As human population numbers have increased in the U.S. and across the world, more and more pressure has been put on America's farm land -- the source of 15% of the world's cereal production.
The good news is that record crops are being produced despite the fact that less and less land is being put under the plow.
The bad news is that this increased production has required more automation, less fence-row cover, and more intensive management of farm habitat than ever before.
A good example of what is going on can be seen by taking a look at America's hayfields. While 40 years ago a hay field might have been harvested once a year, most hayfields are cut three times a year now, thanks to automation. The second and third hay harvests typically occur just as grassland birds are breeding. The result -- a tremendous decline in grassland breeding birds across the U.S. (PDF at link)
The number of hayfields in the U.S. is also in decline -- a direct consequence of fewer horses and fewer grass-fed beef cattle, and also a decline in grass-fed dairy production.
Today most cattle are fed and fattened on grain, which produces both greater milk yields and more rapid beef production. While consumers benefit, grassland bird populations are in general and rapid decline.