Fall's Journey South Update: September 11, 1998

Today's Report Includes:

Counting All Dragonflies

Green Darner
Visit the Digital Dragonfly Museum

American Kestrel
The kestrel's call sounds like "killy killy killy".
Sounds by: Lang Elliott
Stokes Field Guide to Bird Songs

Migrating monarchs are so lovely and welcome that people pay a lot of attention to them. But they're not the only insects that migrate. Millions of dragonflies also make a journey south each fall. Have you ever seen dragonflies migrating? Watch for them and report your sightings!

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.

You're the Scientist

Enlarge Graph for Printing
(Click Image)

Imagine that you're Frank Nicoletti. You've been asked to give a talk at a scientific meeting to explain your findings. Using the numbers from the graph on the left, describe the data you collected on Hawk Ridge in Fall, 1995.

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
104 kestrels

September 6
349 kestrels

September 7
98 kestrels

(Maps produced by Purdue University Weather Processor.)

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

"I want to let you know that we have attached a satellite transmitter to a female peregrine falcon in northern Alberta. She is still around the nest site with 3 flying young. I plan to send a more complete email when she begins to move, but wanted to give you advance notice in case you want to build occasional notices into your Journey South program--particularly the one about the migration of hawk food (otherwise known as songbirds) to the neotropics!"
Geoff Holroyd,
Research Scientist, Canadian Wildlife Service Environment Canada
Edmonton, Alberta

More About Migratory Dragonflies
Two different populations of Green Darners live in Canada and the U.S. The RESIDENT population breeds in the north over the summer. They lay their eggs in northern waters, and the babies, or nymphs, spend the winter in that cold water beneath a thick layer of ice. In spring, they emerge from the water and spend the summer as adults.

The other population of Green Darners is MIGRATORY. They arrive from southern regions each spring to breed in the north. Their young emerge in late summer of that same year, and migrate south during August and September. Apparently the migratory population alternates generations between breeding in the north and breeding in the south, but both groups of this population get to spend the majority of the summer in the land of mosquitoes, and maximize the number of babies they produce.

 Hawk Migration Hotspots
Hawks can migrate anywhere, but the biggest numbers of hawks collect along ridges, rivers, and large lake shores.

How to Respond to Today's Challenge Question # 2

1. Address an e-mail message to: jn-challenge-fall@learner.org
2. In the Subject Line of your message write: Challenge Question # 2
3. In the body of the message, answer today's Challenge Question.

The Next Journey South Update Will Be Posted on September 18, 1998

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