Tuesday, September 30, 2014

Six Splash-Dunks and a Spin-Dry

Here's a recent video from Cranberry Lake in Anacortes.  It was taken on September 28, 2014, and shows a series of six splash-dunks, followed by a spin-dry that sheds a lot of water drops.

The dragonfly in this video is definitely a darner, though it could be either a Paddle-tailed Darner or a Shadow Darner – these are the two darners flying at the lake now.

We saw 15 splash-dunk events that day, in about an hour of observing, with the number of splash-dunks ranging from 1 to 8.  This is the peak season for splash-dunking, but soon the activity will start to taper off.  Here's a plot of the splash-dunk activity per month for the last three years.

We haven't seen any sticking events yet, where the dragonfly gets stuck in the water.  As the temperature drops below 65˚ F we expect to see these events start to occur.

Just to fill in the details on the splash-dunk/spin-dry suite of behaviors, we present some of the key features below.

First, the basic idea is of splash-dunking is illustrated schematically below:

Here we see a dragonfly plowing into the water a number of times (six for the above video), for the purposes of cleaning its body.  In a splash-dunk, the dragonfly completely immerses itself in the water, and comes to rest for about half a second.  This is in contrast to getting some water to drink, where the dragonfly just barely touches the water, and keeps flying at normal speed.

After a series of splash-dunks, the dragonfly gains some altitude and performs a spin-dry motion at 1,000 rpm to shed the water – which often comes off in a visible halo of water droplets.  So just what is a spin-dry?  Briefly, it's a tumbling, head-over-heels motion, like a somersault, or a diver spinning on the way to the water.

There is a lot of confusion on this point, so to be specific, let's look at a dragonfly and its three principle axes of rotation:

The spin-dry occurs about the dragonfly's "pitch" axis of rotation – that is, the axis that passes along the length of the wings.  This gives the head-over-heels motion mentioned above.  A sketch of a spinning dragonfly is shown next:

Finally, it was mentioned that the dragonfly does its spin-dry at 1,000 rpm.  That figure is obtained by counting the number of frames of high-speed video needed for a rotation, and converting the result to revolutions per minute (rpm).  Here's a plot of data from a number of spin-dry videos:

The red line shows the average spin rate, which is just above the 1,000 rpm mark.  This spin rate results in a centripetal acceleration of about 10g, which is more than enough to throw off any clinging water.

These are the key features of splash-dunking and spin-drying.  With a keen eye, these events can be seen in realtime at your local lake or pond.

Thursday, September 11, 2014

Anacortes Field Trip: Saturday, September 13

Greetings Dragonfly Enthusiasts!

I can hardly believe how favorable the forecast is for this Saturday, September 13.  The weather's great, the dragonflies are out, and all systems are go!

Here are some details:

Field Trip Plans

1).  Start around 11:00 am at Heart Lake in Anacortes.  Heart Lake is right next to the road that takes you up to the top of Mt. Erie.  Meet in the southeast corner of the parking lot, which is the area farthest from the boat launch.

2).  Go to Smiley's Bottom around noon for a lunch break and to use the facilities there.  We will carpool at that location and proceed to Cranberry Lake.

3).  Arrive at Cranberry Lake around 1:00 pm.  This is where we hope to see some splash-dunking and spin-drying.  We'll probably finish up and return to Smiley's Bottom around 2:00 or 2:30 pm, depending on the activity level.

Here's a map showing the relevant locations:

To help you prepare for the field trip, here are photos of the damselflies and dragonflies most likely to be seen Saturday:

Clockwise from upper left: Spotted Spreadwing, Tule Bluet, Northern/Boreal Bluet, Pacific Forktail.

Clockwise from upper left: Paddle-tailed Darner, Paddle-tailed Darner (Mr. Happy-face), Shadow Darner, Blue-eyed Darner.

Clockwise from upper left: Cardinal Meadowhawk, Autumn Meadowhawk, Four-spotted Skimmer, Eight-spotted Skimmer.

