Subspecies and protection
cherubini at mindspring.com
Sat Oct 14 14:35:08 EDT 2000
Ken Philip wrote:
> As I have mentioned before, there was a fascinating paper
> at the 1986 Lep. Soc. meeting (Ottawa) on the migration of
> western Monarchs, which pointed out that they can be
> trapped by (temporarily) suitable conditions in gullies at
> the foot of desert ranges.
The authors of that paper assumed the butterflies were
"trapped" by the 10,000-11,000 foot mountains surrounding
the Saline Valley. To test this hypothesis, I released about
300 tagged monarchs (caught at the roosts along the California
coast) in the Saline Valley during the first week of November
1991 and a "control" group of 300 outside the valley at
The Inyo mountains south and west of the Saline Valley are
10,000-11,000 feet tall, but the Sierra Nevada mountains
south and west of Bishop are 13,000 - 14,000 feet tall.
Thus, the butterflies released at Bishop had a more
formidable barrier to cross to get back to the California coast.
Within 10 days of release, some of the Bishop butterflies
were recaptured along the California coast just north of
Los Angeles and in the Santa Barbara area. Around half
a dozen total were sighted back at the Calif. coast. So this
group did not appear to have much difficult crossing
the 13,000-14,000 foot Sierra Nevada Mountains. None
apparently stayed in the Bishop area according to
a local naturalist (Derham Giuliani) who was monitoring
But no butterflies from the Saline Valley group were
recaptured back at the California coast or anywhere outside
the valley. When Derham checked the Saline
Valley monarch roosts in late November, lots of the
tagged monarchs were still there and they were still there
in mid December.
So it appears the reason the tagged monarchs released
in the Saline Valley stayed there is because the butterflies
detected proximate environmental cues that "overrode"
the southward migratory urge. In other words, the mountains
were no barrier to movement, the butterflies simply had
no "desire" to leave the place (balmy winter climate,
blooming Mule Fat bushes, and a permanent creek running
through this desert area).
> In other words, there does not appear to be any innate
> requirement that they _complete_ the migration to the Pacific
> coast. The migratory urge may be far less focused than many
> people have assumed. This raises an interesting possibility:
> that Monarchs from any part of the continent would, when
> introduced into another part of North America, would migrate
> along with the other individuals from that region.
Exactly. In fact back in the late 70's when I was an undergrad
at UC Davis, Prof. Art Shapiro urged me to get ahold of
some tropical monarchs from a lepidopterist he knew in Samoa
and raise them outdoors in late summer here in California to see
if they would become diapausers in September and have a
migratory urge to fly to the California coast. I never got around
to doing that most important experiment. Of course in today's
political climate an international transfer experiment could never
Paul Cherubini, Placerville, Calif.
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