Tuesday, October 28, 2014

Arizona Monarch Migration to California - Another Piece of the Puzzle

 Jessica Griffiths was conducting a training workshop in Pacific Grove, California to help volunteers learn how to count overwintering monarchs for the annual Thanksgiving Count right around the corner. Every year monarchs along the coast are officially counted during the week of Thanksgiving as a base for year to year comparison of the California overwintering monarch population. For the field portion of their workshop they stepped out to practice counting monarchs already gathering in the area. This is what Jessica shared the next day on the Western Monarch List-serve: "Yesterday at the Pacific Grove Monarch Sanctuary, during a monarch count training workshop, we spotted a tagged monarch with a white circular tag in a big cluster of butterflies on a Monterey Cypress tree. I could tell by looking through binoculars that it was a Southwest Monarch Study tag that started with the letter A, but I couldn't read the actual number.  The excitement in our group was palpable!  After Allison Watson heroically drove back to the Museum and fetched a spotting scope, we determined that it was monarch AG210."

AG210 was tagged on Monday morning, September 22 at 9:22 a.m. at the Canelo Forest Service Administration Area in southeast Arizona. She was a freshly eclosed female spotted in the field feeding deeply on thistle. This is the farthest north in California any of our Arizona monarchs have been ever recovered so far. We estimate AG210 flew 680 miles in 34 days or approximately 20 miles per day. We don't know the migration route of this monarch. We do know that Dr. Fred Urquhart and the Monarch Program both noted that monarchs tend to fly north once they reach the California coast. There is more to learn.

The monarch migration is guided by an internal sun-compensated compass. As they fly, they adjust their flight to the angle of the noon day sun. In the eastern migration, Dr. Chip Taylor of Monarch Watch (pers. comm.) observed that the leading edge of the monarch migration begins in Winnipeg, Ottawa (45.42°N latitude) in Canada when the sun angle is 57° to 56°. Through monitoring monarchs that are tagged when freshly eclosed from milkweed fields in southeastern Arizona and later recovered along the California coast in early September, the Southwest Monarch Study is finding that the migration from southeast Arizona appears to begin earlier. Here is a chart of our recoveries to date from September 7 to November 19. The red Xs are monarchs tagged in southeast Arizona that were later seen along the California coast. The bold red X is AG210 that was just recovered by Jessica with a sun angle at the time of tagging of  58.49°. The blue Xs represent tagged monarchs that flew to Mexico. Sun angle at the time of tagging for all Southwest Monarch Study recoveries range from 66.16° to 39.22°.

So what determines migration destination from Arizona? Is it sun angle or something more? Once again wind direction during the week after tagging may play a role. We will continue to review all these factors.