon et al.
A pooled sample was used to reflect an extended consumption period that was consistent with forage availability sampled from within the whole home range. Diet analysis. After additional rinsing, dyed material was suspended in corn syrup, and placed on 3 or 4 microscope slides sealed with nail polish.
The plant fragment closest to each grid intersection defined by crosshairs was identified on the basis of microhistological features e. Very few sedges were positively identified, so grass and sedges were collapsed into a single monocotyledon category. In almost every case, ferns were austral bracken. The number of fragments belonging to each plant group was expressed as a proportion of the total number successfully identified.
Using reference slides containing fragments with the same size distribution as the stomach contents, the proportion of identifiable fragments in each plant group was determined. These slides were prepared as described above except that fragments were left in the sodium hypochlorite solution for 3 h. These data were used to correct the raw values for bias resulting from unequal rates of identification between plant groups Norbury Data analysis.
Overall diet consumption and selection at unharvested-forest and 5-year-old regenerating sites was analyzed with nonmetric multidimentional scaling using the Bray Curtis distance measure.
Consumption data were expressed as the proportion of each plant group found in the gut of each wallaby and selection was expressed using a standardized selection index, , where u ij and a ij are the proportion used and available respectively of food type i , for wallaby j. The values for this index range from 0 to 1 and are interpreted as the probability that a food type would be the next selected if all food types were equally available Manly et al.
Before analysis, raw data were subjected to a range standardization so that all values were expressed as a percentage of the maximum.
A multiresponse permutation procedure Mielke et al. Compositional analysis Aebischer et al. When food types were available but not used, the 0 use value was replaced by 0. In cases where food types were neither used nor available, values were treated as missing but replaced by the mean of nonmissing values to calculate the ranking matrix.
Analyses were conducted using Compos Analysis 6. In the 2nd analysis, between 1 and 6 data points were necessarily excluded from the model for each food type because of missing data. In the 3rd analysis, transformation was not conducted because the model was developed for use with raw data B. Manly, pers. In this case, up to 2 outliers were removed from each data set to meet analytical assumptions, although variances in the tree-selection model were still somewhat heterogeneous.
Consequently, the forb and tree models were rerun using traditional multiple regression after excluding the relative availability of trees and forbs, respectively. All regression analyses were conducted in Minitab Regardless of the habitat, forbs constituted the major portion of the wallabies' diets, with moderate amounts of shrubs and grass also consumed.
The consumption of trees and ferns was very low in the unharvested-forest sites, but rose to moderate levels at 5-year-old sites. The consumption of ferns, forbs, and trees differed substantially between unharvested-forest and 5-year-old sites, as did the relative availability of forbs, monocots, and trees Table 2.
On the basis of the estimated effects and their associated errors, our interpretation is that moderate to large changes in selection are likely to exist in the population of interest, but additional data are required to estimate effects with a higher degree of precision.
B is a standardized index of diet selection see text. Confidence intervals around the selection index are in parentheses, and were derived using a bootstrapping procedure to account for asymmetry in some of the data sets.
Random feeding i. Because of the presence of outliers, medians were used as a measure of central tendency. At unharvested sites compositional analysis indicated that the most highly selected food type was shrubs followed by forbs, trees, monocots, and ferns. At 5-year-old sites the most highly selected type was forbs followed by shrubs, ferns, monocots, and trees.
Comparisons of selection between different food types Fig. Major differences between the unharvested-forest and 5-year-old sites Figs. In addition, all estimates are relatively precise at 5-year-old sites, indicating reduced variation between individuals. Effects are expressed as the 1st named food type minus the 2nd named food type, so positive values mean the 1st named type is selected to a greater degree.
Overall diet composition differed substantially between unharvested-forest and 5-year-old sites Fig. Relative to wallabies living at 5-year-old sites, individuals at unharvested-forest sites ate more forbs and less ferns and trees Table 2 , and this was reflected by the strong linear correlations between these food types and ordination axis 2 Table 3.
