Every year billions of butterflies, dragonflies, moths and other insects migrate across continents, and considerable progress has been made in understanding population-level migratory phenomena. However, little is known about destinations and strategies of individual insects. We attached miniaturized radio transmitters (ca 300mg) to the thoraxes of 14 individual dragonflies (common green darners, Anax junius) and followed them during their autumn migration for up to 12 days, using receiver-equipped Cessna airplanes and ground teams. Green darners exhibited distinct stopover and migration days. On average, they migrated every 2.9±0.3 days, and their average net advance was 58*±11km in 6.1±0.9 days (11.9±2.8kmd−1) in a generally southward direction (186±52°). They migrated exclusively during the daytime, when wind speeds were less than 25kmh−1, regardless of wind direction, but only after two nights of successively lower temperatures (decrease of 2.1±0.6°C in minimum temperature). The migratory patterns and apparent decision rules of green darners are strikingly similar to those proposed for songbirds, and may represent a general migration strategy for long-distance migration of organisms with high self-propelled flight speeds.*58 km = 36 miles.
Wikelski, M., D. Moskowitz, J. S. Adelman, J. Cochran, D. S. Wilcove, M. L. May. 2006. Simple rules guide dragonfly migration. Biology Letters (early online).
Dragonfly migration, part 2 will be awhile in coming, but I have started writing a post describing what we know about migration in odonata. The use of radio transmitters is obviously promising, but also, if one has to use planes, prohibitively expensive.