California Sister migration is underway (in California)

[Paul Cherubini]

Here at the 1500-2000 foot elevation zone in the Sierra Nevada foothills east of 
Sacramento, California, the annual northward migration of the California Sister butterfly 
is in full swing. Today I could view roughly one butterfly every 3-8 minutes. Stiff head 
or side winds don't seem to blow the butterflies off course - they seem very determined to 
move in N or NNW directions.

The first numbers of Sisters appeared about a week ago. I have seen them moving 
steadily northward for the past 10 consecutive years in the months of either May and June 
(except last year when the species was rare). In September or October each year there is 
also a highly reliable and predictable southward movement.

The strangest thing about our Sister migration is that I have not run into any other 
lepidopterists who have ever noticed this species migrating! So I don't know if the highly 
directional movements I'm seeing occur only in my area or only within a narrow 
altitudinal zone of the Sierra Nevada mountain range. Have others seen Sisters in 
migration in other localities?

Paul Cherubini
Placerville, California