Academic literature on the topic 'Setonix brachyurus'

We investigated the consumption of milk by the young quokka using the stable isotope deuterium oxide. The volume of milk consumed increased from 1.6 mL day–1 at 55 days post partum to 32.5 mL day–1 at 165 days. The daily energy intake ranged from ~22 to 151 kJ day–1 during pouch life. The crude growth efficiency (grams of growth per millilitre of milk consumed) increased from an average of 0.35 to 0.46 g mL–1 in the early stages of pouch life, and then decreased to 0.24 g mL–1 during Phase 2b of lactation. The crude growth efficiency measured in our study indicates that quokkas are equally efficient in converting milk energy to body mass as other marsupials reported in the literature. Measuring milk intake with this method offers a non-toxic, minimally invasive alternative to other techniques for measuring milk consumption in marsupials, when milk is the only source of water intake.

While preparing a review of published descriptions of copulatory behaviour in macropod marsupials (McLean, Lundie-Smith and Jarman 1993), we were surprised to find no description for one of the most studied species, the quokka (Setonix brachyurus, e.g. see Bradshaw 1983). Copulating quokkas have been seen previously by researchers (e.g. Kitchener 1970), but no account was given. Here we provide descriptions of copulatory behaviour in quokkas, and comment on levels of sexual behaviour and activity by quokkas in the wild and in captivity.

We investigated the composition of the milk of the quokka between 70 and 300 days post partum. From 70 to 180 days, the mean concentration of protein in the milk was 63.5 ± 6.50 g L−1. The protein levels then began to increase, peaking at 120 g L−1 towards the end of lactation. The mean lipid and total solids content were 45.0 ± 6.50 and 175.0 ± 11.77 g L−1 from 70–180 days, increasing to 150 and 250 g L−1 after permanent pouch exit. In contrast, the total carbohydrate concentration of the milk decreased from 80 to 20 g L−1 at 150 days. The concentration of lactose started to decrease at 180 days from 30 to 10 g L−1, and galactose and glucose began to rise from 1 to 9 g L−1 and 0.5 to 4.0 g L−1, respectively. The milk lipid consisted mainly of long- and medium-chain fatty acids, with no short-chain fatty acids detected. The major fatty acids present were palmitic and oleic acids, followed by linoleic, trans-vaccenic and stearic acids. The percentage composition of oleic and stearic acids varied significantly during lactation. The composition of the milk of the quokka changed during lactation, coincident with the young reaching critical milestones in its development. This finding supports the hypothesis that the composition of the milk changes to meet the nutritional needs of the developing young.

