Monarch Butterfly Migration Update: May 6, 1997
The monarch migration pushes on! Another 25 new sightings were reported this week, including the first from Nebraska. Also for the first time, many observers are beginning to notice monarchs with fresh wings. This means butterflies of the new spring generation are now on the wing; presumably these fresh butterflies are not migrants from Mexico. Here's an example from Virginia:
In contrast, read this report from Kansas:
Karen OberhauserConcerns About Early Migration
As mentioned in a previous report, Dr. Lincoln Brower believes this spring's migration began unusually early and is progressing too rapidly. He is concerned that monarchs left Mexico early because the microclimate in their winter sanctuaries has been changed as a result of logging of the pine forests. Supporting his concern are this spring's reports about monarchs laying masses of eggs on the newly emerged milkweed.
"My observations of monarchs returning from Mexico to north central Florida in late March and early April have year after year indicated that females almost never lay more than one or two eggs per oviposition event. I suspect that observations indicate egg dumping by monarchs coming up so early from Mexico that have been unable to find milkweeds."
Dr. Brower wants to document how far north the monarchs from Mexico have traveled this spring, as a way to support his concern about early migration. Right now, he is collecting samples of monarchs from across the U.S. and Canada. Because this spring's migration is unique, and because the monarchs are reproducing quickly, he has only a few weeks to spare.
His research question: Which butterflies are directly from Mexico and which are offspring of the new spring generation (i.e. those produced in the southern states this spring)?
Wing condition is one clue: Monarchs with fresh wings obviously cannot be migrants from Mexico. What about monarchs with faded wings? How can he be sure they are from Mexico? Dr. Brower will take "individual cardenolide fingerprints" of the butterflies he collects. Fingerprints from butterflies?!
Here they are!Early Monarch in Massachusetts
As promised, Katie Gengarelly (firstname.lastname@example.org) sent these wings from one of the 2 monarchs she sighted on Cape Cod, Massachusetts in early April. These certainly are monarch wings! (Do you know how to tell the difference between monarch and viceroy butterflies?) As you may recall, this is a very early sighting for Massachusetts. (See chart below.) Look at the migration map and other sightings from early April. Her sighting raises some fascinating questions:
Special thanks to Katie for her careful field observations!
Analyzing Migration Patterns, Year to Year
April Migration Data
March Migration Data