The apparent decline of the BDF in the ACT at least is a worrying but also curious phenomenon to an interested non-specialist like me. An obvious observation is habitat destruction.
I see lots of them here because of the reed beds and grasses on the Ginninderra Creek floodplain. Obviously, much of the habitat has been destroyed in urban ACT at least. But the curious question to me is why the DBF in particular is declining relative to
the RBF which occupies the same habitat. Is it simply a difference between the species? Is the RBF more adaptable than the DBF or perhaps a more prolific breeder. (The DFF does not concern me so much. I see it more in woodland shrubs than grasslands and for
all of my life it was always exciting to see one because they were always considered a bit rarer than the other two)
From: Julian Robinson <>
Date: Thursday, 24 January 2019 at 11:01 am
To: chatline <>
Subject: RE: [canberrabirds] are Double-barred Finches declining in the ACT? - Using website data
A reminder that the intention of our website Bird Data pages is to enable people to answer this kind of question easily and accurately themselves. A summary of all the information from our database
is there (and probably provides a better long-term view than ebird at this stage). This is not to suggest we shouldn’t discuss such questions on the chatline, but the website data does provide a good starting point for discussion and does answer many simple
questions.
For those who haven’t used it before, using Double Barred Finch as the example …
- Go to the website / click on Our Birds / Bird Info
- Scroll down the list to find Double Barred Finch (by default the list is sorted alphabetically)
- Click on the icon of a graph in the right hand column
There is a deceptively large amount of information available… two examples relevant to the question being asked:
- Click on Reporting Rates tab. (Reporting Rate is the percentage of all surveys in which DBFs were present). The graph shows reporting
rates since COG started systematic collection of data in the mid-1980s. In this case it is easy to see: a) a long term general decline in reports of DBFs, and b) in the last three years shown (2015 – 2017 reporting years), a particularly large drop in reports.
Without knowing anything about stats you can see a decline in reporting rate from generally about 4% to about 1.3% in the most recent year. We could therefore say that DBFs are about a third as common as they were, or that they have dropped by two-thirds.
The Abundance tab (the average number of DBFs per survey) shows a similar decline.
- Click on Distribution map tab. Underneath are two new tabs showing distribution in latest year and over all years. If you compare the
two you can see that in the last year, DBFs are more restricted in their distribution than they have been historically. This is tricky to draw conclusions from since the “all years” is an aggregate and will naturally cover more territory than any particular
year. What it does suggest is that there isn’t any obvious geographic shift from, say, north to south or rural to urban.
Other info includes breeding data and seasonality/monthly variations.
Comparison with the figures for Red-browed Finch and Diamond Firetail tends to support John’s observations, at least for the RBF. The DFT however is lower (2017) than at any time in our recorded
history and seems to have suffered a precipitous and continuous decline since a strong peak around 2010. It will be interesting to see what the upcoming ABR shows about the 2018 year for all three species, as per Con’s comments.
Julian
Website manager
From: calyptorhynchus [
Sent: Wednesday, 23 January 2019 7:33 AM
To: Canberra Birds
Subject: [canberrabirds] are Double-barred Finches declining in the ACT?
This is a sp I used to see quite a bit without looking for it, but recently I realise I have rarely seen them. I continue to see Red-browed Firetails commonly and Diamond Firetails uncommonly.
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