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The issue about "dependent young" derives
from an old discussion between Michael Lenz and I (and some others) about
recording "dy" in the GBS, an issue that I had already covered in passing in my
GBS Reports. We copied this correspondence to Martin who has made use of some of
the ideas.
None of the GBS Chart instructions (for any Chart
version - as listed in my GBS Report), mention that to record "DY", they needed
to have been hatched within the geographic limits of the site. It is now
clear that people have differed in their interpretation of the "dy" procedure. I
believe that Michael believes that as "DY" is a subset of breeding records, the
breeding also needed to have occurred within the geographic limits of the site.
I had not thought of that as a necessity or that others would see it that way. I
believe that if the DY were in the site, then that is enough to record them as
such. The breeding graphs and the text in my 21 Year GBS Report makes it obvious
that I used my interpretation, the complication is that not everyone did. The
statistics in the "Birds of Canberra Gardens" also use the same interpretation,
although of course the issue is not mentioned there.
Collecting data by week on "dy", regardless of
knowledge of location of the actual breeding, (as I reckon often you don't know)
means that we have some information (that we otherwise would not) about timing
of and occurrence of breeding, which I see as useful. For example we have from
"DY" data alone, lots of information about the timing and the steady increase in
breeding of the King-Parrot over the 21 years of GBS data that have been
consistently compiled and analysed. Even though the species has probably never
actually bred within any GBS site. Michael expressed the (entirely defensible)
view that on principle it really should only apply to dy that were born
within the area. I think we have agreed to disagree on this. The issue is
about location, more than functional description. It arises with things like
cockatoos that typically move long distances after fledging. The young are still
dependent but far from where they were hatched. Interpreting it as evidence that
the birds bred nearby (or within the 100 metres for the GBS) is an
entirely different (and difficult) question.
What do other bird surveys do?
Philip
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