Clockwise from upper left: Blue Dasher (male), Blue Dasher (female), Western Pondhawk (female), Western Pondhawk (male).

We look forward to seeing you this Saturday!

Monday, September 8, 2014

The Whisperer Speaks Tomorrow!

Greetings Dragonfly Enthusiasts!

Just a reminder of the presentation "Adventures With Dragonflies" to be given tomorrow evening at the Skagit Audubon general meeting.  Details, including time and location, can be found at the following links:



We look forward to seeing you there!

Below you will find a "Dragonflies 101" handout for tomorrow's talk.  It includes some of the key concepts to be covered.  Feel free to print a copy and bring it with you to take additional notes.

Field Trip
Don't forget about the field trip we've been planning for Saturday, September 13.  The weather forecast looks favorable, and the dragonfly activity is quite high, so all indications are go.  Here are the basic plans for the field trip:

1).  Start around 11:00 am at Heart Lake in Anacortes.  Good dragonfly activity here, including lots of perching, so bring a spotting scope if you have one.  Binoculars and cameras are great, too.  For recent adventures at Heart Lake check the following links:



2).  Go to Smiley's Bottom around noon for a lunch break and to use the facilities there.  We will carpool at that location and proceed to Cranberry Lake.

3).  Arrive at Cranberry Lake around 1:00 pm.  The splash-dunk/spin-dry activity is quite high right now (this is the peak of the season), and we should have no problem seeing a number of events.  Also a good location to see perching Happy-face Dragonflies.  We'll probably finish up around 2:00 or 2:30 pm.

More details, including maps to the various locations, will be provided in a follow-up notice on Wednesday.  It should be fun to take some of information provided in the talk and apply it in the field!

Wednesday, September 3, 2014

The Whisperer Speaks Next Week!

Greetings Dragonfly Enthusiasts!

Betsy and I are looking forward to seeing you at the next meeting of Skagit Audubon, on Tuesday, September 9, where we will give a presentation entitled "Adventures With Dragonflies."  We also plan to lead a dragonfly field trip the following Saturday, September 13, weather permitting.

More information on the presentation is given below:

Stay tuned for additional information, including handouts and updated information about the planned field trip, and be sure to visit Skagit Audubon for more information about birding in Skagit County at http://www.skagitaudubon.org.

Feel free to bring your dragonfly photos, questions, or stories to share with the whisperer.

Monday, September 1, 2014

I Heart Heart Lake

We had a great time at Heart Lake a few days ago.  The lake gets its name from its very rough heart shape, as can be seen in the following map:

Heart Lake (center, bottom) in relation to downtown Anacortes.

In addition to the numerous Western Pondhawks that were there a couple days ago (see this post), we also observed a number of other dragonflies, including Blue Dashers and Eight-spotted Skimmers.

Perhaps most striking was the Cardinal Meadowhawk, with its intense red colors showing off nicely in the bright sun.  Here's an example of one of the males:

Male Cardinal Meadowhawk at Heart Lake.

In this next view you can see what I regard as its best field mark, the intense concentration of red color near the wing bases.

Male cardinal Meadowhawk.  Notice the dark red, opaque regions in the wings near the base.  An excellent field mark.

This field mark is completely diagnostic, and visible from almost any angle.  I'm always surprised field guides don't make a bigger deal of it.

Notice also the intense red color on the abdomen.  It almost over saturates the eyes.

The Cardinal Meadowhawks were also laying eggs, which they do while attached in tandem.  Here's an example:

Cardinal Meadowhawks laying eggs in tandem.  The female dips the tip of her abdomen in the water to deposit her eggs.

While this pair was laying eggs, a lone male was trying to break them apart so he could replace the current male, as can be seen below.  It didn't work, though he was pretty persistent.

A lone male Cardinal Meadowhawk unsuccessfully attempting to break apart an egg-laying pair.