Tuesday, February 18, 2014

Common Dragonflies of Anacortes: The Three Amigos!

Anacortes is a great place to dragonfly.  It's where the Happy-face Darner was discovered – at Cranberry Lake on October 22, 2006 – and where splash-dunking was first filmed.  In addition, the previously-unknown phenomenon of spin-drying was also discovered at Cranberry Lake.  All told, something like 25 species of dragonflies and damselflies have been seen in Anacortes.

If you see a red dragonfly in Anacortes, you know for sure that you've just seen a meadowhawk.  Similarly, a yellow dragonfly is a freshly-emerged – that is, a teneral – meadowhawk.  To summarize:

red dragonfly = meadowhawk
       yellow dragonfly = teneral meadowhawk

There are three meadowhawks that are most common in Anacortes – the three amigos.  They are, in order of flight date, the Cardinal Meadowhawk, the Striped Meadowhawk, and the Autumn Meadowhawk.  The meadowhawks and their flight seasons are shown below:

The above histograms show the flight season of each meadowhawk in terms of the percentage of observations.  For example, roughly 40% of all observations of Cardinal Meadowhawks occur in July, and about 20% occur in August.

From these histograms, you can conclude that if you happen to see a red dragonfly in May, it is a Cardinal Meadowhawk.  A red dragonfly in June is almost certainly a Cardinal Meadowhawk.  In July and August, a red dragonfly could be either a Cardinal Meadowhawk or a Striped Meadowhawk.  In October and November, red dragonflies are almost certainly Autumn Meadowhawks.  In general, the shift in flight season is quite apparent from the shift in the peaks of the histograms.

There is a similar shift in the range maps of these species as well.  This can be seen in the maps shown below:

Notice that the Cardinal Meadowhawks are primarily a western species.  The Striped Meadowhawk go roughly from the west coast to the Rockies.  On the other hand, the Autumn Meadowhawk is primarily as eastern species, with just a relatively small enclave on the west coast.

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