I run the site, so flagging that up front.

Method, since the number deserves scrutiny: the dataset is every bird on my site where both dates are documented, the last confirmed record (specimen, photo, recording, accepted sighting, or death of the last captive) and the first formal extinction declaration by a recognised authority. That gives 13 species and subspecies. Median gap 36 years, mean 47.5, range 3 to 124.

Two rules matter for reading it. Where a bird was declared twice (IUCN and later the US delisting in October 2023), the earlier declaration counts; using the US dates would inflate most figures. And the sample is small and weighted toward Hawai'i, so the median describes these birds, not a published constant.

The pattern that seemed most robust to me: the three short gaps are all birds whose last individual was watched dying, e.g. the dusky seaside sparrow in captivity in 1987, declared in 1990. Where the record just stops, nobody can date the stopping, and the declaration takes decades.

Happy to go into the sources or any individual case.

It's interesting to see that some populations which are nearly wiped out due to habitat changes, can adapt to the new conditions and slowly rebuild ... but it leaves questions like if the adaptation was behavioural or physical which allowed it's survival is the bird that survived tending to be its own sub species of what existed.

In Australia, well the north part of Queensland at the very least, since the 80s there's really not been that much funding or an obvious program of population monitoring of whatever native species remain, including birds.

I miss what used to be common bird calls from my youth even though I didn't know which bird species was responsible. I've resolved the mystery for a couple I could recall but one still eludes me. In my parts the high canopy tropical forests have taken a huge toll from the 90s, no real wet season with warm rain, no large storms, (these days it's not uncommon to hear alarm around a storm dropping 3 inches in a couple of hours ... used to have years where they were not uncommon,) a fungus pathogen taking out some trees which may just be down to the trees being stressed more than their evolution allowed for - oh yes, the fact that many summer storms on their westerly approach had started to hesitate on a direct track over the coastal areas might just boil down to the man made heat bubble with open cut coal mining and the large areas as per mining which now have no to little vegetation.