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At 3:58 PM +0000 7/5/15, Stephen Shaw wrote:
>The Xerces outfit (see url below from Peter) has quite a wide mandate.
The founder of the Xerces Society, Bob Pyle, was (and still is) a
hero of mine. His book, the Audubon Society Handbook for Butterfly
Watchers, was a godsend for me in the mid-80s and should be required
reading for any/all butterfly watchers...
>I'd heard about one species (Anax junius), but was surprised to
>learn from the Xerces site that they know or suspect that at least 5
>species of dragonfly are north-south migratory, like some
>populations of the monarch butterfly. Most of the monarch
>populations world-wide are non-migratory, and surprisingly,
>molecular phylogeny reveals that the migratory habit of the North
>American groups apparently developed as a later offshoot in
>evolution, not early.
I don't find it particularly surprising that many dragonflies are
migratory, only that it took us so long to figure it out (!). For
more info about dragonfly migration, I urge folks to visit the
Migratory Dragonfly Partnership site at
http://www.migratorydragonflypartnership.org/index/welcome
The migratory habit (I use "migration" loosely when in comes to
Monarchs since they are only one-way migrants) in North American
Monarchs is likely due to a single factor, the natural north
temperate (seasonal and continental) range of Asclepias syriaca, the
"common" milkweed. I think that Monarchs are best considered
"re-colonists" in their spring northward movements since they follow
the seasonal emergence of milkweed and "leap-frog" over preceding
generations.
The Danaids, as a whole, are almost entirely restricted to the
tropics except for two species, D. plexippus (the Monarch) and D.
gilippus (the Queen), however, the Queen is a far more recent
arrival, dependent on the rapid incorporation of A. curasavicca (the
tropical milkweed) into gardens across much of North America. The
Queen is now known to "migrate" as far north as New Jersey in some
years. There are many other migrants in the Danaidae, including the
Blue Crow (Euploea core), which congregate seasonally in roost sites
due to seasonal changes in moisture regimes (eg. dry and wet
seasons), all WITHIN the tropics.
Phil
--
Phil Schappert, PhD
27 Clovis Ave.
Halifax, NS, B3P 1J3
philschappert.ca
imaginaturestudio.ca
imaginaturestudio.blogspot.ca
philschappert.com
"Just let imagination lead, reality will follow through..."
(Michael Hedges)
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