Phoebis sennae migration (longish)

[Rob (Robert) Hilton]

Hello, 

Bob Augustine sent this to me to post to this list.  I have broken it up
into two segments.  He and I are interested in replies--I'm interested in
this phenomenon too but haven't researched it.  

Thanks, 

Rob Hilton
robert at csa.com
Bethesda, MD

+++++++++++++++++++++++++++++++++++
The Mystery of the Cloudless Giant Sulphurs (Phoebis sennae)

Has anyone reported Cloudless Giant Sulphurs heading north? I have
contended for years that their movement is southbound only, contrary to
most books, and I have yet to meet anyone who has actually seen one
definitely going north.

Even if one Phoebis sennae was seen in Washington heading north, it may
have been doing so merely to follow a bend in the river or an attractive
scent and may not have continued in that direction once it was beyond the
observer's view. Moreover, to create the sort of southbound flows that have
been seen many, many, sulphurs_not one or two_would have to have moved
north. There is no evidence whatsoever of any such movement ever taking
place around here (Washington). Most authors of lepidoptera literature
covering the middle Atlantic states omit the species altogether.

The reports from Folly Island, SC (near Charleston) from 1978-1980 (Aug.
24-Oct. 9) of as many as 125-323/5 minutes going NE are intriguing. At that
location, NE is exactly the direction of the coastline as far as Cape
Hatteras, NC. One wonders what happened when they got that far. If it
weren't for the reports from Florida, I'd be tempted to say perhaps they
flew on out to sea NE from Hatteras. Where _did_ they go? That's the kind
of flight we should have witnessed every summer that was followed by a big
southbound flight. (Could such a movement at such dates be responsible for
new broods heading south so soon afterward?) Where did the Florida
butterflies go?

I recall seeing similar numbers of these "flying Post-it Notes" streaming
off from Point Lookout, MD toward Cape Charles on peninsular Virginia (I've
no doubt some stopped in at Smith Island, but I'll bet they moved on from
there, as in Florida, heading SSE) on 10 Oct. 1987 across many more miles
of open water than the easier trip to the more southerly, nearby west shore
of the Chesapeake Bay in Virginia. Until that point, I had believed the
species--or at least its movements--were all coastal. But Point Lookout is
many (about 50) miles inland, and there were more there than at coastal
locations of similar latitude such as Chincoteague and Ocean City. Clearly,
they were coming from somewhere inland.

I saw a similar flight at Point Lookout in 1998 and traced it all the way
back to Route 50, the main E-W route between Washington and
Annapolis--mostly following the Patuxent River. Some were seen even further
north. That year eggs and caterpillars of Phoebis sennae were found at Cape
May and elsewhere. 

Where do all these butterflies go? Not so many years ago we were asking
that about Monarchs, and the question turned out to have a surprising answer.

The little research I've done on this intrigues me further. Did you know
that a number of related species also have northward movements like those
alleged to occur with Phoebis sennae? The final paragraphs in the species
accounts of the (1981) Audubon Society Field Guide to North American
Butterflies make for some fascinating reading (emphasis added):

"Like the White Angled Sulphur [Anteos clorinde], this high-flying species
[Yellow Angled Sulphur--Anteos maerula] engages in northern emigrations
that occasionally send some into the United States."

"Statira [Aphrissa statira], along with some species of Phoebis, takes part
in immense flights _out to sea_ from South America. Unlike the Cloudless
Giant Sulphur, Statira exhibits no such mass movements in North America,
and in fact is considered rather an uncommon resident species."


--Bob Augustine raugustine at tms-hq.com