Well, about an hour after I published today’s blog post on the painted lady migration, I received an email response from Royce Bitzer (Iowa State University) which answered some questions I’d sent him earlier in the week. I’d waited for his responses before posting, but finally decided to just go ahead with the information I had.
Dr. Bitzer provided one main piece of information that was different from what I’d originally said in my post, which is that there isn’t any evidence that the big super bloom of wildflowers in California spurred the migration. He was surprised by that, but said that based on reports from the Las Vegas, NV and Albuquerque, NM areas, this year’s high numbers of migrating butterflies likely came from places near those reports, rather than from further west in California.
A little bit of additional information from Dr. Bitzer… There is no evidence that painted ladies (or red admiral butterflies) can overwinter around here, so the butterflies we see during the summer get here through migration. The painted ladies in my backyard now are likely a combination of butterflies that hatched out here (descendants of migrants) and others that are passing through from further north. He’s been trying to track reports of movement over the last several weeks, and it appears that the big southern migration started over Labor Day weekend (Sept 2-4) when a cold front swept butterflies out of Canada and into the Dakotas. Since then they’ve been moving further south, reaching Iowa and Nebraska. They are joining up with already-present large populations that had hatched out here before the migrants arrived.
Anyway, I apologize for a second post on this topic, but I wanted to be sure I was providing the best information I could. The original post has now been edited to make it more correct.