According to free range advocate Joel Salatin, the return to free range symbiotic pasturization models for cattle and chickens tend to simulate the prairie grasslands pre 1800s (when buffalo and other ruminates predominated and birds/insects thrived by feeding "behind" them...insects eating their poop and birds eating the insects). This also stabilized/enriched the soils. As such, perhaps future population declines, less dependency on grains & factory farm meat/dairy a partial answer, while fruits/veggies would predominantly be grown in hothouses or aquaponic models, more biodiversity of crops to contain pests and more organic fertilizer (this all worked great for us in our free range and hothouse models). Potatoes (and other tuber crops) a great fit as they can be grown anywhere, and provide starch very cheaply. Of course deforestation must also be devastating for bird populations.