Pied Currawongs

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Subject: Pied Currawongs
From: "Philip Veerman" <>
Date: Wed, 11 Apr 2007 18:27:45 +1000
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superseded by this report.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


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