Unharvested-forest and 5-year-old sites were more similar in terms of overall selection, although the P -value was still small Fig. The effect-size index A showed that the observed difference in diet selection was about 4 times smaller than the difference in diet composition. On the basis of linear trends Table 3 , the difference was associated with selection of shrubs and forbs, with wallabies in the unharvested forest selecting shrubs more strongly and forbs less strongly Table 2.
A bubble plot not shown indicated that selection of ferns had a strong nonlinear association with the difference between groups, with wallabies at 5-year-old sites selecting ferns more strongly.
Linear correlations Pearson's correlation coefficient, r between food types and the ordination axis for both diet composition and selection. Ordination diagrams representing a the use consumption and b the selection of plant groups by swamp wallabies Wallabia bicolor. Vectors solid lines represent the strength and direction of the linear correlation between individual food types and the ordination axis see Table 3 for coefficients. The labels 1 and 2 in diagram b indicate outlying points see text for details.
Wallabies at 5-year-old sites formed 2 distinct clusters along axis 2 in Fig. The group of 4 lower on axis 2 selected shrubs to a greater extent and forbs to a lesser extent than their counterparts. The labeled points in Fig. In the case of monocots, there was a moderate but imprecise negative relationship and the inference remains uncertain. Univariate models of frequency dependence for each of the 5 food types.
In stage 2 of the analysis Table 5 , relative availability was a substantial negative predictor of selection for every food type except shrubs, whereas in most cases the 3 forage quality variables were poor predictors. On a number of occasions e. In the case of the tree model, however, both nitrogen and water content showed moderate positive correlations with selection, indicating that along with relative availability, these variables may have influenced the selection of tree foliage to some degree.
The coefficients in Table 5 are standardized and are directly comparable to those in Table 4. Multivariate models for each food type comparing the effect of relative availability and forage quality on diet selection.
The sample size n is less than 22 because of missing data. Stage 3 of the analysis Table 6 presents multivariate models relating diet selection of each food type to the relative availability of all foods.
The original models constructed using Manly's technique showed, in every case, that selection of a food was independent of its own relative availability but positively correlated with the relative availability of at least 1 other type.
In the case of the forb and tree models, however, the strong correlation between the relative availability of forbs and trees made the coefficients associated with these food types difficult to interpret. After removing the tree data from the forb model and the forb data from the tree model, selection of both food types was negatively correlated with its own relative availability.
Multivariate linear models for frequency-dependent selection constructed using the technique of Manly —see text for details.
For each model, the response variable is the selection index B and the predictors are the relative availability of each food type the P s. Interpreted as strong evidence for a positive correlation between tree selection and forb relative abundance because the lower confidence limit only just overlaps 0.
In this study, we used vegetation change resulting from timber harvesting to investigate diet composition and selection in a wild population of swamp wallabies. Diet composition differed substantially between unharvested-forest and 5-year-old sites, and the results confirm the status of the swamp wallaby as a generalist herbivore that consumes a wide variety of foods, including low-quality forage such as austral bracken and Eucalyptus foliage Edwards and Ealey ; Hollis et al.
The ability to process low-quality foods is consistent with the species' common status and wide geographic distribution Menkhorst , and the observed westward expansion of its range into southwestern Victoria Bird In general, our findings were similar to the only other study of diet selection for this species Wood , in which shrubs and forbs also were identified as important dietary components.
Wood used fecal pellets to derive selection indices for plant functional groups within 2 vegetation communities during 2 seasons, and observed differences in selection associated with both factors. Although no formal analysis was conducted, Wood found that increased selection for forbs during summer was associated with reduced forb availability, and this is consistent with the negative relationship between forb selection and availability that we observed.
A marked change in overall diet composition between unharvested and 5-year-old sites was mirrored by a smaller but distinct difference in selection. The latter effect was primarily driven by changed selection for forbs, shrubs, trees, and ferns, and the selection ranking of trees and ferns changed substantially between sites. Nevertheless, at both unharvested and 5-year-old sites, wallabies consistently selected forbs and shrubs over monocots and trees, demonstrating that generalist mixed feeders may still exhibit distinctive foraging choices Tixier et al.
