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. Massive swarms commonly follow the passage of cold fronts.
All Dragonflies: A Food Chain Connection
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.
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.
You're the Scientist
evidence could you give to show
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.
Where Are the Dragonflies Going?
Two different populations of Green Darners live in Canada and the U.S. The RESIDENT population does not migrate. They breed in the north over the summer, and lay their eggs in northern water. 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.
Ornithologist's Answer to Journaling Question
What evidence could you give to show that dragonflies and kestrels migrate together? Frank Nicoletti's graph shows the numbers of kestrels and dragonflies every day in September. Every day with a big number of dragonflies has a big number of kestrels, and every day with a low number of dragonflies has a low number of kestrels. It's easy to see that the graph's peaks and valleys for both species happen on the same days. Scientists say these numbers are correlated.