Saturday, 9 April 2016

An update on BirdaDay

It is very close to 100 days since the start of 2016 so it seemed appropriate to consider where I am at with my endeavours for Bird-a-Day 2016.  The main answer is that I am still ticking along.  Bird #99, on 8 April was a Musk Duck seen on the Queanbeyan Water Treatment Pond 3 (aka the Poo Pits).
The bladder under the bill indicates it is a male bird.

As in the past I rate species in two ways.
  • The first is the score on a scale provided by the organisers which runs from 1 (forfeit bins if not seen in the area - eg Australian Magpie) to 7 (Casual/Accidental in area seen this time of year - Paradise Shelduck seen on 2 January).  I call this the BaD score, although it is quite a GooD measure..
  • The second is an index I developed in 2014 when I first started and was something to do with relative frequency with which the bird has been record on eBird for NSW or the ACT.  As most of the NSW reports to eBird come from Sydney, the scores - while less subjective than my ratings for BaD - are a bit biased towards Sydney and nearby areas.  Using the same examples as before Australian Magpie has an Index of 582 while the Paradise Shelduck, being the first ever record in Australia, had an Index value of 0!
My first chart shows the running average of these two ratings over the year.
 After some initial perturbation the usual pattern has emerged with the Index score gradually increasing  and the BaD score gradually declining as I gradually start using the more common birds.
It does of course help to travel and we recently had a few days in Coastal Victoria where none of the birds I used are common in my home area, although a couple of them are resident at Mallcoota (eg I rated Azure Kingfisher as BaD 3 there but it would be a BaD 6 bird here).

I calculated (or at least used the Excel function to calculate) the correlation coefficient for the two series plotted above and it came out at -0.72.  A quite high score supporting the visual conclusion that they move in opposite directions.   Interestingly the correlation is much lower for the original values, causing me to look at the extreme contrary ratings.
  • White-headed Pigeon is now common at Mallacoota, with birds seen every day and a largest flock of 12.  Thus it gets a BaD rating of 2.  However it was not reported often in eBird so only has an Index of 27.
  • Australian Pelican is a very common bird around water features throughout NSW getting a Index rating of 225.  However I had not seen them within 20km of our house in the 9 years we have been living here.  (Others in the area have only reported a couple of flyovers in that period.)   Thus a BaD rating of 6 seemed appropriate when 4 birds turned up in a lagoon.  Here are those 4 birds:
The flock below were at Lake Cargelligo, Central NSW.

Comparing both rating scales for the rounds starting in January 2015 and 2016 is interesting.  First the running average BaD scores.
The two lines are close to parallel - correlation  0.89 - once things settled down (the initial chaos is because in 2015 I saw a BaD 6 bird on 1 January and a BaD 3 on the 2nd, whereas in 2016 it was a BaD 3 on the 1st and a BaD 7 on the 2nd) but in the stable period 2016 is staying above 2015.  This suggests that I am seeing more unusual birds this year which is broadly consistent with having particularly high diversity around our garden this year.

Looking at the running average Index scores next.
The correlation coefficient for the two series is 0.92: very highly correlated.  Again the comparison suggests I am getting less common birds on average this year.  As this measure is not at all influenced by my choosing the score it confirms this hypothesis.

Looking at the array of species I have still to tick off it will not be hard to get into May and early June looks not too difficult.  Whether I'll be able to get to the end of June - when a trip away will make life easy for a while - is another matter!  In 2014 I dropped out on 11 June while last year I did a bit better in getting to 15 June.

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