One answer for Yan

[Kenelm Philip]

	So-called 'hilltopping' is a well-known behavior pattern in some
species of butterflies. Basically, males patrol the hilltop, virgin females
fly uphill, and non-virgin females fly downhill. That much of the pattern
has been verified by field work. The usual assumption is that this is a
mate-locating mechanism for butterflies with low population densities,
whose larval foodplants are widely scattered. Hilltopping allows females
easy access to males (who would otherwise be at low densities). After
mating, the females return to lower elevations and hunt for the foodplant.

	Some arctic species (_Papilio machaon_, _Oeneis alpina_) are
classic examples of this phenomenon.

							Ken Philip
fnkwp at uaf.edu