That's what I was thinking..maybe methane? There's been theories that methane bubbles are the reason for the disturbances in the so called Bermuda triangle.
Tectonic plate shifting exposes massive underground sulfur dioxide bubble? Starts underwater, kills the fish, hits atmosphere, kills the birds.
A plausible explanation that is probably being discussed in backroom MSM briefing rooms, convince the public that its nothing of danger to them.
There is a method, it can be tracked, all roads led to Rome is a good analogy in a case like this.
Meanwhile nobody notices small changes, like maybe a little bit of a magnetic pole shifting? Most certainly something from the X Files.