Saturday, December 6, 2014

A note on Willie Wagtails

After I circulated the November report I received an interesting question by email:
We are experiencing a huge number of Willy Wagtails, which is just delightful. I am wondering of you might know why there seems to be so many this year? I have never had so many pairs before, and haven’t done anything different in the garden to attract them either by design or accident.
This was a salutary lesson to me, not to focus exclusively on the rarities but to also consider the common birds!  My answer to the question (is to suggest that it has been a good breeding season for the species with some sites available near the garden in question. It has been very good that I have been stimulated to gather together what I can about Willie Wagtails and to present it here.

They are indeed common birds.  In the first Atlas of Australian Birds they were the second most frequently recorded bird (after Australian Magpie),  Apart from Tasmania (hardly recorded at all) and the big sandy bit in the middle of the country, they were commonly reported everywhere.

COG Garden Bird Survey

In the Canberra Ornithologists Group Garden Bird Survey (GBS) in 2012-13 they were quite common, ranked 47th out of 170 species in terms of abundance.  This has showed somewhat of a boom and bust pattern when plotting the average number of birds seen per active survey week (denoted A).
It is tempting to say the upturn at the end is recovery from drought, but that doesn't explain the big drop and recovery in the first third of the period. 

Willie Wagtails were rated 27th, in 2012-13 in terms of frequency of sighting (a measure more closely related to the Atlas statistic).  In broad terms the pattern over the years is a little more stable than for Abundance, but of a similar overall shape.
This difference reflects them usually appearing in ones and two's unlike other birds (such as Sulphur-crested Cockatoos and Starlings which form huge flocks).  Looking over the first 30 years of the GBS - because I have the basic data for that period - 75% of records are of a single bird and a further 20% are of two birds.  The average Group size in the GBS displays a broadly parabolic shape over the 30 year period(although the R<sup>2</sup> is not significant).
Again I can't explain the shape of the graph, especially the steep rise from 2002 -05.  Possibly it is something to do with the mix of areas in the Survey - I shall investigate this in more detail later.

The final element of the GBS of potential interest is the timing of breeding.  In the following chart I have omitted the weeks around Christmas as there are few reports and this distorts the picture.
This shows that late November - early December is peak time for dependent young in the GBS area.   Carwoola is likely to be a little later than that, but I'd hazard a guess that one or two families have bred near the garden of interest and all the chicks and their parents are currently doing a job on the insects.

By coincidence when we most recently visited Mallacoota we found a family group of Willies, 2 adults and 3 fledglings.  Note the buff colouring on these two chicks/

Carwoola birds

Someone, somewhere in the Gazette catchment area has reported Willie Wagtail every one of the 93 months since I have been recording birds in the area.  So it is common here as well.  As we don't record abundance, but merely presence I can't show change in numbers.

I have 23 breeding records for the species in the area which show a nice pattern through the year.  I haven't quite worked out how to show this a pattern so text will have to do.
Nest building:         Sept - Oct
Nest with young     Oct - Dec
Dependent young    Dec - Jan

So having young birds around at present is very consistent with my records.