Where Have All The Bluebirds Gone?

I remember seeing flocks of bluebirds in my Grandmother's backyard in Eastern Pennsylvania back in the late 1970's. Unfortunately, their population has decreased significantly since then because their habitats have been reduced drastically by construction, pesticides (that have killed many of the insects they eat) and non-native birds including Starlings and House Sparrows that kick them out of their preferred nesting sites. There is hope, but only if humans lend a hand building nesting boxes for them with the precise specifications they need. I hope to see them reclaim their territory one day and thrive again.