I live in Oklahoma, and last year was poor for butterflies. We are in a 3 year drought, and I believe the few hummingbirds and butterflies are related to a decrease in wildflowers. Texas, Kansas for sure is in drought, who knows where else in the states but I do know the corn belt up north was hit hard, too.
Maybe that's why Alberta got more than your usual number. Slim pickings here, so they just kept moving north!