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Sorry,
I am unsure what the mystery is, but beyond this......
Mark
or anyone is welcome to keep lists of any area they wish. That is all part of
the fun or individuality of bird watching. Though it seems to me a lot of work
to have a yard list separate from doing a GBS Chart and I wonder what useful
things an analysis of the difference would show.
The
GBS Report reveals the following about the reason for the 100 metre idea (pages
9-10). It was not of course my doing but the thoughts of others (Henry Nix
etc). It is my belief that the 100 metre concept was a good one and has
served the GBS very well, even with undoubted unfortunate observer
variation in the way it has been used. The survey I did of all GBS contributors
in 1988, demonstrated differences in the way people measured their area and
how that impacted (amongst other things) in the extent of their species
list.
........
Considerable debate preceded
ultimate agreement on two central issues: recording of maximum numbers only,
rather than a simple presence and basing the GBS area on 100 metres around the
house. Contributors were to note only the maximum numbers observed at any one
time during the week. ...............
This weekly time grid is an important feature of the GBS. It differs from
most other bird survey work, which is typically done in areas away from the
observers’ homes. Generally those results easily apply to discrete time periods
when the observer was at the site for that specific purpose (Davies 1983).
However, the GBS is based on the location where the observer is often present.
People vary in time available at home, so this requires special compensation
methods. It was necessary to set a time scale for observations that is broad and
adaptable. Then to pool the data and divide total birds by the number of
observer-weeks.
The maximum
number of birds is the simplest measure and was designed to indicate what the
area is capable of supporting at that time. The 100 metre radius is an
acknowledgment that birds are mobile and also has the beneficial feature of
removing a strong connection to the immediate features of the observer’s own
garden. It allows a count to relate to how many birds are in the area, rather
than just the birds attracted to particular small features. Although 100 metre
radius gives an area just over 3 hectares, in practice it is actually rather
more, as most observers interpret the 100 metres as from the borders of their
property. It is probably unreasonable to believe that people can count the birds
simultaneously present in any larger area.
Of
course the system is not perfect but with understanding of how it is supposed to
work, it does allow for proper consideration of the results. By using this space
concept for the survey we have been able to obtain information of more species
than if we were more geographically restricted. I don't think that most birds
care where the property fences are. The chances are high that for example that
Mark's prior Koel and Lorikeets, having been as close as he mentions, would have
been within his property at some time within the week, so I question the value
of not including them. Or if Mark was hearing them he would likely not know that
they were just over the fence. I think that if the GBS rules followed the
property boundary rules, we would simply greatly reduce the sample size of
useful information available and Mark has given two perfect examples of this. It
might make for a list for everyone's home property but the GBS data set would be
poorer for it. Also if GBS rules followed the boundary, big yards would have a
much bigger area than small yards and people living in units would probably not
have any GBS space. For better or worse I also perceived from when I came to
Canberra in 1983 that the GBS was also largely promoted as a learning tool,
often for beginners. I perceived that the philosophy was not to get too
dictatorial or up tight in the prescription of rules, for that reason. I think
that too has been a great feature of the survey. It has allowed a larger data
capture net and this has increased the sample size, an increased sample size
reduces the effect of random or observer variations.
A
similar situation exists with the time method of recording birds around the
garden. One long time COG member and long ago editor of CBN, for years
maintained a daily list of birds around his Canberra garden. I have no idea how
long for. That is fine if it gave him some joy but it always seemed sad to me
because as far as I know all that data has never been used for anything
publicly. If it was consistent with GBS style it could have contributed to this
data set and been used.
There
are other surveys around as described and fully referenced in the introductory
section of The GBS Report that try to relate bird populations to
the smaller scale features of individual gardens. In trying to understand the
GBS background, I urge that most of the text hinting at history or
explanation of the GBS in Birds of Canberra Gardens be ignored as demonstrably
wrong and a pathetic attempt at rewriting history.
Philip
Following on from my earlier report of lorikeets near my
house in Kaleen, this morning I had 4 Rainbow Lorikeets feeding in a flowering
Eucalyptus leucoxylon in my front yard. Their calls were not the usual
call I would normally associate with Rainbow Lorikeets until they were chased
out of the tree by one of the local belligerent Red Wattlebirds and then hassled
by a magpie. The call then became the typical piercing screech the bird is
usually recognised by.
Incidentally this is a new bird for my “yard” list as opposed
to the area where I formerly did the garden bird survey – I did record a single
Rainbow Lorikeet in a neighbour’s tree many years ago but not in my yard.
Similarly, I do not count the Pacific Koel that landed in another neighbour’s
yard about 2 metres from my boundary. The yard list and GBS sites ARE two
different areas for recording bird presence. This, I believe, is the question
Tonya Haff was trying to get an answer to. My yard list will be different to my
former GBS site and certainly different to the Kaleen list. I know Viv Pinder
gets birds on her side of Kaleen that I don’t get on mine. It was quite a simple
question really.
Mark
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