Peter, below, sort of invited me to describe the data from Canberra so I might
as well. The easiest way is simply to copy the main text from my book:
"Canberra Birds: A Report on the first 21 years of the Garden Bird Survey". In
doing so I think it safe to say there is more mentions of this species than any
other except the Common Starling. The info from Brisbane and Canberra is
certainly similar. Here is the main text entry (only) about this species,
obviously you need the book to get the full context of this information:
Pied Currawong Strepera graculina
This species is primarily a forest inhabitant but it has done very well in the
suburban and even urban environment. It has shown an interesting pattern. Its
monthly pattern has changed, yet when looking at the statistics compiled on an
annual basis, this fact is almost hidden. Allison (1993) used the statistics
then available from the COG ABR on the Pied Currawong and a selection of small
bird species, to explore whether there was any evidence of increase in the Pied
Currawong population or evidence of adverse impact of this expected increase,
on other species. The conclusion was negative in both aspects but unfortunately
this well-intentioned analysis missed the point. The data he used were only for
nine years, the ABR contain errors, are inconsistent in method and are
superseded by this report. Also he did not have access to the GBS data now
available nor fully understand what he had. He did not appreciate that to
answer the question posed, requires an examination of changing abundance of
this species over the summer period, the breeding season, not the year as a
whole. Even though overall the numbers have stayed within the same range and
the annual numbers still show a smooth cyclic pattern, it is the steady
increase in summer numbers that has the greatest impact on other birds.
The Pied Currawong was historically characterised by very obvious peaks in
winter when they formed large flocks, with marked drop-offs for summer, when
most left the area to go into the high country to breed. GBS data averaged over
all years shows a low from October to February, rising smoothly to July then
declining smoothly to the November minimum. Over the years the amplitude of the
variation of this pattern has reduced enormously (see extra graph). There is a
possibility that the change in the chart instructions from that on versions 1 &
2 that allowed for recording birds "outside your area" to that on versions 3, 4
& 5 that did not, could have been partly responsible for this. An examination
of the changing average group size over the 252 months of the survey shows that
the size of winter flocks have progressively become much smaller and the number
of birds per observation over the summer have increased. It is unclear why the
winter abundance and group size has reduced so much. Maybe the same number of
birds are now more dispersed through the suburban habitat. Perhaps the fact
that the species is now virtually a resident allows individual birds to
maintain territories which may reduce the size or dominance of migratory
flocks. The birds' behaviour has changed to maintaining social groups and
breeding pairs through the summer. As for abundance, the summer minimums have
steadily and smoothly increased to more than double over that period.
Consequently only in recent years the species has become a very common urban
breeder, (from 17% of records in Year 1 to 60% of records in Year 18). This
increase was gradual. It is very likely that this will have a significant
impact on the breeding of other birds. The impact of this species on others is
a subject for concern or analysis, see Lenz (1990a), Allison (1993) and Bayly &
Blumstein (2001). Major et al. (1996) provided a clever demonstration of its
predation on nests, using artificial birds' nests. Much of the observed
predation is directed towards Common Starlings and Common Blackbirds.
In recent years there have been more breeding records by this species than any
other. Nest building commences in July, peaks in August and is finished by
November. Nests with eggs or young commence in August, peaks in October and is
finished by January, first dependent young in September peaking in December and
last in May. There are many records that appear to show a complete breeding
event and the duration is generally close to 15 weeks.
Graphs on pages: 90 and 103, Rank: 3, Breeding Rank: 2, Breeding graph on page:
107, A = 4.02837, F = 98.70%, W = 52.0, R = 79.317%, G = 5.08.
End of quote
Philip
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