Monarch flight heights, spring vs. fall

Sheri Moreau sheri at butterflywings.com
Wed Apr 7 15:18:14 EDT 1999


Paul Cherubini wrote:
--------------------snipped--------------------------
If it could be confirmed that spring migrants don't engage in high
altitude (100+ feet), soaring flight, it would mean we could say there
appears to be a fundamental difference in the orientation behavior of
spring migrants vs. fall migrants (more terrestrial than celestial,
perhaps?). That in turn, might help us formulate new ideas about
possible environmental cues (geophysical vs astronomical) spring vs.fall
migrants may use for direction finding and navigation. 
--------------------snipped--------------------------

Hmmm. I always simply presumed that in the autumn they were focussed on
migration to a safe overwintering site, and it's easier (ask any pilot) to
fly at higher altitudes than lower ones (if for no other reason than that
there are fewer obstacles to circumvent).

In the spring/summer, their motivation is completely different.
Reproduction is now the driving force. The females are looking for
milkweed, and the males are looking for females looking for milkweed.
Milkweed is best located close to the ground, not from hundreds of feet up.
It's a simple matter to observe a female criss-crossing a gentle breeze,
5-10 feet up, until she's finally able to zero in on a specific plant
hidden amongst the grasses. Males tend to patrol patches. I wonder how many
overwintered Monarch males find a good milkweed patch in south Texas, with
plenty of passing females, and presto, their northward migration is
finished. They remain in and around that patch until they die (presumably
happy).

Be interesting to know what the percentages of females to males are in the
advancing northward migration, esp. WRT overwintered individuals. Can
someone point me in the direction of a study on this?

Sheri
<sheri at butterflywings.com>
The Butterfly Conservancy, Carmel-by-the-Sea, California
<www.butterflywings.com>


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