All About Birds: Eastern Bluebird from the Cornell Lab of Orinthology has some great information (including photos and sounds) of this lovely bird. They have a range map that shows bluebirds are seasonal residents of Michigan, preferring to head south in wintertime. You can also see the UM Animal Diversity Web’s Eastern Bluebird (Sialia sialis) and the Wikipedia Eastern Bluebird.
The Michigan Bluebird Society says that:
Back in the 1700’s when the eastern U.S. was getting populated, indications are that bluebirds were more common than they are now. As more and more farmland was created, bluebird numbers almost certainly expanded even more. Why? First, more farms meant there was more open habitat which bluebirds love. Second, the early settlers typically planted apple orchards. Apple trees are one tree which easily produces cavities which are perfect for bluebird nests. And third, in building these early farms, settlers would erect fences made of wooden posts from the trees they cleared. These many fenceposts would eventually develop rotted out cavities and woodpecker holes which again, would provide ideal bluebirds nesting sites.
Bluebird numbers are believed to have expanded up until the late 1800’s when two non-native bird species were introduced to the U.S. – the House Sparrow and the Starling. These two aggressive and invasive species quickly spread and out-competed bluebirds for natural nesting sites. In addition, as urban areas expanded in the 1900’s and pesticides started to be used in agriculture in increasing amounts, bluebird numbers declined more quickly.
They and bluebird groups across the country have worked to restore these birds and their numbers have been increasing since the 1970s.