Chad Underwood and Sean Cahill are a couple of others. There's an interview with Underwood about it here:
https://nymag.com/intelligencer/201...o-q-and-a-with-navy-pilot-chad-underwood.html
But it's just more words - there's no actual evidence, these people can say whatever they like. Being retired navy pilots gives them a bigger platform and the media will lap it up, people will simply believe them for that reason alone.
It's also not that outlandish to point out, that these people have all been retired for a while now, it wouldn't take a tremendous stretch to imagine them banding together and cooking up a good story they can sell, would it?
Also, what is he talking about regarding birds?
There are many species of migrating birds such as geese etc, routinely fly as high as 10k-20k feet when migrating.
https://www.livescience.com/55455-how-high-can-birds-fly.html