I suspect, totally off the cuff, that this is more related to destruction of insect habitat, overuse of pesticides, cats, night time lighting, and a whole slough of other anti-insect man-made problems. Global warming plays a part, no doubt, but my guess would be that it’s not the primary problem. Almost all of the yards around me are insect deserts, and these yards are common across the US urban and suburban regions.

For many decades now, we’ve effectively been waging war on a key part of bird diets.

Edit: also, as mentioned elsewhere, we’ve reforested, but have subsequently lost critical meadowland. And our new forests tend to be more monocrop than the woodlands of old.