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I
don't know why but my computer would not open Martin's attachment, so I will
just imagine that it would show the A values over the years (which I think I can
accurately do). I think the data would support the comments, with these 2
disagreements. That Cockies
are still a long way in front is surely true, but that truth is simply
where we are in history right now. Difference in total numbers in no way
reduces the strong possibility that the massive increase in the Corella population is contributing to the decline in the Cockatoo population. If the trend continues, the trend
itself may become self sustaining. I'm not saying that is the cause, only that
it is highly likely to be a factor. They compete on all levels. That TV show
about Carnaby's Cockatoo showed that galahs & corellas compete with them
too. I also don't see a need to invoke the suggestion of
recruiting from outside, even though it is possibly
happening (or more likely in the previous dry years). As the trend once started
could occur just as well even if Canberra was an island.
Isn't
it good that someone decided in 1989 to compile the GBS data as the basis for a
report on it...........
Philip
Martin
Looking at those graphs it seems to me
possible to hypothesise that if the later years are the start of a trend, then
the Little Corellas are gaining while Sulphur-cresteds are declining,
relatively. I suppose that one of the variables is how much the Little Corellas
and Sulphur-cresteds are recruiting from outside.
What the graphs do show is
what a wonderful resource long-term data collection by way of the GBS
is.
Con
On 1/04/2012 9:39 AM, martin butterfield wrote:
Con
I think the answer is probably not.
The attached GBS based graph shows that the Corellas have - as you
indicate - made a massive increase in the recent past, but while the Cockies
have a slight downward trend from a high point, they are still a long way in
front. The graph also served to jog my mind about how far Cockies have
increased in the past 30 years.
In Ian Fraser's latest book he wonders
if Corellas will overtake Galahs (the latter having themselves only arrived in
this area in the last ~60 years).
Martin
On Sun, Apr 1, 2012 at 9:00 AM, Con Boekel <> wrote:
This morning a flock of 170 Little Corellas flew over Haig Park
in Turner. It is obvious that Little Corella numbers in Canberra have
climbed over the past quarter of a century - certainly in the Inner North. I
often notice Little Corellas feeding in the same trees as Sulphur-crested
Cockatoos - on the same food.
The question I have is this - are our
Sulphur-crested Cockatoos declining as the Little Corellas
increase?
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