The
photo was taken at Hoskinstown rather than a Garden Bird Survey (GBS) site, but it shows what we are on about!
There have been many recent posts on the
COG Chatline reporting seeing Superb Parrots in various places around Canberra, including some from people's GBS sites. Since these seemed to be earlier than usual sightings I have examined the GBS database to see what it can tell us. It is important to note that the places where the parrots have been (more) commonly reported to COG in the past (Wallaroo Road, Hall; Mount Rogers, Fraser and the Hawker Ovals ) are not covered by the GBS but I believe this story to be reasonably consistent with the overall spread of the species.
Superb Parrots were reported in Year 1 of the GBS (1981-82) and have been reported in 22 of the 29 years for which data has been processed. However they really kicked off in 2004-05 with sustained increase in reporting since then.
Other than the overall shape of the curves, it is notable that the shape of the line for raw count of the number of birds reported is very similar to that of the curve for A (abundance, in which an adjustment is made for variation in reporting effort). To save effort by this author the rest of this report will consider only the raw counts.
Looking at the location of the reporting sites a relatively high proportion of the Superb parrots have been reported from more rural sites in Murrumbateman and Gundaroo in NSW. As these sites are outside the urban ACT, which is the area covered by the current Chatline debate they will be excluded from the remaining analysis. The Chart below show, for the last 6 years- in which 94% of these birds have been reported - the Total number of birds reported and the number excluding the NSW reports.
The remainder of this post will cover only birds reported in the ACT in the last 6 GBS years since that is both the topic of discussion and covers a very high proportion of total reports.
The reports of Superb Parrots over the last 6 years are concentrated in Belconnen.
Within Belconnen the reports are mainly focussed on sunurbs close to Mount Rogers and Hawker Oval.
The exceptional entry in this table is for Harrison (a suburb in Northern Gungahlin) where the birds overfly - possibly to or from Mulligans Flat. It should also be noted that data from a recently established site in Hawker has not yet been processed (sorry, AO: I'll do an update in January!).
The timing of the birds presence is summarised in the following Chart. Over the past 6 years the birds have been reported at least once in 41 weeks of the year.
Clearly larger numbers of birds are reported from week 46 (beginning 13 November) and peak around Christmas. The numbers then decline very rapidly to week 4 (beginning 22 January). A key question is whether the times of arrival and departure are changing. Since there are a small number of birds in the general area all year I defined the 'real' arrival and departure dates date as the first and last weeks in which 10 or more birds are reported.
Note that the vertical axis is the "number of weeks since 3 July" rather than the traditional GBS Week: this enables presentation of the data in a more intuitive format. Although the number of years in the series is not great it would appear that the numbers are building up earlier. However "clear-off date" is more constant. I will leave it to others to offer explanations of these observations.
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