Meeting Abstract

S1-2.3  Wednesday, Jan. 4  Recent insights from entomological radar studies of high-altitude insect migration CHAPMAN, J.W.; Rothamsted Research, UK

Billions of insects migrate between winter and summer ranges to take advantage of seasonally available breeding resources. To cover the distances required (100s km), many insects rely on wind assistance, and routinely ascend 100s m above the ground to migrate in fast-moving airstreams. Given that wind speeds are typically three to five times faster that the insects’ airspeeds, it was not clear what influence high-flying migrants could exert on their migration direction. To answer this question, I have studied the flight behavior and migration patterns of large nocturnal moths in Europe with specialized entomological radars. Radar observations demonstrated that an ability to select favorably-directed airstreams (i.e. northwards in spring and southwards in fall) was widespread among high-flying migrant Lepidoptera, and thus the migrants gained considerable wind assistance for their seasonal migrations. Furthermore, moths preferentially flew at the altitude of the fastest winds, and partially compensated for small degrees of lateral wind drift away from their seasonally-preferred migration directions. Trajectory simulations show that these flight behaviors result in a 50% increase in mean nightly migration distance compared to passively-transported particles (300 km versus 200 km) and a significant decrease in lateral drift. Comparison of moth migration parameters with those of nocturnal passerine migrants demonstrates that the moths’ highly efficient strategies resulted in them achieving the same travel speeds and directions as birds capable of flying three times faster. The flight strategies employed by migrant moths explain how such small, short-lived and relatively slow-flying species are able to cover such great distances in seasonally-beneficial directions.