Unchecked forest succession is causing increased tree and shrub density in the patchy montane forests of Jasper National Park. I determined the interacting effects of forest density and butterfly life history attributes on the behaviour of two groups of montane butterflies: open area specialists, and habitat generalists.

Butterfly counts and vegetation surveys revealed that the abundance of open area specialist butterflies decreased sharply with increasing forest density, despite the presence of nectar plants and larval host plants in forests. Simpson's diversity index was highest in open, patchy forest. Both open area butterflies and forest-tolerant generalists were absent from dense forest, indicating a forest density threshold above which forest is non-habitat for butterflies. An increase in forest density also caused a decrease in the rate at which individuals crossed the meadow-forest boundary. This response was more pronounced for open area specialists. Within forest patches, butterflies preferred to move through open sections. Open area specialists moved through the forest more slowly. Both butterfly types tended to show rapid vertical flight, or "escape" behaviour, in dense forest.

This study is one of the first to compare individual butterfly movement behaviour among multiple species. These findings provide insight into the possible responses of butterflies to changing landscape structure, and the potential for managing fine-scale habitat structure for butterflies.