"The fireworks hypothesis is nonsense.

The later Louisiana and Kentucky incidents confirm this."

????

The Louisiana and Kentucky incidents confirm nothing of the sort. Mass deaths of birds is a not uncommon occurrence, there have been at least 90 incidents reported from June to December 12 in the US, according to the U.S. Geological Service. Of these there were five deaths of at least a thousand birds.

I don't find the possibility of the fireworks explanation to be implausible.

First off, the deaths occurred at approximately 11:30 at night when the birds were roosting, so something caused them to take flight.

Second, they have very poor night vision.

Third, people in the vicinity reported hearing the sound of mass wing beats coincident with the discharge of fireworks, some of which were described as cannon crackers which are designed to be extremely loud, not unlike the noise cannons used to keep birds away from airports and crops etc.