Con, I am not quite sure what you are measuring when you speak of ‘gaining’. The pattern is for W Cockies to nest at well-known local woodland locations with suitable hollows, and in recent years a few pairs of corellas have done likewise, for example at Callum Brae. That local corella nesting is probably increasing gradually, but I doubt it has reached the point there is serious completion for hollows v. the WC. Those resident birds of either species might occasionally be recorded on GBS charts, particularly if visiting feeders. There is a small localised group of corellas in the Telopea Park/Bowen Park area, probably stable as it seems to contain a consistent admixture of long-billed/hybrids.
Then there are the very large “Winter” flocks of either species, sometimes mixed, that come into the suburbs, often feeding on nature strips or median strips, and being most likely to be recorded on GBS charts. Relative numbers of these might depend on breeding success and what the overall population is doing in other parts of its range. It is these flocks that show most clearly the explosion in Little Corella numbers – like your sighting today. There is a question what relative visiting numbers might say about the relationship between the two species. The _expression_ ’recruiting from outside’ would only make sense if stay-overs were increasing the local resident population of either species, which might be happening, but I don’t know of any measuring of this. GBS figures for, say, November-January might give some idea of what is happening, but I doubt the GBS is the most useful kind of counting for your purposes.
However, I think you know all this and are pursuing some other line of enquiry. While the HANZAB entry for the WC on ‘Movements’ confirms my above summary, I note that the very first line under that heading reads: “Vary. Considered resident (Boekel 1980; …” !!
From: Con Boekel [
Sent: Sunday, 1 April 2012 9:48 AM
To:
Subject: Re: [canberrabirds] Little Corella
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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