In the United States, deforestation has been more than offset by reforestation between 1990 and 2010. The nation added 7,687,000 hectares (18,995,000 acres) of forested land during that period. A third of the US is now forested, about the same as in the early 20th century. - Andrea Becker/Seattle PI, “Rates of Deforestation & Reforestation in the U.S.”
...our results indicated a role of increased accipiter [hawk] populations in driving Red-headed Woodpecker declines through increased predation. We also found evidence for significant effects of warmer winter temperatures and increased forest cover, both directly and indirectly through their effects on enhancing accipiter populations. - Koenig, Walters, et al. (2017). "Testing alternative hypotheses for the cause of population declines: The case of the Red-headed Woodpecker"
At the local scale, species richness peaked at intermediate levels of shrub cover. Bird species composition showed high turnover along the gradient, suggesting that widespread shrub encroachment is likely to lead to the loss of certain species with a concomitant decline in bird species richness at the landscape scale. - Sirami et al (2009), “The impact of shrub encroachment on savanna bird diversity from local to regional scale”
Here’s the thing: yeah, what with pesticides, fertilizer run-off, and habitat encroachment, farmers haven't done birds any favors - but that's not the whole story of declining bird populations. Nature will not simply revert back to some pristine state if we give back what we took: sorry - the habitat is yours now - multiply and prosper! The landscape is forever changed. If we want to save endangered species, we have to manage the transfer.
Grassland birds generally don't thrive in woodlands. Sometimes, the trees (and shrubs) must go.