Given the wide geographic scope of dragonfly migration, citizen-science observations are critical to furthering knowledge of this remarkable behavior. Our understanding of the migration phenomenon in dragonflies has advanced as engagement in Migratory Dragonfly Partnership projects soar across North America. Now 1,000-strong, MDP’s volunteer network has helped reveal several insights into the behavior and seasonal movements of migrant dragonflies.
Observations made by volunteers, combined with work by MDP partners at the University of Maryland, the Smithsonian Conservation Biology Institute, and the Vermont Center for Ecostudies using elements (stable isotopes) found in dragonfly wings, has helped to track migrants back to their natal ponds. The study of stable isotopes not only can determine the latitude of origin, but also characterize the timing of annual movements in eastern North America as well as the direction and distance traveled by individual dragonflies.
Unlike other insect migrants such as the monarch butterfly, migratory dragonflies do not overwinter in dense groups. Add in their fast flying skills and difficulty of capture, and this means that traditional mark–recapture studies are problematic for dragonflies. Measuring the ratios of stable hydrogen isotopes in the adult wings and the exuviae (cast-off skin) of the final-stage nymph can be used to determine their north–south movements. These isotopes are present in the water where a dragonfly develops, and remain locked in the wings and exuviae forever afterward.
Using these markers, we now have a clearer picture of the geographic scale of dragonfly migration. Examining stable hydrogen isotope ratios in exuviae helped MDP researchers calibrate a latitudinal “isoscape” map, and assessing the ratio in the wings of captured adults allows us to infer the latitude at which the specimen developed and the direction and distance of its movement as an adult. Furthermore, a latitudinal pattern can be seen between first flight dates of the common green darner in North America. As the map illustrates, first flight dates occur later in the year for northern latitudes, seen as early as February in Florida, but not appearing in Canada until June or July. Through this work, MDP scientists were able to quantify the effect of changing temperatures on flight dates of common green darners — and revealed that they travel an average of 27.5 km (17.1 miles) per day during northbound migration.
First-flight dates collected from citizen-science and isotope data in this study supports the theory that the common green darner undergoes a multi-generational migration during their annual cycle. The spring generation migrates north, breeds, and then dies; the offspring of this generation then make the return trip south and the cycle repeats as the offspring of southbound migrants move north in the spring. Each generation likely travels around 3,000 km (1,850 miles), a similar distance covered by monarch butterflies each autumn in eastern North America. There’s still much more to learn about migration in dragonflies, so as the weather warms, keep your eyes on the skies and report those first-of-the-year dragonflies in your region.
To read in detail about this work and other MDP achievements, download the MDP accomplishments report.
Register to submit your sightings or to add a local pond to the Pond Watch program and contribute your observations on the MDP website. If you are an iPhone user, you can download the Dragonfly ID app to help you identify the dragonflies you see.