However, it is important to note that differential selection for shrubs at unharvested and 5-year-old sites may have been influenced by the presence of different species.
Although most unharvested sites had a mix of shrubs including silver wattle, prickly wattle, common heath, gorse bitter-pea, and common cassinia, the shrub flora at 5-year-old sites was dominated by silver wattle, and this difference confounds the selection results to some degree. Our initial prediction, that wallabies would be mixed feeders and demonstrate negative frequency dependence, was strongly supported by univariate models for ferns, forbs, and trees.
The multivariate models that included forage-quality variables suggested similar patterns, although in this case monocots also demonstrated negative frequency dependence. Recently, Bergvall and Leimar showed that the effect of relative availability on selection may be altered by forage quality, but, with the exception of trees, the forage-quality indicators used in this study did not appear to influence selection, strengthening the inference regarding relative availability.
However, the positive correlation between the selection of tree foliage and both its nitrogen and water content suggested that the observed pattern of tree selection was influenced by both relative availability and forage quality, although relative availability appeared to have a stronger effect. The use of Manly's method for the analysis of frequency dependence, and our modification to account for correlations between predictors, indicated that the selection of all food types except for trees was related to the relative availability of at least 1 other type.
This result confirms the intuitive expectation that diet selection is a complex process that depends, among other factors, on the availability and quality of alternative forage, although we do not discount the possibility of spurious results given the relatively large ratio of predictors to experimental units.
In the context of commercial forestry, Welch et al. Selection of a food type may be influenced by the nutrient status of other foods Moser et al. Swamp wallabies have been found to consume substantial amounts of grass in spring when, relative to other available food types, its nitrogen concentration was high Osawa Data across seasons incorporating selection, availability, and information about forage quality e. The 3 analyses of frequency dependence present an increasingly complex picture of the factors influencing diet selection.
Overall, the data provide substantial support for negative frequency dependence and a mixed feeding strategy, which may be driven by a need to consume a variety of nutrients Pulliam ; Westoby or minimize the detrimental effects of plant toxins.
In no case did the data support diet specialization positive frequency dependence , and on this basis it appears that the foraging strategy of swamp wallabies does not conform to the predictions of optimal foraging theory.
The general lack of support for the optimal diet model is not particularly surprising, because some of its assumptions probably do not apply to mammalian herbivores. For example, simple optimal diet models assume that the time taken to search for and handle food items are mutually exclusive Pyke et al.
In addition, searching costs are likely to be very low for animals that consume large quantities of abundant food Westoby and thus may have little effect on food choice. These and other factors e. Finally, the results of this study relate to the consumption of broad plant groups in autumn within areas defined by home-range boundaries and should not be extended to other times or spatial scales. Presumably wallabies also selected species within plant groups and patches within home ranges, thus data at a finer spatial resolution may have revealed different patterns.
In addition, swamp wallabies may select forage with a relatively high nitrogen content Osawa ; thus, our conclusions may have been different if stomach samples had been collected in another season.
Collecting data at the scale at which behavior takes place will facilitate accurate inference Wiens , but it is not always obvious what that scale is, or indeed if multiple scales are important.
Studies at a variety of spatial scales, and consistency of results between them, can strengthen the generality of findings from any one investigation Bowyer and Kie ; Ward and Saltz For swamp wallabies, it will be instructive to see if the current support for models predicting mixed feeding also is found in different seasons and when data are collected at a finer resolution. Thanks to G. Hepworth for statistical advice and M.
Flett for facilitating field work. Flett and R. Moyle did the shooting, for which we are much obliged. This research was conducted in conjunction with Department of Sustainability and Environment permit and Melbourne University Faculty of Science Animal Experimentation Committee permit Aebischer N. Robertson P. Kenward R. Compositional analysis of habitat use from animal radio-tracking data.
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