Yes there is an element of combined probability of all that happening,
inasmuch as assessing the possible genetic origins of the bird and its
arrival at that point. It is those things that are still undecided (but seem
fair to me). However this does not any longer need to be multiplied by the
probability of being found in WA by a birdwatcher. This is because the
latter event is now a known fact. Unexpected maybe but probability only
exists before the event. Once it has happened, the probability of it
happening (at some other random time), now becomes irrelevant, as that part
is now 100%. Indeed this may have happened with other birds in the past that
were never found by any observer, or more in the future, in which case the
probability of them being found is relevant and can be included in the
calculation. But not this one.
If I win (or don't win) the lottery, the probability of this happening is
irrelevant, after the event. The only relevant probability is would I win
the next one (which until it happens is equally unlikely).
Philip
-----Original Message-----From:
On Behalf Of Stephen
Ambrose
Sent: Friday, 25 January 2013 11:26 AM To: 'Michael Raymakers';
Subject: Re: [Birding-Aus] Lesser
Black-backed Gull
Thanks Michael for that interesting information.
Given that there is overlap in the range of the Kelp (Cape) Gull and
wintering Baltic Gulls (L. f. fuscus), that Nikolas provided evidence that a
Kelp Gull can breed with other species (Kelp Gull x American Herring Gull in
North America), and that there still seems to be a debate about the physical
characteristics of the mystery gull, I reaffirm my hypothesis that the bird
at Broome could be a Baltic x Cape Gull hybrid. For that to be true, it
would mean that a Baltic Gull would have needed to extend its winter stay
along the east coast of southern Africa into the breeding season of the Cape
Gull. There's been strong (cyclonic) winds over the Indian Ocean over the
last couple of weeks, so it's not inconceivable that a Baltic x Cape Gull
hybrid (if one exists) has been blown across from the eastern coastline of
southern African to the Australian coastline.
But I agree with Jeff that the combined probability of all that happening
and then being found in WA by a birdwatcher is extremely slim - but still
possible.
Cheers (from rookie gull watcher),
Stephen
Dr Stephen Ambrose
Principal Ornithologist
Ambrose Ecological Services Pty Ltd
Ryde, NSW
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