Seasonal occurrence, body composition, and migration potential of army cutworm moths in northwest Montana

Grizzly bears (Ursus arctos horribilis) consume adult army cutworm moths (Euxoa auxiliaris) from late June through mid-September on alpine talus slopes in Glacier National Park (GNP), Montana. As part of a study carried out to better understand the ecological interactions between grizzly bears and army cutworm moths in GNP, we studied temporal abundance patterns, body mass and composition, and migration potential of moths collected from alpine moth aggregation sites throughout the summer of 1994 and 1995. Army cutworm moths arrived in the alpine zone of GNP in late June or early July and departed by late August or early September. While moths were in the alpine zone, their body mass and moisture, lipid, and gross energy contents markedly increased and crude protein decreased. The absence of moths from the alpine zone coincided with the presence of moths on the Great Plains. Using published estimates of the cost of transport in flying animals, we calculated that an army cutworm moth flying in late summer through still air could fly 140 km using body lipid reserves alone.