to Revisit Views About Monarch Migration?
by Andy Davis and Sonia Altizer
First, however, we must always consider how Journey North data is collected. To what extent are we seeing changes in reporting frequency by the observers, and to what extent are we actually seeing changes in monarch behavior?
Even with "effort" in mind, however, it still seems very likely that two key factors could have affected the numbers of monarch winter sightings. These observations point to human activities that may be causing changes in monarch behavior:
1) One relates to climate. Given the milder winter climates we’ve had recently, monarchs could survive longer and even reproduce in areas along the coast. Even though monarchs cannot withstand prolonged freezing temperatures, they appear to survive occasional bouts of freezing or near-freezing temperatures for short periods. Therefore, it’s possible that some migrants flew to coastal sites in the fall and remained for the winter for an extended stay.
2) A second factor relates to the planting of tropical milkweeds, especially bloodflower (Asclepias curassavica). Although almost all native milkweeds in the eastern U.S. are perennials that die back in the fall, tropical milkweeds can persist in gardens up through a hard frost. The combination of milder climates and the presence of tropical milkweeds could provide conditions suitable for monarch breeding during the winter months, as occurs in South Florida and much of the new world tropics – and as has been reported in parts of TX during the winter months.
to Reconsider Traditional Views?
Did the Monarchs Get There?
North participants can contribute more pieces to this puzzle of coastal
winter sightings of monarchs, and how this relates to planting of tropical
milkweeds, climate variation, or changes in reporting frequency.
Education Standards >>
Location of Monarchs
January 2006 much warmer than normal >>
Tagged in September, 2005 and recaptured in March, 2006! >>
|A Subtle Surprise: Look at the East Coast! >>|
How could assumptions interfere with good science? >>
keeps temperatures warmer along the coast to North Carolina
|Early sighting in North Carolina March, 2002 >>|