Like others have stated, I used to be able to scare up all kinds of upland game birds just by walking through a farmer's corn, barley, wheat, or grass/hay fields. This was in the 60's, 70's, & 80's. Also, there were still a great number of hedgerows left on the perimeters of most arable land.
The petrochemical companies, along with the pesticide, herbicide, fungicide, & nematicide companies, convinced 99% of American farmers to cut down every piece of forested, hedgerow grown land, and convert every possible square foot on their acreage into cropland.
All in the name of increased production for the 5 commodity crops traded on the world's stock exchanges.
The chemical companies did not care that by eliminating all that vegetation from the so-called unproductive land, they were creating more problems for the farmer than ever before.
His losses due to predation from insects increased exponentially, causing him to need a greater & greater number of synthetic chemicals in order to obtain the same yields per acre as he was able to obtain before all of the forested land, and hedgerows were converted over to growing crops.
At the same time, the farmer's soil life became almost non-existent. Along with a lack of soil life, the land's humus content was lowered to less than 1.5%, in some extreme cases, to less than 1%. Both of these factors, along with the loss of virtually all beneficial bird life from the farmer's land, meant that harmful insects could prey at will upon a man's crops.
Modern farming practices have led to the loss of the protective borders that used to surround just about every farmer's crop fields. With those losses came the elimination of song birds, & game birds, which were primarily responsible for the eating of harmful insects.
Like others here I believe that the massive drenching of a modern day farmer's crop fields with synthetic fertilizers, and literally dozens of toxic chemicals whose only purpose was to kill something has led to a huge imbalance. An insect species that was perceived to be harmful to commodity crops, or a disease that attacked a particular crop, or a mold//fungus that afflicted certain crops, or weed that competed with the commodity crop, all these things exist, and proliferate because the soil is out of balance, and the crops grown on that soil are weakened as a result of that imbalance. Weakened crops attract diseases, and insect pests.
All of those toxic chemicals have had a profound effect on the thousands of different species of animal life that live in the soil. The effectiveness of all those chemicals has diminished over time, becoming less & less effective with each passing year/decade. Causing the farmer to increase the dosage applications to try and achieve the same results as in the past.
It is my belief that the over usage of toxic chemicals has had a profound effect on what remaining song birds, and upland game birds, that have managed to eek out an existence on what most would consider very inhospitable land.
Couple the drastic reduction, nationwide, of protective borders surrounding crop fields where game birds could find a safe home, with an exponential increase in avian & land-based predators, and you have the perfect storm that has seen the dramatic decline in game birds like pheasant, grouse, quail, and woodcock. There's just no place left for most of the species that we like to hunt to safely live.
Well managed border lands should contain over 150 species of different plants/grasses/broad leafs/molds/fungi/shrubs/bushes/trees/ & wildflowers. Along with dozens & dozens of different insects, animals, and birds.
A teaspoon of truly heathy soil, with a humus/carbon content of over 5%, should contain a greater number of life forms than there are human beings existing on the entire planet.
Without healthy soil there can be no healthy insect, bird, or animal life in, or around that soil.
