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Thanks Phil.
Your link
http://www.migratorydragonflypartnership.org/index/welcome
advertizes an interesting project and requests collaborators, but I couldn't find much real info about migration there except at the last external link that they provide, to a journal review specifically on dragonfly migration by Michael L. May. This downloads a free PDF file that's detailed and well worth reading (published November 2012, so quite recent). Apart from the work on the Green Darner (A. junius), though, where the evidence from several directions seems quite persuasive, much of the rest of the info from other species on 'migration' is rather preliminary or circumstantial: the five species listed on the Xerces site and by May are fingered as migratory, with a few other suspects, so it seems to be a highly specialized habit -- they don't all do it. Confidence-lowering disclaimer comments recur in Xerces like 'migratory flights south in Fall, presumably their offspring, but poorly known' where 'presumably' presumably means that it makes sense to think that it's indeed the northern adult offspring that move south, but that this doesn't (presumably) exclude the possibility that some Anax or other adults may make 2-way round trips, S->N->S, that would qualify as real migration.
The general idea seems to be that where dragonfly 'migration' is suspected to occur, it is considered highly dispersive in both directions, S->N (early) and N->S (late) and is not highly site-specifically targetted like that of Canadian and E. USA monarchs that winter very locally in Mexico. This lessens the need for terminally accurate navigational compass mechanisms so far in dragonflies, one of the more interesting implications from insect and other migrations -- May (2012) doesn't mention it much, except to indicate that migrants may follow contours like shorelines.
A good read nonetheless.
Steve (Hfx)
________________________________________
From: naturens-owner@chebucto.ns.ca [naturens-owner@chebucto.ns.ca] on behalf of Phil Schappert [philjs@eastlink.ca]
Sent: Sunday, July 5, 2015 2:19 PM
To: naturens@chebucto.ns.ca
Subject: RE: [NatureNS] Queen Bee
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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