Monday, March 5, 2012

Migrant Meadowhawk Research Takes Wing


 
Last fall I wrote in It’s Time to Watch for Migrant Meadowhawks about migratory Variegated Meadowhawks (Sympetrum corruptum) which are sometimes observed in the Pacific Northwest flying south in large numbers. Those fall flights are most often observed on the coast—presumably because they are concentrated there during periods of persistent east winds, but large numbers have been observed elsewhere too.

Mike Patterson provides a taste of what a major flight looks like in a 2010 North Coast Diaries post, describing the undescribable, and below is one of his photos from that spectacular day.

A stream of migrating Variegated Meadowhawks (Sympetrum corruptum) on the northern Oregon coast, 2 September 2010. Photo by Mike Patterson. Click the image to view Mike's post about that day.
 
It seems likely that fall migrants reproduce when they reach destinations somewhere to the south, and their offspring return north the following spring to make the next batch of fall migrants. It may be (and probably is) more complicated than this, with reproduction occurring along the entire migratory path. Perhaps even some of those southbound fall migrants are able to survive the winter somewhere and start flying back north in the spring (even if they only get part way).

Northerly spring movements of Variegated Meadowhawks seem to be far more covert than fall movements. Perhaps the reason for this is that spring migrants are more spread out spatially and/or temporally; maybe predominant weather conditions during this time of year don’t have a concentrating effect (at least where concentrations are likely to be observed). There may be a combination of factors.

It’s difficult to be certain about much of this because there isn’t a lot of hard evidence. We have many scattered observations—of presumed migrants, of individuals in the southern US during the winter, of mature adults appearing in the north before emergence occurs, but nothing that solidly ties it all together in to a complete picture. That may change very soon...  ...and you can help.


Migratory Dragonfly Partnership and Stable Isotope Analysis 

In 2011, dragonfly experts, nongovernmental programs, academic institutions, and federal agencies from the United States, Mexico, and Canada collaborated to form the Migratory Dragonfly Partnership. This Partnership will combine research, citizen science, education and outreach to better understand North America’s migrating dragonflies, and to promote conservation of the wetland habitat on which they depend.

Some of the research orchestrated by the MDP involves stable isotope analysis. The concentration of deuterium—a hydrogen isotope—in the tissues of adult dragonflies can be compared with a deuterium gradient map to determine approximately where they lived as nymphs. With each tissue sample (a dragonfly wing) they’ll be able to say that the dragonfly emerged some approximate distance north or south of the location where it was collected. Perform this analysis on many samples from across the species’ range and from different times of the year, and a picture of their movements starts to come into focus.

Dennis Paulson is collecting wings of Variegated Meadowhawk for this stable isotope analysis. If you collect them (or already have specimens), particularly those that may be migrants, snip off one of the hind wings and send it to Dennis along with the specimen data (at least date and location; GPS coordinates are very helpful). Wings of recently emerged individuals from local populations, as well as those found in southern regions during the winter months will be valuable too. There’s no need to put the wings in alcohol—just send them dry which really simplifies shipping. Dennis follows many of the dragonfly listserves including NW_Odonata, CalOdes, SoWestOdes, and Odonata-L, so you can contact him through one of those venues, or you can contact me and I’ll put you in touch with him.


More Resources

The Migratory Dragonfly Partnership has a website up and running, although there is not much to look at right now. I’m sure they’ll have more content in the near future, including how you can contribute reports of migratory dragonfly flights. Keep an eye on this site.

Stable isotope analysis has been used to study another migratory dragonfly—the Common Green Darner (Anax junius), and you can read some of those results here.

I found this PDF on the use of stable isotope analysis as it relates to birds, but using it for dragonflies is the same idea. There are deuterium gradient maps of North America and Europe on page 239 which you might find interesting even if you don’t want to read the whole thing.

If you’re not familiar with techniques for collecting and preserving odonates, here are some helpful pages at the University of Puget Sound and OdonataCentral.org.


3 comments:

  1. I'd love to see a dragonfly migration. It was Chris of The Dragonfly Woman blog fame from whom I first heard of such a thing. The isotope research is fascinating. So, when is it considered winter with regard to dragonflies? How far south are they supposed to fly? Here in CA, I have photo records that recall a number of variegated meadowhawks mating September 17, 2011 at Wilder Ranch State Park in Santa Cruz Co. and several perching/patrolling October 13, 2011 on Black Hill in Morro Bay State Park in San Luis Obispo Co. when it was an unseasonably warm 90+°F. It never occurred to me that they may have flown in from elsewhere. I generally don't collect insects anymore. Plus both sightings were on State Park lands where collecting is prohibited.

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    1. Hi Katie. I've only been lucky enough to witness a good flight on the coast once. It is really cool.

      Those meadowhawks you saw in September and October certainly could have emerged somewhere far to the north. The species seems to pretty regular as far south as the Mexican Plateau with some records from Belize and Honduras (maybe vagrant that far south).

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  2. I was traveling in Belize this past December and as I walked along a beach one afternoon, thousands upon thousands of dragonflies were streaming in from the sea. It didn't seem to have an end. An absolutely mindblowing experience - I'd never witnessed that before. I've since inquired with others about this - not too many have been present for such events. It was very special indeed!

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