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Hi Chris,
I am pleased that you
thought that might be the case. However I disagree with your points as
below:
All available data must be used.
Not only because it should be, but because if it isn't, then the question will
be asked as to why not. Then we will look silly, especially as it is COG's data.
However it should be used properly and any biases involved (which surely do
exist) should be understood, explained and included. As I
have indicated, the non decline shown from GBS data could easily be consistent
with a decline in breeding activity.
I don't agree that
"in the case of this particular species the only data that can be used for the
nomination is the decline in breeding." This is because the numbers are so low.
Correct me if I'm wrong. I think it something like two or three or something
like that known nests. That is nowhere near enough evidence to be statistically
valid proof of anything. It could be random sampling effects. It is like soccer.
I don't believe a 1 - 0 score indicates that one team is any better than the
other. The GBS data is a vastly greater sample size of data, that is continuous,
compared with a few years widely separated data by a small number of people,
collected in an variable manner (between years) albeit with a much more
targeted approach. I can't see that the evidence as presented proves a
consistent, biologically meaningful decline of breeding of the species. Not
that it may not be the case.
Why
should we "assume the proportion of ?new? bird observers has increased"? Where
is the evidence for that? There isn't any. If you have a look at the early years
GBS participation (and I have proof read every one of them) you certainly don't
get that impression. On the contrary, Figure 4 of the 21 Year GBS Report (not in
the 18 Year Report, as I decided to replace what I had in the first edition to
something much more useful) specifically shows that the level of continuation by
participants to the GBS, from one year to the next, has increased drastically,
over the 21 year duration. Thus the proportion of ?new? bird observers has
declined significantly (not increased at all).
If we wish to hide behind misidentification, then
how do we believe any bird survey data on anything? What is the point of
the Annual Bird Reports or COG meetings or anything else? Where do we draw the
line? You write: "Just because there is more information
about does not necessarily mean that correct identifications will follow." Of
course, but taken the other way, less information about, many years ago,
does hardly suggest that more correct identifications occurred then.
Besides as I have said, because of sample size differences and the fact
that Whistling Kites are more often recorded away from urban areas, even if all
Whistling Kites and Black Kites recorded for the GBS were Little Eagles, or vice
versa, there would be hardly any difference in the conclusions. You wrote: "if we have good reasons to think a large proportion of the
observations are dodgy--- hence back to our problem!" Well pessimism alone is
not a reason. Any argument certainly has a long way to go to prove that and
right now the argument doesn't even have a starting point. We know that the
species occurs here as a breeding resident. It is not a vagrant. There is only
one other moderately common species that is easily confusable and that only in
less than reasonable circumstances, plus several other species that in very bad
circumstances could lead to errors. There is no a priori reason to think that
identifications of the species are more likely to be wrong than right. The GBS
culture had been "if in doubt, leave it out". It may be that a very small
proportion of the observations are dodgy but even more likely that of the actual
Little Eagles seen, that the observers were not confident of the identification
and they were not even recorded at all. That problem should have reduced over
the years and this alone could be a factor contributing to a slight
increase.
Low numbers of the
species and low breeding success is reason enough to nominate the species,
regardless of whether the species is in decline, stable or increasing. The such
trends are is simply too hard to determine. In a species like this however,
Atlas type data can be useful to help with that. I am quite willing to accept
that the species is probably in decline. It makes sense, given that the
Wedge-tailed Eagle is doing so well and there is likely to be negative
interactions between them.
Philip
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