Some past year autumn

I'm not sure when it began,
Chaos ensued, some past year autumn
I can't recall, creatures sprung up from the land
Vile, sickening, air so toxic
Breathing labored, no barricade stopped the fumes from wafting in.
Shrieking cries, deafening to the ear
Last I remembered was a blur of feathers descend
From a escaped crow's flittering wing
I'm not sure if it will end.