Anecdotally, House Sparrows used to be daily regulars in my Turner
garden and are now something like very rare visitors. The last
significant multiple sighting I can recall involved a Pied Currawong
killing a very young sparrow. Sometimes I really do have mixed feelings
about the PCs.
Con
Philip Veerman wrote:
Thanks Geoffrey,
There is a whole set of literature, mainly in Europe, about the
decline of House Sparrows as shown in urban bird surveys. This has
been discussed before. Although the reasons may of course vary from
those here.
In preparing the information for the GBS Report I did of course look
at all the trends for all the species in the various statistics: A, F,
R, W & G (as explained therein). I decided to concentrate on A for
several reasons:
Abundance is the most useful measure, the one that previous writers of
the ABR had used most often and is what really sets COG's GBS off,
against all those many, less useful surveys that only use some measure
of recording rate or distribution rate in their stats. Also the values
of A, F & R are all related, in that, broadly increases or decreases
in each, will go together. This is mostly statistical consequence. It
was complicated enough to include the graphs of A for long term and
monthly for 120 species. It would have been too much to include graphs
of either or both F & R as well. I didn't want it to be too
statistically complex or cost too much for me to produce (as I was
financing the GBS Report from the largess of the unemployment
benefit.) Actually the stats for F & R don't vary much for most
species. I have commented in the text for a small number of species
when there was something useful to say about these aspects. Examples
that come to mind are the Satin Bowerbird and Common Myna. As for F,
it doesn't take much for a species to be observed just once at a site
in a year. Also some years we only had 43 sites, so one random yes or
no makes for a >2% difference. Also F tended to be very influenced by
just a few sites, eg stats for birds that were only recorded from
sites near water or on the fringes of Canberra were unreasonably
variable, depending on the list of sites for the year.
Another point to note is that you wrote "Given that that is over a
full year". Well yes, potentially but not in practice. Figure 7 (page
26) and surrounding text demonstrates that although the modal number
of weeks per chart is 52, the average number of weeks per chart is
only 40, with a broad spread. I would fully expect that the same trend
has continued after Year 21 (but the data are not assembled on that).
Philip
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