Arkansas bird kill caused by lake turnover?
My first suspect would be lake turnover, a massive outgassing similar to the 1986 Lake Nyos incident in Africa. Hot Springs isn't called "hot springs" for nothing. There is vulcanism in the region, including ancient diamond pipe structures similar to those in Nigeria and South Africa.
And Arkansas is contiguous to the New Madrid fault in the Reelfoot region of the Missouri boot heel.
Suddenly, thinking "zebras" when you hear hoofbeats makes a bit of sense. That is, there may have been an eruption of CO2 gas from any one of several likely culprits in Arkansan geology yesterday. If there was, it should have shown up in seismic recordings as a measurable minor earthquake. And any lake turnover should look downright evil, the morning after.