How can this be a mystery?
An autopsie would tell us the cause of death.
Probably.
IF it's something they test for, as far as a poison or contaminant. Then they still have to go back and locate the source.
Are they testing them for signs of localized methane, carbon monoxide or other gas poisoning from a geological source?
I've never heard of any disease this localized and specific, not to mention quick enough to wipe out an entire flock in the space of a couple hours, but if they exist are they including them in the tests?
How much time and money are they willing to spend? Or does "they all developed blunt force trauma and internal damage by magic in the air and fell to the ground, which did not harm them" work for their budget?
I can guarantee there's a rational, tinfoil free explanation here. Just wish we knew what it was. Still the only common denominator I've been able to find looking at the maps is new natural gas exploration or drilling - for both events in Arkansas, Louisiana, Texas, Tennessee and Kentucky. Haven't looked up the others yet. But if that's the culprit, why the timing? Makes no sense.
There is a logical reason but you and most have been programed to disbelieve and deny it.