Migration at its most basic is the movement of a group of animals from one place to another – and in most cases back again. In some cases like the red-tailed hawk, partial migration occurs; some members of a species choose to remain in their summer home through winter. Mammals are considered nomadic migrants because they wander from place to place based on the seasons. The American bison was a great example of that; it roamed throughout the Great Plains as the seasons changed.
Although migration is a phenomena common to many creatures – from the lowly and rarely seen mudpuppy who migrates less than a quarter-mile and burrows in lake bottoms, to the elegantly beautiful monarch butterfly whose migration involves several generations along its journey.
It’s our avian friends that capture us when we’re witnessing migration. Here in Wisconsin the Canada goose steals the show as the most recognizable avian migrant. The flying V accompanied by the characteristic call is a sign of hope every spring to winter-weary residents and farmers.
Song-bird migration is a daily topic among rural dwellers, from the robin’s return in spring to the subtle reappearance of meadowlarks and bobolinks. As a grass farmer I worked side by side with those melodic creatures throughout the growing season. The bobolink was a particular favorite. Every year I was surprised when it suddenly disappeared from the fields. Bobolinks are one of the earliest songbirds to leave Wisconsin; they migrate starting in late July, headed for Argentina, Paraguay and Brazil – more than 12,000 miles, one of the longest in the bird world.
The fall exodus of the avian world was one that gave me an empty feeling as I walked the last remaining pastures each growing season on my grass-based dairy farm in eastern Marathon County. A flying V of geese would cross the sky on a southward journey. I’d stand and count the months until mid- April when the same skyward V accompanied by raucous honking would head north. Every year my count from November to April would reveal the stark reality that I spent half my life anticipating spring. Migration is nature’s reminder of the fleeting brevity of the seasons. When the chill rains of early November arrived just when it seemed I needed them most, those fleeting avian partners would be gone – save for the ever-present crow.
The migratory behavior of the common loon is a lonely story. After making its way north in spring a loon nests with another adult. If they are successful in hatching an egg – despite predation from snapping turtles, raccoons and eagles – they work diligently to raise their offspring. Then in late fall the parents leave to begin staging their migration journey. Large groups of loons form what is called a raft, or asylum, on staging lakes in preparation for departure. The offspring are left to themselves to hone their survival skills before setting out to migrate to ocean shorelines. It’s not know what triggers their departure and how they are born with the ability to navigate such a journey.
Exactly how animals find their way when migrating is a scientific mystery. Although science has advanced far since when it was thought birds spent the winter under the mud of lakes, it still hasn’t completely solved the complexities of migration. It’s believed some type of internal compass is involved. Some birds may use the sun as their guide to navigate. A star compass is a nighttime version of a sun compass and has only been witnessed in birds. Scientists have discovered that young birds learn the position of north by observing the pattern of stars around the North Star. Constellations rotate around the North Star but they stay in position relative to one another, allowing birds to migrate. Magnetic compasses are also thought to be used by migrating animals. The complexity of the animal world is a wonder we will likely never fully understand.
Animal migration in the spring is a rebirth accompanied by opening blossoms and unfurling of tight-fisted leaf buds in the maple woodlot. When the grasses of the pasture rise emerald from beneath the leather boots of the cattle herder and the air smells of the rich loamy earth, one of the great mysteries of the animal world is in full swing. Nature’s mysteries humble us and keep us grounded. They evoke stories, poems and folk tales while enriching our lives. Such is the mystery of migration. May the fall seasonal migration give everyone time to ponder nature’s mysteries.