Gang-gang, Ainslie

["Philip Veerman" <>]

Good.

 

Martin's summary of trend for the GGC overall abundance is basically similar, with continuation, of the text and graph in the GBS Report.  

 

I would make an additional suggestion, which is supportive of Martin's comment, from my long involvement with the GBS. I only rarely tried to segregate out certain suburbs (it takes a lot of time to do that analysis, unless Martin has found some different way of doing the calculations, and I can imagine the method to do that). I suggest that taking the GBS results (the "A" value) from any two or other selection of suburbs, presumably at random, for any species at random, and doing a similar graph would come up with a somewhat similar pattern. This is in regard to that the smaller the sample, the wider the randomness in the comparison will be. This is what Martin's graph and comment shows. It is surely simply or at least mainly, related to sample size issues, as Martin says. In regard to: "The abundance of Gang-gangs in Ainslie/Watson varies quite considerably between years (especially in the latter half of the series) for which I have no ready explanation" The most useful related query would be to look at how the sample of sites surveyed in that subset has varied over the years and that might give a good clue.

 

I would further suggest that this principle would probably not apply in a few select cases where species are not evenly distributed. I suggest Satin Bowerbirds in Weston Creek suburbs would show a more even pattern than Satin Bowerbirds in all suburbs and waterbirds in sites adjoining lakes would show a more even pattern than waterbirds in all sites. 

 

In the initial years of GBS analysis, there was little if any consideration given to the location of the data. All data were pooled for calculating the statistics and each year's data bore no connection to any other year's data apart from the summary tables comparing the year to the previous year. Not only that but until I invented that each site and observer be given a constant site identifier (GBS Site number) in 1994 and then started the task to put all these data into one system, there was no means whatever to connect the information at one site on one year to information at the same site on another year, let alone to group this by suburb, etc.

 

 

Philip Veerman

24 Castley Circuit

Kambah  ACT  2902

 

02 - 62314041

-----Original Message-----
From: martin butterfield [
Sent: Saturday, 7 November 2009 9:45 AM
To: Pamela Morris-Kennedy
Cc: Canberra Birds
Subject: Re: [canberrabirds] Gang-gang, Ainslie

G'day Pamela

I have attached a spreadsheet
showing the abundance of Gang-gangs in Ainslie-Watson and the Garden Bird Survey
(GBS) as a whole  for the 27 years for which we have processed the results
of the GBS.  (The 28th Year is still being processed.)  

The
measure 'A' is the average number of birds of a species seen at a site for each
week over a year.  For example in year 1 observers in Ainslie/Watson
reported 203 Gang-gangs over the year, and their sites were 'operational' for
249 weeks, giving a value of A of 0.8153.

I haven't tried to analyse the
chart in any detail, but the following points are quite clear:

• Gang-gangs have been reported from Ainslie/Watson every year that the Survey has been in action;
• The abundance of Gang-gangs in Ainslie/Watson varies quite considerably between years (especially in the latter half of the series) for which I have no ready explanation; and
• The abundance of Gang-gangs in Ainslie/Watson is much more variable than the same measure for the entire sample.  This could simply be due to the small sample in those suburbs.
• For the total series the shape of the graph suggests a wave shape - initial drop, then steady(ish) increase and then the start of a decline in recent years.  The correlation coefficient for a trend is 'reasonable ' at .61.
  

I hope this is of interest to
you.

Regards

Martin Butterfield
GBS Coordinator.

On Sat, Nov 7, 2009 at 9:03 AM, Pamela Morris-Kennedy <> wrote:

I don't often see them.  This could be the same pair seen in Foveaux St Ainslie last week (near Campbell St).
COuld someone more knowledgeable than me say how common / uncommon they are in the Ainslie / Watson area?
Pamela (new to list and awed by others expertise!)