It’s really impossible to say, since many species of birds have not been seen for many years but may still exist in small numbers. Undoubtedly there are a few that are down to the last few individuals, or even last individual, at the moment.
The most recently extinct species that we know about is the Po’o-uli of Hawaii. It is possible a few still survive, but have escaped detection.
The Chatham Islands Black Robin at one point was down to a population of 5 individuals, but has since increased to 250.
Hmm, ok, I have been researching for personal reasons and I am friends with a very quirky ornothologist who mentioned the Black Robin. Mostly jungle/tropicals though huh? I wonder why?
Well the black robin is neither jungle nor tropical.
But there is a good reason why most endangered species are tropical: we’ve already exterminated all the temperate species. Seriously, people have been practising agriculture in temperate Eurasia and Africa for so long that they either exterminated or specifically protected all the vulnerable species thousands of years ago. High levels of agriculture were introduced to much of temperate North America more recently, but the land is so productive that it was already fully exploited by 100 years ago. Once again all the North American species vulnerable to this sort of management were either exterminated or protected half a century ago.
In contrast the tropics have been a backwater for Euroepan influence until very recently, making them refuges for wilflife. However since the 1950s there has been an increased focus on developing the tropics, and this has led to a massive surge in extinctions in the tropics.
It’s really not suprrising that most vulnerbale species are tropical and/or endemic to the “New Lands” like Australiasia. It’s simply because we’ve already exterminated any potentially vulnerable temperate species.
Actually, it’s not really a matter of temperate or tropical. A very large number of species that have gone extinct or are highly endangered are island species. Having evolved in the absence of predators and frequently flightless or poor fliers, they have been decimated by introduced cats, rats, weasels, and so on. Also, Hawaiian birds and others have been affected by introduced avian malaria. And of course, since many islands are small, when they are deforested the endemic species have no place else to go.
The avifaunas of Hawaii and New Zealand, as well as many of the Pacific islands, have been decimated. In fact, this process began even before the arrival of Europeans; Polynesian colonization caused an enormous number of extinctions.
Among islands, there may be a greater number of threatened species in the tropics, but this is more a factor of there being a higher diversity of species in the tropics in general than a difference in extinction rates between the tropics and temperate zone.