Please supply your reference for the statement that disease killed the passenger pigeons. I would like to have it for future reference, that is, if it is true.

From what I've read. It wasn't disease or shooting that wiped them out but from selling the squab on the markets. Disease and shooting contributed. Google up Passenger pigeon and read about it.
It maybe that the Eurasian Dove is going to replace them. There is more and more of them every year. There is boo-coos of them in my yard every day.
It is hard to imagine the number of PP they tell about in the article.

I've heard quail calling all summer in Collingsworth county. Seen pairs but no young birds until this week. Flushed a hen with about a dozen half grown birds. Going back on Monday. I hope to see more. We've had enough rain that dry land cotton looks pretty good. But it's still dry in our shinnery pasture. Rains have been spotty. Temps have moderated this week. Still hopeful for an improved season.