Chapter 5 Feeding Ecology of the Australian Raven on Rottnest Island

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<strong>Chapter</strong> 3 Biology and <strong>Ecology</strong> <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> on Rottnest Island 3.1 Introduction and Aims The increase <strong>of</strong> <strong>the</strong> abundance <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> on Rottnest Island over <strong>the</strong> last century has been well documented, but little detailed study into <strong>the</strong> distribution or biology <strong>of</strong> <strong>the</strong> species has been conducted. For <strong>the</strong> most part, previous authors have simply commented on <strong>the</strong> raven’s abundance without fur<strong>the</strong>r investigation. In this chapter, I will quantify recent observations <strong>of</strong> ravens recorded during this project, and identify how ravens use <strong>the</strong> landscape by assessing <strong>the</strong>ir current distribution, abundance and population status on Rottnest Island. 3.1.1 Taxonomy <strong>of</strong> <strong>Australian</strong> corvids Birds <strong>of</strong> <strong>the</strong> family Corvidae (<strong>the</strong> corvids) appear to have evolved from a forest-living ancestor out <strong>of</strong> Australia, which radiated out <strong>of</strong> <strong>the</strong> Australo-Papuan region into Asia during <strong>the</strong> late Oligocene and Miocene (Ericson, Irestedt and Johannsson 2003; Ericson, Johannsson and Ekman 2005). Monroe and Sibley (1993) list twenty-three genera comprising <strong>of</strong> 118 species, with a worldwide distribution including <strong>the</strong> nor<strong>the</strong>rn hemisphere choughs (Pyrrhocorax), nutcrackers, jays, <strong>the</strong> rook and Eurasian magpies. The crows and ravens, genus Corvus, are all large to very large, black, grey or black and white birds, with strong legs and feet, large bills and wings (Goodwin 1976). There are five <strong>Australian</strong> native species <strong>of</strong> corvid, all belonging to <strong>the</strong> genus Corvus (C. coronoides <strong>Australian</strong> <strong>Raven</strong>; C. tasmanicus Forest <strong>Raven</strong>; C. mellori Little <strong>Raven</strong>; C. bennetti Little Crow; and C. orru Torresian Crow) (Higgins, Peter and Cowling 2006). The House Crow C. splendens occasionally occurs as an accidental visitor (ship assisted), including on Rottnest Island (Department <strong>of</strong> Agriculture and Food 2006). It has successfully been prevented from establishing in Australia. Three species are found in Western Australia: <strong>the</strong> Torresian Crow in <strong>the</strong> nor<strong>the</strong>rn and northwest regions, <strong>the</strong> Little Crow in <strong>the</strong> arid regions and <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> <strong>of</strong> <strong>the</strong> southwest. There is a clinal decrease in size <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> from east to west, with <strong>the</strong> southwestern subspecies C. corronoides perlexus being 32
smaller in size than <strong>the</strong> nominate subspecies <strong>of</strong> eastern Australia (Rowley 1970). The south western subspecies may be elevated to a full species following molecular research (L. Jospeh 2 pers. comm. 2011). 3.1.2 Life history <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> Extensive research into <strong>the</strong> biology <strong>of</strong> <strong>Australian</strong> corvids, including <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong>, was conducted principally by Ian Rowley in <strong>the</strong> 1960s, and published from 1967 to 1974. Observations <strong>of</strong> <strong>the</strong> biology, behaviour, habitat and ecology <strong>of</strong> corvids were collected during studies investigating predation on lambs by <strong>the</strong>se species in sou<strong>the</strong>astern Australia (Rowley 1973a; Rowley 1973b; Rowley, Braithwaite and Chapman 1973). Much <strong>of</strong> what is known <strong>of</strong> <strong>the</strong> biology and behaviour <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong>, and o<strong>the</strong>r <strong>Australian</strong> corvids, has been gleaned from <strong>the</strong>se studies and is summarised below, except where acknowledged. <strong>Australian</strong> <strong>Raven</strong>s reach breeding maturity at three years with eggs laid between May and October in Western Australia (Storr and Johnstone 2004). A large bowl-shaped nest is built by both sexes in a fork <strong>of</strong> <strong>the</strong> crown <strong>of</strong> <strong>the</strong> highest tree in <strong>the</strong> territory, but <strong>the</strong>y will also use artificial structures (Rowley 1973b). The nest is constructed from sticks, twigs and rootlets being lined with bark, grass, wool and hair (Higgins et al. 2006), and may be reused with new material being added each year. Up to two to six eggs are laid on successive days and incubated for 19-20 days by <strong>the</strong> female only. The female broods <strong>the</strong> nestlings for <strong>the</strong> first two weeks, with both chicks and female being fed by <strong>the</strong> male. After this time both sexes will feed young up until fledging at around 40-45 days. Fledglings remain in or close to <strong>the</strong> nest tree at first, moving fur<strong>the</strong>r and fur<strong>the</strong>r away over <strong>the</strong> following weeks, and may remain in <strong>the</strong> territory for up to four months after which time <strong>the</strong>y join non-breeding dispersive flocks. First year birds may return to <strong>the</strong>ir natal area <strong>the</strong> following year. <strong>Raven</strong> pairs maintain territories <strong>of</strong> approximately 1200m 2 . The territory is held by <strong>the</strong> male and is used all year round for feeding, roosting and breeding, and is defined by landscape features 2 Dr. Leo Joseph Research Director & Curator, <strong>Australian</strong> National Wildlife Collection CSIRO Ecosystem Science, Crace ACT 33
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 26 and 27: Early observers did not document <s
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: some species, but causing t
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
Page 76 and 77: Total Settlement (a) Nests SITE 1 5
Page 78 and 79: Figure 4.4: Linear regression test
Page 80 and 81: This can be explained by th
Page 83 and 84: Chapter 5
Page 85 and 86: conducted in 2011 (May - September)
Page 87 and 88: Figure 5.1: Sources of</str
Page 89 and 90: Figure 5.2: Raven
Page 91 and 92: Food Category (i) Seed/Plant Grit/
Page 93: 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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