Yes, it was highly localised, and the earthquake caused landslides right in the habitat where the foodplant grew. Whatever the precise causes, it was seen the year before the earthquake, but not a single specimen has been seen since.
Gentlemen, I pose this scenario as a "food for thought" question of our scientific minded members... Let's say somehow the species re-establishes itself (in time); or that despite it's apparent (absence of late) a small colony is discovered. Would either of these newly discovered specimens still be regarded as legitimate "sylvina" ?
If this University professor is the foremost authority on this subspecies (in his homeland); and he is convinced it has gone extinct then what is to be said should anything be found in the future.
Would singular specimens be considered simply "strays" with no legitimate subspecies status?
Would any localized colony merely be considered a "transient colony" likely started up by a stray female so therefore they are not legitimate sylvina ?
And should any colony be discovered down the road would DNA testing be required to legitimize any newly found colonies as indeed sylvina ?
I know that questions like this pose a challenge to someone recognized as the leading authority on something. I don't mean any disrespect. The thing is this butterfly established itself at some point in history and it was long running. It will likely do it again at some point but, maybe not the exact location.
So, are we to believe that one individuals last word that a subspecies has gone extinct to the best of his knowledge is the end of the subject.
The University professor is still looking, just in case it has survived somewhere in the mountains. His main speciality is not Papilionidae, but he has written several books on butterflies of Taiwan including Butterfly Fauna of Taiwan. Papilionidae. Vol. I (Hsu, Huang & Liang, 2017) in which the absence of sylvina since the earthquake is discussed. He also discussed this problem with me when he came to visit Chiang Mai a year or so ago.
Ssp. sylvina is very different to mainland Chinese machaon, and if that were to fly across and recolonise the island then the new population could not be treated as sylvina. Of course if true sylvina reappears, then it will still be that subspecies. It is worth noting that ssp. schantungensis occurs on one of the smaller islands to the north of Taiwan, so perhaps that could cross to the main island one day.
Firstly, nobody can categorically state that a taxon is extinct, only that it is probably extinct having not been found for a long time. There are many examples of presumed extinct animals and plants being rediscovered.
Secondly, whilst I don't profess to be an expert on the group in question, to be classified as a subspecies it must be possible to differentiate it from other subspecies, including the one on the adjacent Chinese mainland, otherwise it would not deserve the status. Therefore, if any further specimens were found it should be obvious whether it is indeed sylvina, or a stray or release from another population; these would be the case even if a stray female established a new permanent population.
EDIT: Sorry, I didn't realise that Adam had replied while I was typing this.
Thank you indeed Adam and bobw for sharing your thoughts on this topic. Your explanations were clear and concise. The subspecies is unique in its appearance. With any luck perhaps a relict unknown population may still be found in the future.
I do remember the case of America's very localized Schaus swallowtail found in only a couple of the Upper Florida keys. That subspecies was very nearly (it was said) wiped out by a natural disaster --- hurricane. The habitat was fairly well beat up but, Dr Emmel and some of his students and or colleagues found enough remaining stock to start a captive breeding program. In time new stock was released back into the habitat and it now exists (albeit still localized) but, now under federal protection by law. Dr. Emmel I believe sought federal protection once it was viable to return stock back to the wild. One of the few success stories as of "relative" late involving an insect of any kind.
The Schaus swallowtail was declared extinct in the US a few years ago, and I understand it was subsequently removed from CITES as a result.
Actually hurricanes probably populated the subspecies in Florida Keys, because it is actually native to The Bahamas and every so often establishes itself in the Keys, presumably after specimens get blown there.
About a year ago there was a photographic record of Papilio caiguanabus published in the Lep Soc. News. Presumably that species was also blown to Florida.
I have not heard of this recent development of the extinction of the Schaus but, then I can't keep up with everything that evolves. Do you know if the re-introduction efforts somehow failed? It was said to of been a success story...
I don't want to stray from this thread itself and morph it into another topic but, I am taken aback by such sad news.