are Double-barred Finches declining in the ACT? - Using website data

[Con Boekel <>]

Martin

Thank you. An interesting analysis. There are other consideration that may have a bearing:

1. e-recording has changed the citizen science landscape to a significant degree. However different it may be from recording using the old system, e recording has resulted in a large increase in data, often from people who did not previously report data.

2. there is a long term drying trend consequent to Global Warming. This would almost certainly be having an impact on seed productivity.

3. changes to kangaroo grazing which, I assume, is both more pervasive and heavier in much of the former DBF habitats. In particular, kangaroo grazing may well interrupt seed set and seed fall.

4. composition of the grass layer may be a factor. Grass spp composition is changing all the time. Seed size is an important consideration for some seed eating species.  Phalaris is preferred by RBF, for example. What impact will African Love Grass have?

regards

Con

On 1/24/2019 4:25 PM, Martin Butterfield wrote:

A timely comment by Julian. 

I would add that as well as the charts of reporting rates there is a tab for reporting rate data.   With a small amount of fiddling around I downloaded that to EXCEL to see what it told me.  

A first observation is that the rates for the first 4 years up to and including 1985 looks  to be a mixture of months with very low rates (several of zero) and a few high rates (eg March 1985 = 18.2).  So I excluded them.  I then plotted the rates and got EXCEL to calculate 2 trend lines,  The linear (ie straight line) trend has a nice downwards slope and an r2 of just over 0.5, which is quite strong.  Using a 4th order polynomial to get a better fit shows a steep initial decline, then a leveling out until 2012 and another steep decline until 2017.  As is expected the r2 is somewhat higher at 0.60.

I then looked more closely at the data for 1986 and 1987.  While there are many less months with a  rate of zero there are still a few very high values (eg May 1986 20.7 and July 1986 18.2).  This seems to affect the reliability of the trends: removing those two years gives lines with a similar shape but the values of r2 drop to ~0.4 for the linear trend and ~0.5 for the polynomial.  Thus I am not sure that one can be certain about there being a "trend".  

I note that 1986-87 were the first two years of the ACT Atlas project and wonder if those two years are a result of the flush of enthusiasm for that?  WRT to the recent steep drop off this appears to coincide with my observations of the weather in Carwoola of the beginnings of this drought.  Another factor could be be the degradation of Finch Central at Coppins Crossing to make way for the Such Lovelu Unvegetated  Molonglo development.  (At least it has a good acronym.)

Martin Butterfield

http://franmart.blogspot.com.au/

On Thu, 24 Jan 2019 at 14:41, Julian Robinson <> wrote:

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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John Leonard