Chapter 5 Feeding Ecology of the Australian Raven on Rottnest Island

The six bush bird species examined here are species <strong>of</strong> conservation importance and in some
cases may be unique to Rottnest Island, as described below. The Golden Whister, White-
browed Scrubwren, White-fronted Chat are also <strong>of</strong> concern on <strong>the</strong> adjacent Swan Coastal Plain
(Recher and Serventy 1991; How and Dell 1993), while <strong>the</strong> Red-caped Robin is absent from
much <strong>of</strong> <strong>the</strong> Swan Coastal Plain. The distributions <strong>of</strong> Golden Whistler and White-browed
Scrubwren are reduced in <strong>the</strong> Perth area, with <strong>the</strong> whistler now almost entirely restricted to
<strong>the</strong> heavily wooded areas <strong>of</strong> <strong>the</strong> Darling Scarp (Davis and Brooker 2008). White-browed Scrub-
wren and White-fronted Chat are restricted in <strong>the</strong>ir distribution on <strong>the</strong> Swan Coastal Plain, and
<strong>the</strong>ir preferred habitats may be threatened by rapid urban development. The populations on
Rottnest Island may represent a safe-haven for <strong>the</strong>se species, protected from fur<strong>the</strong>r decline by
<strong>the</strong>ir isolation.
In addition, three <strong>of</strong> <strong>the</strong>se species differ morphologically or behaviourally from <strong>the</strong>ir nearest
mainland populations. The Singing Honeyeaters <strong>of</strong> Rottnest Island has been proposed as a
distinct species from birds <strong>of</strong> <strong>the</strong> mainland, based on <strong>the</strong> robustness <strong>of</strong> its appearance and
differences in plumage colouration (Milligan 1911; Wooller et al.1985), but this
recommendation has not been recognised in recent revisions <strong>of</strong> <strong>Australian</strong> avian taxonomy
(Christidis and Boles 2008; Johnstone 2010). Similarly <strong>the</strong> Red-caped Robin and Western
Gerygone have been suggested to differ from <strong>the</strong> mainland population (Saunders and de
Rebeira 1985), as both differ in <strong>the</strong>ir calls when compared to birds in <strong>the</strong> southwest (Baker,
Baker and Baker 2003a; Baker, Baker and Baker 2003b). Fur<strong>the</strong>r research into <strong>the</strong> status <strong>of</strong>
<strong>the</strong>se population variants needs to be conducted to determine <strong>the</strong>ir true relationship to
mainland populations.
The major threatening processes to island birds are in general anthropogenically derived
processes being exploitation by humans: habitat loss, degradation and fragmentation;
increased fire regimes; introduced species and direct predation (Whittaker and Fernandez-
Palacois 2007). Hunting and <strong>the</strong> live trade <strong>of</strong> birds are now no longer threats to birds on
Rottnest Island, but <strong>the</strong> o<strong>the</strong>r threats still remain. Habitat loss and fragmentation through land
clearing and increased fire regimes has drastically altered <strong>the</strong> Rottnest landscape favouring
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