Chapter 5 Feeding Ecology of the Australian Raven on Rottnest Island

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Early observers did not document <strong>the</strong> Quokka density on Rottnest Island, but it is assumed that numbers were ‘abundant’ compared to mainland populations (Storr 1963). The establishment <strong>of</strong> crops and exotic herbivorous plants provided an additional food source for Quokkas, but hunting by aboriginal prisoners, vice-regal parties and later tourists, kept <strong>the</strong> population from proliferating (Storr 1963; Pen and Green 1982). In 1917 <strong>the</strong> species was declared protected and shooting was prohibited (Rippey et al. 2003). The population increased rapidly and by <strong>the</strong> early 1930s <strong>the</strong>y had exploded, <strong>the</strong> increase coinciding with <strong>the</strong> observed fragmentation <strong>of</strong> Acacia rostellifera scrub (Storr 1963). Acacia, in particular its new suckers, are extremely palatable to Quokkas and within two years overgrazing can quickly remove this species from <strong>the</strong> matrix, where it is <strong>the</strong>n replaced by fire resistant and unpalatable herbs and low shrubs (Storr et al.1959; Storr 1963).While land clearing and fires have removed <strong>the</strong> majority <strong>of</strong> <strong>the</strong> melalluca and callitris forests, over grazing by Quokkas has impeded <strong>the</strong> growth <strong>of</strong> acacia, leaving <strong>the</strong> dominant vegetation community <strong>of</strong> Rottnest Island as depauperate, schlerophyllous grassy heathlands (Rippey et al. 2003), a great contrast from <strong>the</strong> descriptions <strong>of</strong> early explorers. In an effort to repair <strong>the</strong> habitats <strong>of</strong> Rottnest Island a management plan, <strong>the</strong> Woodland Restoration Program, has been implemented. In <strong>the</strong> past decade <strong>the</strong> program has planted over 242,000 trees in fenced plantations (Rottnest Island Authority 2009), with an aim to return <strong>the</strong> woodlands <strong>of</strong> <strong>the</strong> island to connect remnant woodland habitats and return Rottnest to reflect what was described by <strong>the</strong> first colonial settlers. Such drastic changes to <strong>the</strong> vegetation over <strong>the</strong> last two hundred years have impacted heavily on <strong>the</strong> terrestrial bird species that use <strong>the</strong>se habitats, leading to <strong>the</strong> decline or local extinction <strong>of</strong> several habitat sensitive species. O<strong>the</strong>r species have responded positively by increasing in both distribution and abundance. The change in status <strong>of</strong> bush birds on Rottnest and <strong>the</strong>ir current distribution is examined below. 14
Figure 2.3: Major vegetation associations <strong>of</strong> Rottnest Island as <strong>of</strong> 2010. Revegetation plantations are outlined in red. GIS Imaging source used under WALIS Licence for <strong>the</strong> non-commercial use <strong>of</strong> land information provided by <strong>the</strong> Government <strong>of</strong> WA, courtesy Rottnest Island Authority 2011. 15
Page 1: Ecological Impacts of</stro
Page 5 and 6: Abstract The Australian</st
Page 7 and 8: Contents Acknowledgements vii <stro
Page 9 and 10: 5.2.2 Laboratory examination <stron
Page 11 and 12: Acknowledgements My sincerest thank
Page 13 and 14: Chapter 1 Introduc
Page 15 and 16: 1.2 Why is the <st
Page 17: Chapter 5 Investig
Page 20 and 21: 2.1.2 History Archaeological eviden
Page 22 and 23: Figure 2.1: Rottnest Island in rela
Page 24 and 25: Figure 2.2b: Rottnest Island with t
Page 29 and 30: 2.2 Methods 2.2.1 Literature review
Page 31 and 32: 2.3 Results 2.3.1 History o
Page 33 and 34: Genus species Common Name Habitat S
Page 35 and 36: Gerygone fusca Western Gerygone W R
Page 37 and 38: Increases Twelve species have incre
Page 39 and 40: diversity (Figure 2.5). These sites
Page 41 and 42: 13 Figure 2.5: Combned monthly freq
Page 43 and 44: some species, but causing t
Page 45 and 46: smaller in size than the</s
Page 47 and 48: Pest Management Plan, with 180 indi
Page 49 and 50: within the settlem
Page 51 and 52: Figure 3.1: Age characteristics <st
Page 53 and 54: highest daily frequency of<
Page 55 and 56: individuals in the
Page 57 and 58: pair of Osprey als
Page 59 and 60: There were a higher number
Page 61 and 62: and multiple nests support
Page 64 and 65: Chapter 4 Nest Pre
Page 66 and 67: 4.1.3 Hypothesis t
Page 68 and 69: To reduce the impa
Page 70 and 71: The outside of <st
Page 72 and 73: Five nests, one of
Page 74 and 75: 4.2.8 Control - naturally occurring
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Total Settlement (a) Nests SITE 1 5
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Figure 4.4: Linear regression test
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This can be explained by th
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Chapter 5
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conducted in 2011 (May - September)
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Figure 5.1: Sources of</str
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Figure 5.2: Raven
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Food Category (i) Seed/Plant Grit/
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Initially, culling was conducted at
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settlement for foraging, roosting a
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6.3 Recommendations for future rese
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Given that several bush bird specie
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Program may already be influencing
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Appendices Appendix I Characteristi
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49 2 B 49 11/10/2010 GW Exposed YES
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101 5 C 101 8/11/2010 LTD Exposed Y
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Appendix II Summary: Nest predation
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Appendix IV Summary: Nest predation
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References Alexander, W.B. (1921).
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Burbidge, A.A. (2010). Australia’
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Glauert, L. (1929). Contributions t
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Major, R.E., Pyke, G.H., Christy, M
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Ricklefs, R.E. (1969). An analysis
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Skutch, A.F. (1966). A breeding bir
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Chapter 5 Feeding Ecology of the Australian Raven on Rottnest Island

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