From my experience, there is a usual big flight of American Coppers up there in the second half of September...
Brief survey on the way home from work in the Enosburg priority block. 1 Cabbage white, 2 Monarch, 7 sulphur and 1 Mourning cloak. I needed to voucher the cloak but couldn't net it and didn't have my camera. Also took a short walk around my yard and saw 1 Monarch, 1 Sulphur and 14 American Copper. I have never seen more than 2 American Coppers at a time. Is there any explanation for why I had so many?