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.
Acknowledgements
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.
