Whistler Reporting Rates

To: <>
Subject: Whistler Reporting Rates
From: "Philip Veerman" <>
Date: Wed, 25 Apr 2012 16:06:48 +1000
Thanks both.
A quick response:
The measure Paul describes as "For the GBS, counting the number of weeks the species was recorded each year, divided by the total number of weeks recorded that year, to arrive at a percentage." This is the R% statistic, as given in every ABR and explained and defined as such in The GBS Report. Assuming of course and I hope that he means the number of observer weeks, not the number of weeks! As the number of weeks is limited to 52 but the number of observer weeks is about 1800 to 3500 per year. It is curious that the data graphs from Paul start in 1990 and not 1981 but maybe just the earlier years don't have non GBS data for the comparison.
Geoffrey comments that these "GBS reporting rates" from Paul are similar on graph to the graphs of the A statistic from The GBS Report. And correctly so, as these are species that are almost always observed as singles or maybe pairs. By definition, if every observation was of one bird (or even any random number, provided it was always the same number), the graphs for R (Recording Rate) & A (Abundance) would be identical in shape (different axis labels if the number was higher). The closer G (Group size) is to one, the more similar the graphs are. Note that G=1.19 for Golden Whistlers (GW) and G=1.21 for Rufous Whistlers (RW), so they are similar and close to one. For most species, the G stat is generally stable over the years). It is abundance and social behaviour of birds that creates the difference. The relationship of the GBS reporting rate and the GBS abundance is discussed in great detail in The GBS Report, esp. pages 31 to 34. That is the single most important item from the whole GBS, in terms of understanding bird surveys.
Yes the drop of GW R% following the fire year is dramatic and then following very dry years. Tempting to make a link there. I wonder. There would have been much habitat loss in the high country and likely lowered forest productivity. It really would be useful to update The GBS Report to see what has happened since.
Remember that broadly speaking, for the GW for GBS years, two years of presence are combined into one data point but for the RW each single year exists as one data point. This is because the GBS year goes from July to June and the GW is in Canberra more in winter yet the RW is in Canberra more in summer. Again this is explained in The GBS Report, pages 29 & 30 & Figure 11 & Table 3.
Geoffrey writes about "a variable not brought out in that table would be the number of sites reporting presence in the same week". That may be interesting. I don't recall that question ever being asked before about any species and I had not thought of that one. The number of sites reporting presence in the same year is routinely provided as the F% statistic and given rather clumsily and inconsistently in recent ABR but this is something else. I suspect that would be a very difficult query to design as to how to answer that one.  
For what it is worth, this year (although there is still the second winter to come) is I believe for the first time ever, that I have reached April with no Golden OR Rufous Whistlers on my GBS chart.
-----Original Message-----From: Geoffrey Dabb [ Sent: Wednesday, 25 April 2012 1:44 PM      To:
Subject: FW: [canberrabirds] Whistler Reporting Rates

Thank you for taking the trouble to do this Paul.  Very interesting.  With no expertise, least of all in mathematics, I am not deterred from offering the following comments.


First, your graph on the GBS reporting rate broadly mirrors Philip’s based on abundance – for the comparable period.  Philip goes back 10 years earlier, but stops at mid-2002.  Your graph for the more recent years might well indicate a reduction in GW numbers in gardens due to the fires (January 2003).  I note from the ABRs that GBS numbers for the GW were –


2001-2002: sites 69.5%, weeks 45

2002-2003: sites 72.4%, weeks 38

2003-2004: sites 73.3%, weeks 52 (post-fires dispersal?)

2005-2006: sites 52.9%, weeks 43

2009-2010: sites 54.55%, weeks 37


Not all that dramatic, but a variable not brought out in that table would be the number of sites reporting presence in the same week, which should be reflected in your reporting rate – and in the abundance figure, since most observations are of a single bird. So one theory would be that since the fires (2003-present) there has been a decline in garden GW numbers that parallels the earlier decline (1987-2001)  in (for whatever reason) RW numbers.  I would be interested in the 2011 figures – and in those for the current year which I feel might well show an upswing if other gardens are like mine.


As to the other surveys, these show, I would say, the RW going along at a 5-10% reporting rate and the GW at a 15-20% rate – both pretty steadily and no doubt with their respective seasonal (and habitat preference) variations.  It does raise a question why the GW should have declined in gardens but not in woodlands ….  



From: Paul Fennell [ Sent: Wednesday, 25 April 2012 12:09 PM      To: 'canberrabirds chatline'
Subject: [canberrabirds] Whistler Reporting Rates


Hello everyone, including whistlers, tweeters, and chirpers!


I have constructed two graphs, one from the GBS data, and one from all non-GBS surveys, showing the reporting rates of both Golden and Rufous Whistlers.


I calculated the reporting rates by:

For the GBS survey, counting the number of weeks the species was recorded each year, divided by the total number of weeks recorded that year, to arrive at a percentage.

For the other surveys, counting the number of data sheets recording the species each year, divided by the total number of sheets recorded that year, to arrive at a percentage.


The two graphs show some interesting ups and downs, including one would suspect, the effect of the bushfires on Rufous Whistlers.  I leave it to you to make further interpretations.






Paul Fennell

Editor Annual Bird Report

COG Databases Manager


026254 1804



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