Wednesday, November 25, 2015

Splash-Dunk Derby

An article submitted to Argia.

A Splash-Dunk Derby at Beaver Pond

James S. Walker
Anacortes, Washington

One of my favorite places to dragonfly is the aptly named Beaver Pond in Winthrop, WA.  Located just down the hill from the spectacular Sun Mountain Lodge, it contains a wealth of wildlife, including beavers, an Osprey nest, lots of warblers, rafts of waterfowl, stands of Ponderosa Pines and – of course – flights of dragonflies.

My wife Betsy and I visited Beaver Pond early in August 2015 and enjoyed a surprisingly active day of dragonfly behavior.  There weren’t many species present that day – one darner, one meadowhawk, and three damselflies – but the intensity of the splash-dunk behavior was amazing.  This article reports on our observations.

Observing from the Footbridge

When you walk to Beaver Pond from the parking lot, the first thing you encounter is a sturdy wooden footbridge across the end of the pond.  Figure 1 shows the footbridge, and part of Beaver Pond in the background.  The bridge is a perfect viewing platform for dragonfly behavior, and the observations reported here were all obtained at that location.

Figure 1 Beaver Pond and the footbridge that served as a viewing platform for a series of splash-dunks.

There were generally about 10 or 12 Paddle-tailed Darners (Aeshna palmata) flying low over the water in this area at any given time.  They hover frequently, as in Figure 2, but they also swoop low over the water to catch small flies and chase rivals.  Some disappear into the bushes to perch, while others return to the pond refreshed, resulting in an active, constantly changing population. 

Figure 2 A male Paddle-tailed Darner (A. palmata) hovers as it protects its territory.

As soon as we arrived at the bridge, we began to see splash-dunk events involving the darners.  When we see this kind of activity, we always call out loud, “One, two, three …” as the splash-dunks progress, and then we look for – and generally see – the spin-dry (Walker, 2011a) at the end of the event.  Observing from the bridge is particularly beneficial for this kind of observation, because it puts the observer at eye level with the spin-dry.  We generally had great views of the dragonfly curled up and spinning, and we could usually see the droplets of water spraying off in all directions.

After the spin-dry, we record the number of splash-dunks of that event, which ranged from 1 to 6 on this day.  In most cases we’ve observed over the years, there wouldn’t be another splash-dunk event for several minutes.  In fact, at Cranberry Lake in Anacortes, a good day of splash-dunking results in one event every ten minutes, and a really good day has one event every five minutes.  On this day at Beaver Pond, a new event started up as soon as we had written down the results of the previous event.  It was almost nonstop splash-dunking for a while.  At the peak of the activity, there was roughly one splash-dunk event every 12 - 15 seconds, and a couple times there were two splash-dunk events going on simultaneously – something we hadn’t experienced before.

One of the other things we noticed about the splash-dunk events at Beaver Pond is that they generally involved a larger number of splash-dunks than is usual.  Typically, we see more 1 splash-dunk events than any others, but here most of the events had 3 or 4 splash-dunks.  A plot of the results of the splash-dunking for period of about 10 minutes is shown in Figure 3.  Notice the peak corresponding to 3 and 4 splash-dunks.

Figure 3 Number of events observed at Beaver Pond with splash-dunks ranging from 1 to 6.

This distribution is quite different from that seen over the years at Cranberry Lake (Walker 2011b, 2014), where we’ve observed roughly 500 events.  These observations have produced a distribution of splash-dunk numbers that has its largest value at one splash-dunk, and decreases by roughly one half with each additional splash-dunk.  Further observation will reveal if the distribution seen at Beaver Pond is simply a fluctuation due to the small number (20) of events observed (quite likely), or an indication of distinctly different behavior at that location.

Interactions during Splash-Dunking

Another interesting aspect of the splash-dunk derby at Beaver Pond is that lots of interactions were observed between splash-dunking dragonflies and others in the vicinity.  Usually, splash-dunks are so separated in time and space that no interactions take place.  In this case, however, all the events occurred in a confined area, and in rapid succession.  Thus, it was common for a dragonfly to splash-dunk once or twice, and then to be intercepted by another dragonfly that would grab hold of it as it tried to fly up from the water.  They would struggle briefly before separating.  It may be that the intercepting dragonflies (males) were checking the splash-dunking dragonflies to see if they might be females.  It seemed like many of the splash-dunk events would have continued to more splash-dunks if they hadn’t been interrupted.

In addition, we saw several females engage in splash-dunking, which is unusual – most splash-dunks are performed by males, because they spend the majority of their time patrolling over open water.  When a female would start a series of splash-dunks at Beaver Pond, a male would quickly intercept her and attach in tandem.  To see this behavior happen several times in just a few minutes was unprecedented.

Unusual Conditions at Beaver Pond

It’s natural to ask why the splash-dunk activity was so intense on this particular day.  There’s no way to know for sure – it may be simply a convergence of circumstances that combine many of the necessary conditions for splash-dunk behavior.

For example, we have good evidence that splash-dunking serves to clean the body (Walker, 2013).  In one notable case, we watched as a darner with a spider web trailing from its abdomen initiated a series of splash-dunks.  After the first two splash-dunks the web was still attached, but after the third splash-dunk the web was no longer visible.  The darner then gained altitude and did a spin-dry.  Thus, conditions that might give a dragonfly the urge to clean itself may produce more splash-dunking, as may a mass emergence of a species that is particularly prone to splash-dunking.

On this day there was one unusual condition that deserves mention, and was apparent to us the minute we stepped out of the car.  Our visit occurred when forest fires were raging nearby, and forced evacuations of Sun Mountain Lodge a few days after our visit.  As we exited the car we noticed a strong odor of smoke, and saw a distinct haze in the air.  One can only speculate whether the suspended particulates in the smoke might have induced a desire to splash-dunk to clean the body and clear the spicules.  At the moment, it’s just an isolated observation, and there may be nothing to it, but it’s something to consider.


I would like to thank Betsy Walker for help with these observations.

Literature Cited

Walker, J. S. 2011a.  Spin-Dry Dragonflies.  Argia 23(3): 29-31.

Walker, J. S. 2011b.  Splash-Dunk Analysis, 2011.  Argia 23(4): 29-30.

Walker, J. S. 2013.  The Strange Case of the Constipated Darner.  Argia 25(3): 29-30.

Walker, J. S. 2014.  Splash-Dunk Analysis for 2011-2014.  Argia 26(4): 32-33.

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