Comment on CBN Koel article and Red Wattlebird breeding

["Philip Veerman" <>]

Hi All,

A worthy article on Koel breeding in the latest CBN (and I haven't read it all yet) is seriously damaged by a misleading graph (Figure 2) and bit of text that states (page 98) that "the number of RW breeding records within the GBS sites has also notably increased over the last ten years". I don't have the data for the last six of those ten years but it is instantly obvious at a quick look, that the trend in the graph shown on page 99 of CBN 34(2) for at least the first 21 years (the only years for which the GBS data have been coherently - or competently - analysed) show that the number of RW breeding records within the GBS shows an extremely close relationship to the number of  GBS sites (as is shown in Figure 1 in the GBS Report).  The graph shown in CBN is certainly zero evidence whatever of any increase in RW nesting (even though that may have and probably has increased) because it is a simple count of breeding records and the major part of that trend is the number of people submitting GBS charts for each year. 

The graph as shown is fundamentally nonsensical, which is sad because it is mainly a graph that shows changes in numbers of sites more than anything about the birds. Instead, a graph that takes account of observer participation does make the same point in a reliable manner. If it was a graph of number of breeding records divided by number of sites contributing, the graph would be much smoother and make some sense. See my attached Excel table and graph the data of which are available almost directly from the GBS database queries I set up. It does demonstrate the point they were making. There does appear to be a slight real increase over time but nothing like what their graph shows. It has been a strict and obvious consideration throughout the entire history of the GBS, from year one, that results need to be considered relative to observer numbers (expressed as sites or observer weeks for the year). Having gone to the effort of writing a book that explains how GBS data can be sensibly used, it is "regrettable" to see such logic abandoned in year 27!

Philip

<<...>>

Red Wattlebird breeding trends.xls
Description: MS-Excel spreadsheet

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