Hobbies and relevant to interpreting all other species trends.

To: <>
Subject: Hobbies and relevant to interpreting all other species trends.
From: "Philip Veerman" <>
Date: Thu, 6 Sep 2012 16:51:06 +1000
Thanks for that.  Good stuff. I was going to ask if you could source a graph pretty much as you have done but you beat me to it. The general annual pattern is supportive of what I wrote before. It seems to suggest a possible change in status but it may be hard to get any significant analysis from that.
There are some issues to be aware of though before trying to take the graph beyond its usefulness. This graph is of general records which includes ad hoc ones, I suspect excluding GBS data, and not based on a set survey method. I mainly used GBS data. I believe the real pattern in the suburbs (sampled by GBS) should in reality be very similar to the real pattern in the wider COG area for this species.
Firstly, that graph shows records for the first 5 years are only a tiny fraction of those for the other groups of 5 years since then. However the GBS data (you only need to look at the front cover of The GBS Report), shows that abundance for the first 5 years is very much higher, than for the years since then. Clearly what has happened is that the species probably was much more common in those early years but in those early years, fewer general records went into the COG system in a way that is still preserved in our current records and thus this graph. The numbers 1986-1990 are surely high because those years we were doing the COG Atlas. Indeed I think the proof is there, that the graph for those 5 years looks very much like the graph printed in the Atlas (3 years included). Other than that there are far more general records in recent years because our technology has improved.
Secondly, is the whole aspect of ad hoc records of a species that is not so rare that all observations go into the formal record. People have a range of biases and they are to: preferentially submit a record because it is at an unusual time of year, these tend to obscure the true trends by highlighting the unusual, or: submit a record because it is at the time of year that the interesting behaviours, such as migration, happen, these tend to artificially exaggerate the true trends, or records have a spike because of special effort surveys such as the Blitz weekend. There could be a lot of that in the big October spike in the last 5 years, coinciding with the Blitz activity (maybe Barbara could comment). Analysing the importance of these biases is so hard it rarely is attempted. All of these make interpreting annual trends difficult.
Thirdly, the demonstration of the annual pattern by this species from my writing and speaking about it, of itself has been a feeder into this process of creating sources of bias into what observations, people decide to put onto the formal record or not.
Lastly, of historical curiosity is that I created the histogram in my 1991 article that first showed this trend in the species, from the tiny graphs in the COG ABR in CBN. This was as far as I know the first use of GBS data in formal national literature outside of COG. In the 1980s and early 1990s monthly abundance histograms for most species recorded in reasonable numbers on the GBS were printed on separate sheets and individually cut out and glued onto the printing proofs, on gaps cleverly created by setting a margin to fit them. (McComas Taylor was the clever person who did most of that work. I know because I did a lot of the editing, cutting and glueing.) I used these tiny printed graphs and measured the height of each monthly bar for those 6 years then available and then used Lotus 1-2-3 to create a composite graph, also allowing for that the size of the printed graphs differed between years. Back then the GBS summary information was not retained from one year to the next, other than what was printed in the ABR. Indeed for years 1 & 2 all calculations were done manually on paper, for years 3 to 10 with limited storage capacity (or maybe for other reasons), running the output routine obliterated the results of the prior year. Because I was only looking at annual patterns and not total abundance over the years, I arbitrarily (and as it became clear years later, wrongly) set the total abundance of the species as equal each year. Knowing what the abundance estimate or even number of records was, in those early years was no easy task, as the system changed in the middle. I believe the absence of these graphs in recent years hugely diminishes the value of the recent ABR in showing results for the CURRENT year.
So it was to a large extent this exercise and this species and what I saw was the potential and clearly the limitations of what existed till then, which only output summary statistics separately by species and by year with no connection of any kind between years, locations etc. that lead me to creating the GBS database. Up till then there was no way of knowing what species had been recorded in the GBS over all the years, comparing any year to another apart from the previous one or even a coherent list of names or addresses of contributors other than for each year separately or anything like that.
So whilst the graph presented is instructive, I would suggest against analysing it beyond its use (with cautions partly raised by another recent sad example - but no more of that here).  
-----Original Message-----
From: wallaces [
Sent: Tuesday, 4 September 2012 7:52 PM
To: Canberra birds
Subject: Re: [canberrabirds] Hobbies

The number observed is a simple sum of the number observed - abundance data by month is not something I have readily available yet.  Attached is the number observed data broken down into 5 year periods which may help with the question of changes in the pattern.
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