Migration! It's not Just for Birds & Butterflies
When you think of migration, most individuals think of birds and butterflies making arduous journeys to warmer places with abundant food. Many are amazed to hear that migration also encompasses species of whales, fish, bats, sea turtles, and surprisingly, dragonflies. The migratory behavior of dragonflies is something that has been documented since the 1880's. However, as with most migration phenomena, the process is poorly understood including what prompts migration, its southernmost reach, and the paths taken to arrive at wintering grounds.
The Common Green Darner, a large-bodied dragonfly species found at Rye Nature Center, has a particularly interesting migration pattern that takes place twice-yearly. Common Green Darners arrive in Rye during the spring to mate, lay eggs, and perish. After becoming adults, Common Green Darners only live for a matter of weeks. Once their eggs develop and hatch, larvae known as nymphs will mature over the course of two to three months in bodies of water. In August, the nymphs emerge as the familiar-looking adult stage and these dragonflies will make the journey southward to mate, lay eggs, and perish. Just like their parents, their migration will only be one direction. It will be their offspring, born on the winter grounds, that will arrive in Rye the following spring.
However, this species has an interesting division; migrant and resident populations. Some eggs are laid in late August, and while the winter doesn't allow for any adult survival, these eggs can hatch and grow as quickly as possible, going through several development stages. By the time winter and cold temperatures come, the nymphs can withstand the harsh conditions and overwinter. When the weather warms, these individuals will finish metamorphosing, appearing the following August as delicate, newly-emerged adults known as tenerals. All told, the development process for residential Common Green Darners can take 11 months!
An American Kestrel enjoying a dragonfly snack!
Frank Nicoletti, a professional hawk-counter at Hawk Ridge Nature Reserve in Minnesota along Lake Superior, noticed that the timing of American Kestrel migration often overlapped with that of the Green Darner during the month of September. In 1995, Nicoletti recorded the migration numbers of both species. 1,106 kestrels passed through, as well as an impressive 10,330 Green Darners! Based on patterns of movement, kestrels would focus on flying during mid-day and by the afternoon turn their attention to consuming Darners. This kind of information was valuable to those in the ornithology and entomology communities. A partnership between the Hawk Migration Association of North America and the Migratory Dragonfly Partnership has since been formed, allowing more data to be collected, often by citizen scientists!
If you are interested in other species of migratory dragonflies, the Migratory Dragonfly Partnership has a wonderful guide focused on understanding and identifying the species that travel during part of their life cycle. If you would like to watch dragonflies on their journey south, visit locations like Chestnut Ridge Hawk Watch in Mt. Kisco or at State Line Hawk Watch off the Palisades Interstate Parkway. Individuals may be traveling singly, or in large groups.
-Amanda Schuster, Environmental Educator
