Saturday, December 24, 2011

More news from Bungendore

A message to the COG Chatline mentioned hearing a Koel in Bungendore in December.  They came through Carwoola a litlle earlier but have been silent since.

While passing the holding paddocks on Trucking Yard Lane on 22 December we counted 24 Australian Shelduck grazing. A post to the COG Chatline reported 43 Shelduck by the 24th of December.

Thursday, December 15, 2011

Pelicans: slightly out of area

Ellie has reported to me that
"I was driving back to Bungendore from Goulburn, on the Tarago Rd, on Nov 14 or 21 this year at about 4.30PM-5PM when I saw a flock of a couple of hundred pelicans.  They were just past Elmslea and Buckingham Estates and were flying in the direction of Lake George or Lake Bathurst. I know they don't qualify for your bird list in the Gazette but I thought it was interesting."
 It most certainly is an interesting sighting.  I can't recall hearing of a flock of Pelicans of this size in the area around Canberra of interest to COG:
 Presumably it is a result of the inland lakes drying up after a good breeding season.

Although there are no water bodies in the Carwoola area big enough to support such a flock the odd bird may turn up (or be seen flying overhead).

Tuesday, December 6, 2011

The causes of increasing number of species

Following my initial circulation of the monthly report a reader asked:
" ...just wondering what your theory may be on the cause of the increase in number of species seen by month? From this graph it looks like its gone from 60 mto 90 in four years. La Ninya?"
This is a very good question and I shall try to answer it, as far as I can, in what follows.  In so doing I hope to avoid proving the rule stated by a past Australian Statistician:
"If a statistic looks interesting it is probably a processing error."
A primary cause of the increase in the number of species may be an increase in the effort put in.  For the first few months I was more or less the only person contributing to the statistics (which I did because that is the sort of thing I am interested in).   Then an observer in Hoskinstown joined in providing monthly reports, and after another year or so, another observer also began to pass on the records he maintained each month.  I have separated the reports provided under these three scenarios below.

There is clearly a 'jump' following the additional data from the observer in Hoskinstown, but the increase attributable to the observer in Widgiewa Rd is less clear.  Interestingly, using that well known statistical technique "gut feeling" I believe there are a number of species reported on a regular basis from Widgiewa that aren't reported frequently by others (eg Hardhead, Stubble Quail, Eurasian Coot).

Since the series looked rather like an abused cross-cut saw blade I decided to remove the effects of seasonality using a 12 month moving average, centred on the 7th month.  (Details of the calculation available on request.)
This shows that there is a steady increase over time.  If the analysis was looking at the total number of species ever recorded in the area over time, such an increase could be expected as 'unusual' species occur for the first time and are added to the list.  However, an increase in the average of this nature cannot be explained by such a mechanism.  It is particularly puzzling since in 2010 there were very few waterbirds recorded in the area as they had moved to the flooded inland areas to breed.

If there was a 'real' increase in diversity in the area (such as would arise from Climate Change) it could be expected that this would be revealed by the results of the Garden Bird Survey (GBS) undertaken by the Canberra Ornithologists Group.  (This covers all of urban Canberra-Queanbeyan and a scattering of sites in the rural hinterland including my site and one in Hoskinstown.)  However a chart of the number of species recorded each week (raw data and moving average) in the GBS does not show a systematic increase.
My personal GBS site (restricted to 3Ha around our house) shows a small dip in the early weeks followed by a gradual increase in the average number of species recorded for effectively no overall change.
The increase in more recent months probably reflects:
  1. my increasing familiarity with the birds in the area (I think my effort is similar); and/or
  2. the outcome of efforts to regenerate the vegetation on our property.
However it is not sufficient to explain the growth in the overall series.

At the time of publishing this post I conclude that the only remaining source of change is the information provided by other members of the Carwoola Community, who do not record birds on an ongoing basis but advise me of the observations that are of particular interest to them.  My gut feeling is that such reporting has increased, but I do not have any recorded data to support this. This conclusion stresses the importance of a wide range of observations and the great value of ad-hoc reports.

There is some evidence that factors of widespread impact such as climate change are not responsible for the observed increase in the average number of species reported in Carwoola.  Likely causes are seen to be:
  1. An increase in the amount of information reported on a regular basis; 
  2. Efforts to regenerate vegetation has led to a small increase; and
  3. Increased numbers of ad-hoc reports by many members of the community.