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Philip - the title of my recent CBN article, and a
casual read of it should make it clear that it was not a paper on the changes
that occurred within my GBS site, but over a much wider area roughly within a
1-1.5 km radius of my home. In fact 15 of the species discussed in some
detail were rarely observed within my GBS site, if at all. For
another 10 species the article simply mentions that numbers in either my
GBS site and/or in the wider area were greatly decreased, or that the
species was not observed. This is well over half the 39 species in the
more detailed account.
Further, it was never intended to be or planned as
a rigorous and detailed scientific account, but merely was the mainly
result of a series of observations made, lots of them by chance while jogging or
walking dogs. Feedback from a number of members indicates they
enjoyed reading this "chatty" account, which simply documents a number
obvious changes post-fires both in occurrence and particularly in breeding in
the area. Whether this was purely the result of the fires, or more likely
compounded by the drought, is unclear.
Due to the qualitative or at best semi-quantitative
nature of the accounts I did not feel it necessary to quote detailed records
from GBS reports, or indeed to attempt to make statistical comparisons of pre-
and post-fire numbers. Since the bulk of these would only have been
available for my GBS site, having done so would have lead to an unbalanced
article as no comparisons were possible for the wider area covered and the
majority of the species. Certainly pre-fires it was clear that a number of
species which occurred in the surrounding area rarely if ever came into my
garden.
You have to acknowledge that the GBS is just that,
a survey of birds that occur in gardens, which in many cases does not
reflect the birdlife occurring in the public parks and gardens, the nature
parks, lakes, rivers, bushland, forests and the farmland which make up the
ACT. Therefore, any report on the GBS cannot be taken as the final
word on bird occurrences and populations in the ACT.
An article limited to my GBS site would be
possible, though I neither have the time nor the inclination to do one at this
time. I really query the value of attempting to rigorously statistically
compare 21 years of pre-fires data, with one or two years post-fires data when
many of the changes are obvious - the first rule of statistics is (or should be)
if you can see the difference if you eyeball the data, then don't bother about
the stats. Also the crucial first 18 months of data are lacking, I simply
wasn't up to doing it then.
Unfortunately, some of these comments also apply to
the wider ACT. Despite the opportunity presented by the fires gathering
lots of data is of limited value if there are no good pre-fire data with
which to compare them. Acceptable pre-fire data would be largely
limited to those 2 ha sites surveyed during the BA atlas and after.
Jack Holland
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