Friday, October 11, 2013

Untangling a Long Distance Monarch Flight

I heard the news first yesterday morning. A monarch wearing a Southwest Monarch Study tag was sighted near Morro Bay, California. Later I discovered that a monarch wearing AD 947 was tagged by Joe Billings on September 15 in Hereford, Arizona. It was spotted in Cayucos, California on October 9 by Paul Cherubini, a flight of approximately 675 miles.

We don't know the flight path, only the two observation points. Typically monarchs on their Fall migration will fly South or Southwest from the Eastern United States. Much is still unknown in the West although some tests were observed with farmed monarchs (captive monarch butterflies bred for sale) that were moved around the Western states and released. However, there were not any controls with wild monarchs nor records of wind direction and weather conditions at the time.

From earlier studies about migrating monarchs we do know that they are very susceptible to winds. Dr. Chip Taylor of Monarch Watch observed, "Our tagging records are full of monarchs that have been pushed off course - one by as much as 800 miles. Remember the posting (D-plex) recently on monarchs from the Dakotas, MN, IA with many pushed to the SE?" Furthermore, studies have also documented that monarchs are resilient and can reorient their flight pattern within a week after they are displaced.

Purple arrow indicates wind direction
While most of the recoveries and sightings from tagging monarchs in Arizona during the Fall migration have been in Mexico, a few were seen in California. Monarch scientists have urged us to check weather patterns and winds in the days shortly after tagging to see if they can reveal a clue. So yesterday that is what I did. You can see from this map that in the first days after this monarch was tagged, winds blew at a good clip from the Southeast to the Northwest facilitating movement in that direction. Monarchs also use thermals to gain altitude to fly and with the warmth of nearby mountains basking in the sun, rising air could have easily facilitated vertical movement that could have made a flying monarch more vulnerable to wind gusts. The National Weather Service also reported a storm in the area that day with winds blowing towards the Northwest. Dr. David James, Associate Professor of Entomology at Washington State University, noted, "Yes wind makes a lot of sense. Once individuals get to a certain point towards the coast, its likely other factors take over, ensuring their final destination is the coast."

The truth of the matter is we just don't know. We do know that this year the seasonal monsoon wind pattern was more entrenched than earlier years until late September. We can't say for certain that the winds blew this monarch to California, but we also can't say given the winds that week, that they didn't.

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