Wednesday, April 2, 2008

Spring Migration

Nature Watch
April 2, 2008

By Susan Benson,
CNHM, Director of Education

The days are longer, snow is melting, and temperatures are rising. For many of us, though, spring isn’t official until we see the return of our favorite migratory birds. Perhaps yours may be the American robin or the redwinged blackbird, or maybe you scan the thawing waterways for returning mallards, goldeneyes or mergansers. Bird migration has mystified humans for a long time. The Greek philosopher Aristotle believed that redstarts actually changed into robins in the winter. As recently as 200 years ago, it was thought that swallows and other migrants spent the winter in hibernation. Only recently have we begun to understand what migrating birds have been doing and why. We now know that almost the entire planet is criss-crossed by migration routes that lead in all directions, not just north and south. Each year some birds nearly encircle the globe in their travels from winter quarters to summer breeding areas and back again. Some of your human neighbors spend winter in the south, most likely because they prefer warm weather. A bird’s seasonal movements — and for that matter the migratory motivation of many other creatures including insects, fishes and mammals — are not strictly related to the temperature. In fact, most birds are well equipped to survive the cold. Migration is motivated by a search for food. In the fall, many birds depart northern regions in search of more reliable food sources. Come spring, these birds return north with the increasing availability of the tasty insects, fruits or small animals they eat. It might seem that birds would do well to stay in warm regions with plentiful food year-round. They return northward, however, for good reasons. Tropical days are only 12 hours long, but days in the north may reach 16 hours or more — that means more time for gathering food. Northward migration also expands a bird’s available nesting and food gathering area. Some birds do stay in the south, but merely expand their range to the north in summer.

Finally, migration helps protect birds from predation. A predator that relies on a certain bird for its prey will not thrive if that prey regularly leaves for months at a time. We still have much to learn about how birds pull off their amazing migratory journeys. How do they find their way, year after year, on trips that can cover hundreds or thousands of miles? Most researchers agree that birds use a variety of navigational tools, including visual recognition of geographic features like rivers, coastlines and mountain ranges; sensitivity to earth's magnetic field using tiny grains of a mineral called magnetite found in birds’ heads; use of the sun and stars for guidance; and simply by following other birds.

The first birds are already arriving; trumpeter swans were in Pacwawong just north of Seeley on March 17, Canada geese on March 30, and many reports are coming in to the Museum about bald eagles, first robins, and other animal species. Keep your eyes out and upward to make your own observations!

Brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. They invite you to visit their facility in Cable on 43570 Kavanaugh Street or at the website at to learn more about their exhibits and programs.

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