What could explain extreme erratic bird behavior?

It is currently migration for most birds (woodpeckers, bluebirds, sparrows, finches). Territories fall apart and everyone tends for forage together (foraging flocks). Cooperation isn't always the best strategy. You are probably seeing competition between species and individuals for your backyard food. The woodpeckers you are seeing are most likely Northern flickers, a common ground-feeding woodpecker. Chickadees are sedentary and most sparrows are migrants. The chickadees may be defending their resources from the new faces. Also, you are probably seeing many juveniles that may be being bullied. Fall is an interesting time of year because behavior drastically change. Hope this helps!