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.
Cheers
Paul
Paul Fennell
Editor Annual Bird Report
COG Databases Manager
026254 1804
0407105460
