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I live in a smallish town in southern Indiana where I have the luxury of being able to walk to the university campus where I work. Ive found that walking to my lab is a great way to transition between life at home and life at work. Walking serves as a buffer to organize my thoughts and prepare for the day. As a biologist who studies bird migration, I love being able to observe seasonal transitions in the avian community on my daily walk to work.
Spring in Bloomington brings swifts, swallows, wrens, buntings, and many more migratory species from as far away as Argentina. In the fall, after our summer visitors begin their long journey to the south, migratory birds that breed in the boreal forest and tundra of Canada and Alaska, like juncos, white-crowned sparrows, and tree sparrows, arrive in large flocks, escaping the harsh winter conditions of the north. The seasonal changes of the bird community are obvious to anyone who pays attention. Like violets in the spring and turning leaves in the fall, birds mark the passing of the seasons.
Annual migrations result in, among other things, seasonal changes in backyard biodiversity and the movement of billions of tons of animal biomass across oceans and continents. From dragonflies to whales, our planet is teeming with organisms that move with the seasons.
However, until quite recently, our knowledge of animal migration was limited. Just ten years ago, when I was a newly minted graduate student, I was told we would never be able to track most birds throughout their annual cycle. I was told that most birds are just too small, that there would never be a device small enough to observe their migrations in the wild. As an empiricist who is primarily interested in understanding how birds know when to migrate, this news took a while to adjust to.
I started my research career "observing" bird migration in caged animals. Early migration biologists in Germany discovered that captive migratory birds are active at night during migration. By counting the number of nocturnal hops a bird makes during the autumn and spring, we can roughly estimate when they start and stop migration. This observation helped the study of migration grow from...