Juvenile male American Kestrel hunting Green Darner by Michael King

Last September, while visiting a hawkwatch in southern Ontario, did you notice hordes of migrating Monarch Butterflies and dragonflies? Green Darners (Anax junius) are large robust dragonflies that follow the shores of Lake Ontario and Lake Erie as they migrate south (Walker, E. 1958. The Odonata of Canada and Alaska. Volume 11. University of Toronto Press, 129-130). This is a similar flight path to that of migrating hawks, but is there any significance to them following the same route? During fall migration, American Kestrels and Merlins eat Green Darners.

In September 1995, at Hawk Ridge, the famous hawkwatch site in Duluth, Minnesota, veteran hawkwatcher, Frank Nicoletti, studied the relationship between hawks and Green Darners (The Loon 68: 216-221, Winter 1996-97). He collected data showing that favourable weather conditions for hawk migration also concentrated large numbers of migrating Green Darners. High counts of American Kestrels and Merlins correlated with high counts of Green Damers. In fact, 88 percent of American Kestrels counted between September and November 1995, migrated during September, coinciding with peak darner migration counts. When the winds shifted, the falcons and darners also shifted to the same flight path.  

During September 1995, Nicoletti graphed the numbers of hawks feeding on Green Darners. As they passed Hawk Ridge, 28 percent of American Kestrels fed on Green Darners, with the percentage increasing from none early in the day to 73 percent in late afternoon. Later in the day, the number of kestrels diminished but there was a dramatic increase in the percentage feeding on Green Darners. There were many more darners in late afternoon.  

In the same study, 14 percent of Merlins hunted and ate darners. Migrating Merlins eat primarily birds, but Green Darners are an important secondary food source. The relationship between Merlins and Green Darners was not as strong as that of American Kestrels and Green Darners.

A few Sharp-shinned Hawks, Peregrine Falcons and three Mississippi Kites also were observed hawking insects.

Nicoletti theorized that Green Darners constitute a major prey item for American Kestrels, and that juvenile kestrels are particularly dependent on this food source. While in the nest, young American Kestrels are fed many insects as part of their diet. After they fledge, they feed primarily on insects. Their inexperience catching birds and small mammals makes them more dependent on an abundance of easy-to-catch darners. Juvenile American Kestrels appear to time their first southward migration to coincide with peak numbers of migrating Green Darners.  

In summary, American Kestrels, especially the juveniles, time their first southward migration to coincide with peak numbers of migrating Green Darners. Are any Ontario hawkwatchers studying Green Darners?

First Published in OFO News Vol. 16 No. 1, Page 12. February 1998