rarest bird

[informashun]

i go every sunday to a quiz and theres a bloke who always asks tricky questions.
last week it was which is the worlds rarest bird?
are there any abers/twitchers who know the definitive answer please.
id love to wipe the smile off his smug face.

[Cetti]

These are the 50 rarest birds in the world:

http://www.camacdonald.com/birding/rarestbirds .html

There is another website that classes the Californian Condor as officially the rarest.

[gen2]

It could be the parrot known as the Norwegian Blue. It may even be extinct by now as the last one seen was in the late 1960s and that specimen was deceased.

[CrazyWolfman]

Surely all the extinct birds are technically speaking rarer than all the ones that are still alive. After all, 0 is smaller than 1. (Sorry)
Personally I think that it's impossible to say, and therefore an unfair question. After all, a species is becoming extinct about every half-hour so what was the rarest bird when the quiz was written had probably died out by the time it was being answered.

Anyway, what was it he reckoned was the rarest bird?