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Field Studies You Can Do at Roost Sites
By Dr. Lincoln Brower

There's so much yet to be learned at the temporary roosts (or "bivouacs") that monarchs use during migration. How would a person study a site? What would you do?

I'd pull up a chair, grab a pair of binoculars and just sit and watch! I'd try to stay hour after hour, day after day--as long as the monarchs were there. People can contribute important observations by going with an open mind and documenting what they see. Science is often done with pre-conceived ideas, and so scientists can get hung up on their own theories, and forget to ask "What IS going on here?"

    Hear Dr. Lincoln Brower
Monarchs resting at roost in Minnesota.  
Audio File

A very thorough ethogram (behavioral description) of the dynamics of roost formation during the fall migration needs to be documented and published. It is really amazing how little we know about these critters.

Here are some of the questions I'd try to answer:

  • What time of day do the monarchs arrive?
  • Do they gather up in the sky and all drop down at once?
  • Or do they arrive gradually?
  • How do they interact as the roost site forms?
  • How tall are the trees? Do they afford protection from the wind?
  • Does the roost-size vary, depending on the direction of the wind?
  • Are they active at night? Can you tell when they go to sleep?
  • How long do individuals stay? (To test, tag and release. See: Mark, Release, Recapture)
  • When do they depart? Do they all take off the next morning? Or on the next clear day? Do they gather and wait for the next front to arrive?
  • We know they fatten up as they fly southward, so nectar is important. Can you spot good nectar areas nearby? How do numbers of monarchs nectaring compare to numbers at the roost?
  • Take videos of the butterflies as they are forming their roosts and then take the tapes home and study them carefully. Keep track of the time on the tapes if possible. There is some complex social behavior going on that might emerge through thoughtful observations of the tapes. If you can speed up or slow down the videos when you show them, it could shed even more light on what is actually happening. Early morning videos--as they wake up and fly off--would also be very valuable to study.


Please report your observations to Journey South and help document this interesting aspect of monarch migratory behavior!

Courtesy of K. Wheeler

"Wing-flashing" behavior, seen when a new monarch joins the roost. Video Clip >>

Courtesy of Sheila Daniels


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