No citation handy, but I came across a theory that the high levels of anxiety and stress and malaise prevalent in modern urban society is caused in part by the

No citation handy, but I came across a theory that the high levels of anxiety and stress and malaise prevalent in modern urban society is caused in part by the absence of birdsong. Consider our savannah ancestors, for whom the ambient sounds of birds constituted an "all is well" signal; cries of alarm and sudden flight served as an early warning system, and their silence could signal presence of a predator or other threat. It seems plausible to me that city-dwellers, at a primal level, "miss" these sounds in whose presence our systems of perception evolved, resulting in an imbalance and heightened baseline fear and anxiety. Related tangent: "forest bathing" is a noteworthy remedy.