Chapter 5 Feeding Ecology of the Australian Raven on Rottnest Island

Although <strong>the</strong>re has been a continued and expressed concern by <strong>the</strong> public, researchers and
local authorities, little is known about <strong>the</strong> demography and behaviour <strong>of</strong> <strong>the</strong> raven, o<strong>the</strong>r than
recording its presence or absence. By documenting new observations taken over four months
incorporating <strong>the</strong> raven breeding season (August to November), I hereby described in detail <strong>the</strong>
current distribution, abundance and status <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> on Rottnest Island.
3.2 Methods
3.2.1 Field Observations
<strong>Raven</strong> population sizes and territories were assessed by visually or audibly identifying <strong>the</strong>
species, followed by pursuit and observation using binoculars by a single observer. Six
predefined sites (Figure 2.2b <strong>Chapter</strong> 2) and <strong>the</strong> Thompson Bay settlement were surveyed daily
for one hour per day over three days during each three monthly survey period (September,
October, November 2010) and a follow up survey in August 2011. At least one morning, one
midday and one afternoon visit were made to each site during each trip to avoid bias <strong>of</strong>
observing <strong>the</strong> same site at <strong>the</strong> same time. Opportunistic observations were noted between
sites at o<strong>the</strong>r locations. Individual ravens were noted each time <strong>the</strong>y entered <strong>the</strong> site
(frequency), <strong>the</strong>ir behaviour (i.e. foraging, perched, flying overhead) and <strong>the</strong> direction that <strong>the</strong>y
entered or departed a site. Notes were made <strong>of</strong> o<strong>the</strong>r ravens audible in <strong>the</strong> area but not
occurring on site. Interactions between ravens and o<strong>the</strong>r avian species were also noted,
including predation and any indication <strong>of</strong> breeding (i.e. pair bonding, nest building, mating).
Locations <strong>of</strong> observations were marked using a GPS and <strong>the</strong> latitude and longitude recorded
into a notebook. The data were imported into GIS s<strong>of</strong>tware Arcview 9.3 for Windows (ESRI
Australia Pty. Ltd.) for mapping and analysis.
3.2.2 Laboratory analysis
The demography <strong>of</strong> <strong>the</strong> <strong>Australian</strong> <strong>Raven</strong> population on Rottnest Island was investigated by
laboratory examination and dissection <strong>of</strong> specimens. Carcasses were obtained from authorised
culling by Rottnest Island Authority Rangers in 2010 and 2011. <strong>Raven</strong>s were trapped from
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