For over a century people have been watching and documenting the birds of Isle Royale. Historical reports from the early and mid-1900s revealed which species were migrating northward, which were spending the summer raising a family, and which were present on the island all year long. Efforts in recent years have included surveys along eight sections of park trails, listening for the songs that birds use to advertise themselves to prospective mates and defend a territory against rivals. Listening to bird song is a fairly simple way to identify birds without disturbing them, and changes in species communities over time can be an indicator of habitat change.
The changes in species lists over the past 100 years tells us that habitats have indeed been fluctuating, sometimes due to human actions, such as fires set to reveal copper veins, but often due to the natural progression of forest and wetland vegetation. After a large fire in 1936, many bird species that enjoy post-fire conditions must have done well. One such species was the Sharp-tailed Grouse, which had been considered a common year-round resident until the past couple of decades when forests again entered a more mature stage. In contrast, Sandhill Cranes have become a somewhat common species in drained wetlands, and in recent years many breeding pairs have been found across the island.