Around August and September there’s an intermittent phenomenon at coastal areas of the Pacific Northwest that involves the directional movement of dragonflies (typically southward) and there’s a lot to learn about what exactly is going on. This has been observed most frequently at southern Washington and northern Oregon coastal areas, with sporadic reports from further south into California. This phenomenon is commonly referred to as a migration, but whether it is truly a directed migration (like in the sense that many birds migrate south each year) or something else is one of those things that isn’t yet clear.
|A nearly mature male Variegated Meadowhawk (Sympetrum|
corruptum). Note the overall reddish-brown color, the pair of
yellow spots on the lower side of the thorax, and the orange
veins along the leading edge of the wings.
Some years there are lots of reports of moving meadowhawks on the beaches, and some years there are hardly any. Last year—2010, was a big year for them. So much so, that people who otherwise give no thought to dragonflies at all took notice of the huge numbers, even using terms like “apocalyptic” and “plague”. The events even made headlines at local news outlets such as the Cannon Beach Gazette in Oregon. You can still see their article here.
I think it’s likely that these coastal concentrations are the result of regional topography: East winds are funneled down the Columbia River to its mouth and lots of meadowhawks go with it; when they reach the ocean they resume their southerly course. There have been some reports of meadowhawks flying onto beaches from the ocean (from the west). This suggests that some of them get blown out to the open Pacific, then have to make it back to land (or else become fish food following exhaustion). Looking at this at the bigger scale, our coastal flights may only be a small observable slice of a much more widespread migration that is otherwise invisible because the meadowhawks are so spread out.
Record Your Observations
|Immature female Variegated Meadowhawk (Sympetrum|
corruptum). The overall color is more yellow with
more obvious white spots on the abdomen and white
stripes on the thorax.
These movements, when they occur, vary widely from pretty light (a few passing a fixed point per minute) to major (in the hundreds per minute) to exceptional (in the thousands per minute). When you’re observing a directional movement of dragonflies the best way to gauge their numbers is to look across a wide open area (like a beach, or an open dune area, or a parking lot) perpendicular to the direction of flight and count the number of individuals that pass your line of sight over a period of time—say five minutes. Divide the total count by the number of minutes to get the rate. It can be helpful to pick a landmark at the other end of your line of sight—a utility pole, a rock, a car, etc., and imagine a “finish line” between you and the landmark.
Additional information that is helpful include the date, location, the times that the flights start and stop (or at least the beginning and ending times of your observations), the direction of movement (determined with a compass, if possible), and general weather conditions—particularly wind direction. If you conduct formal counts like described above, include the length of your line of sight. Of course the species involved is important and if you are unsure of what you’re looking at, photos and video (even of distant subjects) are often helpful for identification later on. As I said earlier, the Variegated Meadowhawk is the primary species seen in directional movements at coastal Northwest locations and I have some photos of that species here and you can view a lot more at BugGuide.net.
Mature male Variegated Meadowhawks are largely red and brown on the body and the variegated patterning gives them a dusty orange appearance from a distance. Mature females tend to be more brown instead of red. Their wings are clear, but the major veins along the leading edge of each wing are orange which can be noticeable at close range. Immature, or more recently emerged, individuals are overall yellow or yellowish-orange with white spots on the abdomen and white stripes on the thorax—each white stripe on the side of the thorax terminates at a yellow spot. The veins along the leading edges of the wings are yellow instead of orange. As they mature, the white stripes and spots darken, but that pair of yellow spots on the side of the thorax persist.
|A fully mature male Variegated Meadowhawk (Sympetrum corruptum) without any white spots or stripes.|
|This male Variegated Meadowhawk (Sympetrum corruptum) is intermediate in maturity still with white spots and stripes, but those are fading.|
If you see a lot of Variegated Meadowhawks not flying, but just hanging around open coastal areas away from fresh water like parking lots, parks, and beach areas with drift wood, that’s worth noting too. It may be that a flight just ended and they are taking a break to rest and feed. Maybe the conditions that were good for a flight ended and they are waiting for the right time to start again. Again, recording the weather conditions during your observation may be very helpful.
Report Your Observations
So now that you have some information to share, what do you do with it? At the very least, report your information to an appropriate listserve so that it’s there for others to glean and perhaps combine with other reports. This also alerts readers when a flight may be going on in their area so they can make their own observations. For the northwestern US and western Canada report to the NW_Odonata Yahoo Group; in California it’s the CalOdes Yahoo Group. If you’re not a member of any of these listserves, find someone who is and have them post your information. You can let me know and I’ll make sure that your information ends up in the right place.
Some people collect observations in their local areas such as Mike Patterson (North Coast Diaries) in the Columbia estuary area of Oregon and Washington, and Range Bayer and Terry Morse in Lincoln County, Oregon. At the continental scale, Chris at The Dragonfly Woman is collecting reports of dragonfly swarms (both migratory and feeding swarms) from throughout North America. She has a handy web form where you can report your observations and help out with her research.
Research is also going on at the molecular level to figure out from which latitude, roughly, migrating Variegated Meadowhawks originate. There is a known correlation between the abundance of deuterium (a hydrogen isotope) in the tissues of dragonflies and the latitude where they lived as a nymph and emerged. This analysis, which uses one wing from each specimen, will give us some indication of how far these meadowhawks had traveled at the time they were collected. Dennis Paulson is accepting specimens of Variegated Meadowhawk for this research and he is interested in both recently emerged individuals from local populations and individuals which were part of a directional movement. Either dried or acetoned specimens can be used. He follows the listserves mentioned above so you can contact him that way, or just let me know and I’ll put you in touch.
So get out there and look for migrating meadowhawks. Anyone can make a contribution!
Postscript, 18 August 2011
Dennis Paulson reminded me that major Variegated Meadowhawk flights were also observed at San Juan Island, Washington and in the mountains of western Montana during 2010, so this phenomenon is not restricted to the outer coast. Naturally we’d like to hear about these flights wherever they are observed.
Dennis also elaborated on a Migratory Dragonfly Partnership, including representatives from Canada, the US, and Mexico that will be putting together materials and protocols to involve the public in recording and monitoring dragonfly migration across the continent. The deuterium analysis that I mentioned above is part of this project which is funded by the US Forest Service, through The Xerces Society for Invertebrate Conservation (based in Portland, Oregon). I’m sure we’ll be hearing more about that over the next year.