For the Birds Radio Program: The Dragonfly Connection
Frank Nicoletti has been teasing out how kestrels capitalize on dragonfly migration to sustain their own journey south.
Now that the hawk-counting season is pretty much over, Hawk Ridge’s official counter, Frank Nicoletti, has been devoting his time to analyzing the count data. This year Frank’s work can hardly be dismissed as just for the birds—since he arrived August 31, he’s been counting dragonflies as well as hawks. Dragonflies are a fitting subject for Frank, since they’re the flying predators of the insect world. And some species of dragonflies are true migrants, using the same flyways as birds. Apparently some of the northern lakes that abound with mosquito and black fly larvae are too cold for too much of the year to make satisfactory nurseries for dragonfly nymphs, but the adult mosquitoes and midges that keep the north woods abuzz all summer are too tempting a food source for dragonflies to ignore, so green darners and probably other species that lay their eggs further south head north for summer food fests.
We watch these migrating dragonflies returning south, fueled by swarms of tiny insects and on mosquitoes during those last warm days of the season. Dragonflies have the most incredible mouth parts, which they fling out at their prey in charmingly bizarre fashion, They, in turn, are eaten by the nighthawks and kestrels which seem to time their own migration to coincide with dragonfly movement.
Ever since I first spent time at Hawk Ridge in 1981, I’ve been struck by how many dragonflies fill the air on some August and especially September days, exactly when kestrels are on the move, too. But it took someone like Frank Nicoletti to actually start quantifying this phenomenon. While other hawk counters are struggling to figure out whether a distant small falcon is a kestrel or a merlin, Frank has not only made that ID but also seen three harriers way way over the hill, picked out the speck of an Osprey a mile away over the lake, and tallied 49 more dragonflies. On September 13 alone, he counted 6400 dragonflies, plus all the hawks flying by, and also managed to keep track of how many falcons were actually eating dragonflies as they cruised past. It turns out that about 1/3 of all September kestrels that wing over Hawk Ridge are dining on dragonflies, and in late afternoon, it’s more like 60 percent. On a day-to-day basis, Frank found that even when conditions seem perfect for hawk movements, there weren’t many kestrels unless there were plenty of dragonflies to sustain them.
Frank was inspired to conduct this dragonfly count as part of the North American Dragonfly Migration Project, which was developed out of Rutgers University. This was just his first year—next year he’ll have lots more experience at identifying dragonflies and keeping track of all this interesting stuff, and we’ll learn a lot more about the complex interactions of life in the sky as our own world-renowned hawk man finally goes buggy.