Fall's Journey South Update: September 11, 1998
Today's Report Includes:
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Green Darner |
American Kestrel |
Frank Nicoletti is a professional hawk counter and bird-bander. His eyes have seen millions of raptors throughout the world, and his hands have held thousands. He spends every fall beside Lake Superior in Duluth, Minnesota, counting the hawks that fly past Hawk Ridge Nature Reserve.
During hawk migration, Frank noticed that both dragonflies and American Kestrels (our littlest falcon) migrate
during the month of September along Lake Superior. He also noticed that kestrels seemed to migrate more on days
when dragonflies were moving. But he couldn't find anything in the literature explaining this. It turns out that
scientists knew very little about the relationship between dragonflies and hawks. So, in 1995, Frank started counting
dragonfly numbers as well as hawk numbers. He used two mechanical clickers to keep count. For a whole month--over
8 hours a day--he recorded the total number he saw every hour. That September, he counted 1,106 kestrels and an
amazing 10,330 Green Darners migrating past Hawk Ridge.
Frank wrote a scientific paper for "The Loon", an ornithologists' journal. He used his data to show that
kestrel and dragonfly migrations are associated. Here's what he observed: During midday, when migration conditions
are best for both, kestrels don't eat many dragonflies. (Probably because the kestrels are too busy flying!) But
later in the afternoon, when the kestrels are flying low again, the majority of them are seen eating dragonflies.
One of his observations may seem puzzling. How would you explain this?
Challenge Question # 2
"Frank Nicoletti believes MORE dragonflies fly at midday than any other time. However, his count was LOWER at midday than later in the day. How can this be?"
To Respond to Challenge Question # 2 please follow the
instructions at the end of this report.
Enlarge Graph for Printing |
What evidence could you give to show
that dragonflies and kestrels migrate together?
Frank is back counting hawks this fall--but he isn't counting dragonflies anymore. (Counting over ten thousand dragonflies in addition to a hundred thousand hawks is too hard on the eyes!) But he still pays attention to dragonflies. Last weekend, there were thousands flying along the Lake Superior shoreline. And sure enough, there were a lot of kestrels. The best days were September 5, 6, and 7, when Frank counted 104, 349, and 98 kestrels respectively. Which day do you think the most dragonflies were seen? Under what weather conditions do kestrels seem to like to fly?
September 5 |
September 6 |
September 7 |
Going So Soon?
Discussion of Challenge Question #1
Last week, Challenge Question #1 asked why the "fall" migration of the birds now crossing the Gulf of
Mexico began in mid-August. After all, most of us think it's still summer in August. But Lina of Malvern, Iowa
knows better. She replied that some songbirds are migrating now because the days are getting shorter and the birds
are looking for food sources.
Because August IS summer, food is abundant along the migration trail--and the weather is not likely to get cold
enough to threaten tropical birds. What could be a better time for migrating thousands of miles?
You may be able to predict WHEN an animal will migrate if you pay careful attention to what it eats! Kestrels are
traveling today along with one of their favorite foods--and here's another migration that's about to begin:
Photo by Skip Ambrose |
Hawk Migration Hotspots
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