Thursday, September 10, 2009

Fall Migration

Nature Watch
By Susan Benson,
CNHM Director of Education

We may still be hoping for summer, but the birds know better. Migration is peaking for many species, especially broad-wing hawks, Canada geese, and some of our nocturnal migrant warblers, flycatchers, vireos, hummingbirds and orioles. Barred owls and whippoorwills have been calling at night. Red-winged blackbirds and starlings are flocking in larger numbers. Keep your eyes out for these migratory treats.

Broad-wings can be seen passing through, with the right winds, in large numbers. Like most raptors, they are reluctant to cross large bodies of water. When they migrate south and encounter Lake Superior, the birds naturally veer southwest along the lakeshore. Broad-wings migrate at high altitudes and seldom stop to hunt during the days of their travels. Because of their dependence on cold-blooded terrestrial prey species, they migrate all the way to Central and even South America. In order to conserve energy on their long journey, they float upward on vertical air currents as high as they can go, and then shoot forward, coasting to the next thermal. These air currents, called thermals or updrafts, often are found above rock outcrops, buildings, or parking lots—surfaces that heat the air above them. When one broad-wing discovers a thermal or updraft, others quickly join it, all swirling upward in a “kettle.” Many different raptors use these same techniques for migration flight. However, these are just some of the fall migration clues at which to search for.

Warblers migrate at night in large flocks. As the full moon wanes after Labor Day weekend, look for bird silhouettes against the moon as they migrate. Anyone with a telescope with twenty to thirty times magnification can often see these birds on clear nights while “moonwatching.” Nocturnal migrants typically are birds that have longer distances to fly. Less wind allows for straight flight, so birds expend less energy correcting or maintaining their course in the air. Cooler nights provide benefits as nocturnal migrants maintain healthy body temperature without large water losses. The night cover also allows the birds to avoid predation. The right conditions can bring about good bird viewing during the next day.

A clear night with a slight, north wind can bring about good warbler viewing the following morning. During the fall, many males bright, spring breeding plumage has faded, but in spite of their paler reflection, they still have distinctive markings that can help with identification. To look for warblers, focus on mature woods, in clearings or edges of thicker forested areas. Wooded lakeshores also attract fall warbler species. Fall migrating warblers move in waves, in groups of mixed species. If a birder hears the “chick-a-dee-dee-dee” of a chickadee, it is a sign that warblers might be nearby, as chickadees often mix in with warbler groups during fall migration. Finally, knowing a little bit about their habitat can aid with identification. A bird foraging at eye-level could be a black-throated blue warbler, or a bird moving up and down a tree like a woodpecker could be a black-and-white warbler. Using these techniques makes it easier to catch a wave of warblers.

Nighthawks can be seen in the evenings in large numbers. These birds can be recognized by their long, thin wings marked with a white crescent near each tip. Adult males can be further identified by their white chin strap and white tail markings. Nighthawks migrate before cold weather settles in so they won't run out of flying insects that fuel their journey south. It’s amazing that these birds never seem to fly into each other as they dart this way and that for their food. They often time their flight with the air travel of flying ants. By mid-September, nighthawks will be gone from our area, and by late October they will be in South America.

Become a phenologist! Mark your calendar each day you see a change in the transition from summer to fall. After many years of recording, you can take pleasure in knowing when to expect an event in nature to happen.

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. The Museum invites you to visit its facility and exhibits, the Curiosity Center and Brain Teasers 2, in Cable at 13470 County Highway M. Also find us on the web at to learn more about exhibits and programs.

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