It’s a butterfly behavior
Some butterfly species congregate on hilltops. This is “hilltopping”. The meaning of this behavior has not been exactly teased out. However, it is the current understanding of experts that it tied to finding a mate (Belth 2013).
In the American West there are many hilltops (mountains), in the East not so much. Even in a state like Illinois, which is relatively flat, some butterflies find hills in the landscape to gather on (Jeffords, Post and Wiker 2014). The authors note that species of the Pieridae (White family) are known for hilltopping even in Illinois. So too are Swallowtail and Checkerspot butterflies on a national basis.
Waterworks Hill, field trip destination
My objective in going to Waterworks Hill (Missoula, Montana) today was photographing wildflowers. It is a south facing hill that has a cushion plant community on the ridge line along with commoner grassland species on the slopes.
As I climbed the trail I started to check off flowers: Bonneville Shootingstar, Large-fruit Desert-Parsley, Yellowbells, Nineleaf Biscuitroot. On the lowest part of the ridge line there were a few of the bright pink Mountain Douglasia in flower, the icon for this cushion plant community. Decided to advance up the trail for perhaps better photo opportunities.
With the climb came a couple of new wildflower species: Western Wallflower, Missoula Phlox and a small rockcress that I believe is Lyall’s Rockcress. As I was crouched down at the hilltop getting a macro photo of the rockcress a white butterfly caught my eye.
Encountered hilltopping in action
I followed it in flight and saw it land. Quickly got my second camera in hand and shot several photos. From the photos could immediately say it was a “White” and not a “Marble” butterfly species. Thereafter, saw about six or so twirling, interacting with each other just on the hilltop. Managed to get some photos of the butterflies in flight (photos at top of this post). Also got one perched on the ground.
My own hilltopping found “hilltopping” behavior by a butterfly. Quite an outcome for a simple photography objective. Check out your local high spot for unexpected butterfly action!
