White Throated Sparrows are a common bird species on the island. NPS Photo/Paul Brown. 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.