The quokka (Setonix brachyurus Quoy & Gaimard 1830) is a medium-sized, macropodid marsupial that is endemic to the mesic, south-western corner of Australia. While being a tourist icon on Rottnest Island, the species is threatened with extinction. It has been intensively studied on Rottnest Island in the 1960s and 1970s, however very little is known of its ecology on the mainland. Additionally the insular and mainland environments are extremely different suggesting that ecological differences between the two populations are likely. Consequently, this study sought to determine the basic autecology of the quokka and identify what factors have attributed to its threatened conservation status. The northern jarrah forest of Western Australia was selected as the study region due to it being at the northern limit of extant quokka distribution and because it was thought that the factors threatening the quokka would be exacerbated there. Fossil deposits suggest that the quokka originally occupied an area of approximately 49,000 km2 in the south-western corner of Australia. Historical literature show that they were widespread and abundant when Europeans colonised the region in 1829 but a noticeable and dramatic decline occurred a century later. The arrival of the red fox to the region coincided almost exactly with this decline and so it was probably ultimately responsible. Continued predation by both it and the feral cat are likely to have continued the decline, along with habitat destruction and modification through altered fire regimes. Specific surveys and literature searches show that since the 1950s, the area occupied by the quokka has declined by 45% and since 1990 by 29%. Based on the criteria of the IUCN (Hilton-Taylor 2000), the conservation status of the quokka should remain as vulnerable. An endangered status may be more applicable if the quokkas restriction to patches through its existence as a metapopulation is considered. Trapping of eight sites supporting quokka populations in the mid-1990s revealed three sites now locally extinct despite the ongoing, six year old, fox control programme. Another three are at serious risk of extinction. Extant population sizes ranged from one to 36 and population density ranged from 0.07 to 4.3 individuals per hectare. This is considered to be below the carrying capacity of each site. The overall quokka population size in the northern jarrah forest may be as low as 150 adult individuals, of which half are likely to be female. Even the largest extant populations are highly susceptible to stochastic extinction events. This small size was surprising considering the six year old, introduced predator control programme. Historically, the restriction to discrete habitat patches, the occasional inter-patch movement, the lack of correlation between the dynamics of each population and reports of frequent localised extinctions and colonisations suggest that the quokka population once existed as part of a classic metapopulation. The massive decline of the quokka in the 1930s pushed the metapopulation structure into a non-equilibrium state such that today, the extant populations are the terminal remnants of the original classic metapopulation. Wild mainland quokkas breed throughout the year. A significant reduction in the number of births occurs over summer and this coincides with a decline in female body weight. Despite this, the mainland quokka is relatively fecund and is able to wean two offspring per year. The level of recruitment from pouch young to independence was low and this may explain the apparent lack of population increase following the initiation of fox control. A total of 56 trapped quokkas were fitted with a radio collar. Mean home range size for quokkas was 6.39 ha with a core range of 1.21 ha and this was negatively related to population density. Male home ranges were larger than females but not significantly when the sexual size dimorphism was considered. Nocturnal ranges were larger than diurnal ranges reflecting nocturnal departures from the swamp refugia. Home range sizes varied seasonally, probably due to changes in the distance required to move to obtain sufficient nutrients and water over the dry summer compared to the wet winter and spring. Telemetry confirmed trapping results that showed no movement between swamps or populations. Home range centres shifted to the periphery of the swamp following the winter inundation and this may increase the species susceptibility to predation. The lack of dispersal is probably caused by quokka populations existing below carrying capacity and following selection for philopatry under the threat of predation for dispersing individuals. Without dispersal to recolonise or rescue unpopulated patches, the collapse of the original quokka metapopulation appears to have occurred. On a macrohabitat scale, the quokka in the northern jarrah forest is restricted to Agonis swamp shrubland habitats that form in the open, upper reaches of creek systems on the western side of the forest. This restriction was probably initially due to the high water requirements of the quokka but is likely to have been exacerbated by increased predation pressure since the arrival of the fox. On a microhabitat scale, the quokka is a habitat specialist, preferring early seral stage swamp habitats, probably for foraging, as part of a mosaic of old age swamp that provides refuge. Despite the six year old, introduced predator control programme, foxes and cats are still the major cause of mortality to quokkas. Road kills was the other identifiable cause. Individuals alive at the start of the study had an 81% chance of staying alive until the end. The likelihood of dying was minimised by grouping together with conspecifics, maximising home range size and maximising the time spent within the swampy refuge. Current rates of adult and juvenile survivorship should allow population recovery and so it seems pouch young mortality, reflected by low recruitment, has inhibited the anticipated population increase following predator control. The confounding effect of inadequate unbaited controls meant that little statistical evidence was available on the impact of introduced predators on the quokka, however the models provided support for earlier hypotheses of these. The presence of a quokka population at a site was related to the amount of poison baits delivered ??? reflecting predation pressure, the average age of the swamp and a mosaic of early and late seral stages within the swamp habitat. Recently burnt habitat is thought to provide food for quokkas and long unburnt habitat provides refuge from predation.

[Truncated abstract] Previous studies suggest that the milk of the quokka (Setonix brachyurus) could change composition coincident with critical stages of development of the young, and that the milk energy provided by the mother and its utilisation by the joey would determine the young’s growth rate. To test this general hypothesis, quokkas (n = 19) were bred in captivity and milk was collected during lactation. The samples were analysed using specific biochemical assays and sensitive analytical techniques to determine the composition of the milk of the quokka. The stable isotope, deuterium oxide, was employed to estimate the volume of milk consumed by the joeys. The adult females and their young were weighed and body measurements taken periodically, in order to calculate the body condition of the adults and monitor the growth rate of the offspring. Marsupial lactation can be divided in three phases. Phase 1 of lactation covers the period during pregnancy. Phase 2a of lactation in the quokka (0 to 70 days post partum), is the period when the young is permanently attached to the teat, while Phase 2b (70 to 180 days post partum) is when the joey suckles intermittently but is still confined to the pouch. Phase 3 of lactation extends from the time when the young initially emerges from the pouch to the end of lactation (180 to 300 days post partum) ... The metabolism of fatty acids in quokkas appears to be a combination of the processes in monogastric and ruminant mammals. The growth rate of the young quokkas was dependent on the volume and energy content of the milk consumed. The crude growth efficiency indicates that quokkas are equally efficient as other marsupials reported in the literature, in converting milk energy to body mass. It seems that female quokkas maintained energy balance during lactation, most probably by increasing their food intake rather than mobilising body fat stores. In addition, it appears that quokkas are capable of producing young of similar mass, irrespective of their own body weight or condition, when they have access to an adequate supply of food and water. This was the first study to provide detailed information about milk composition and lactational energetics in the quokka. While the results supported the unifying hypothesis in relation to the major changes associated with the transition through the phases of lactation, wide variations were detected between the quokka and other marsupial species in the changes in the detailed composition of milk and milk production.

Thesis (Ph. D.)--University of New South Wales, 2002.
Title from PDF title page (viewed Sept. 19, 2007). Made available through Australian Digital Theses Program. Includes bibliographical references.