[Odonata-l] Planiplax (and more) in Texas! RFI

[opihi@mindspring.com]

Howdy folks,

We have been having some big excitement this week at Bentsen-Rio Grande Valley State Park (in extreme southern Texas). A dragon, possibly more than one, which I initially mistook from photos as Erythemis peruviana, has turned out instead to be Planiplax, a genus never before recorded in the US! Photos by Jan and David Dauphin, who first discovered the critter, are on their website here: 

http://outdoors.webshots.com/album/540330134EjHYsB?start=72

This dragon was first spotted on Monday 6-2-08, and has been seen each day since. The Dauphins initially reported 2 and perhaps as many as 4; I have yet to see more than one, but the resaca where it has been lurking is swarming with Red-tailed Pennants (Brachymesia furcata), as well as a number of other brilliant red Libellulids, and while a Planiplax leaps out of the crowd when it passes nearby, it could be easily missed at a distance of more than a few meters.

The most likely species is P. sanguiniventris, according to Needham, Westfall, and May the only member of the genus recorded from the Mexican states nearest the US. However, we have been stymied in attempts to obtain a specimen to confirm this. I have spent over three hours at the boat ramp, the site of all observations so far, and seen the critter exactly twice. The Dauphins, who have been able to spend far more time searching than I, confirm that they see it roughly once per hour. These once-hourly sightings are uniformly very brief, never more than a few seconds, and only twice in the dozen or so encounters has it ever been seen to perch. Otherwise it remains stolidly offshore. Even getting photos has been impossible in all but one case, and none of us has even gotten close to swinging a net at the little bugger.

Which brings me to my first question: Does anyone out there have experience with this species in the field that might help us in trying to capture one, or at least explain why it is so elusive? Martin Reid, who saw it with us today, hypothesized that it might be patrolling the entire wetland, passing by once per hour because it takes it that long to circumnavigate the entire resaca (a.k.a. an oxbow lake, a long and winding body of water). Our other thought is that it might be hiding out somewhere, maybe in the shade, maybe too far offshore to be picked out of the masses of B. furcata, and not visiting the boat ramp often; or that it might actually be sensitive to human presence, refusing to perch or remain for long in the boat ramp vicinity because of the persistent human presence there. Any of these theories sound consistent with this genus' behavior where it is more common further south?

More to the story: the Planiplax is far from alone. In addition to this first-for-the-US occurrence, we have seen, over the past few days, a first Texas record Metallic Pennant (Idiataphe cubensis), a first LRGV record Antillean Saddlebags (Tramea insularis), first park records of Black Pondhawk (Erythemis attala) and Three-striped Dasher (Micrathyria didyma), and rare but not unprecedented species that, in any other week, might have been the highlight odonate, such as Tawny Pennant (Brachymesia herbida), Pin-tailed Pondhawk (E. plebeja), Checkered Setwing (Dythemis fugax), Narrow-striped Forceptail (Aphylla protracta), and Halloween Pennant (Celithemis eponina - an abundant species further north but decidedly rare in the LRGV).

This astounding collection of species seems far beyond what could happen by mere coincidence, and I have spent too much time watching odonates at this particular boat ramp over the past two-and-a-half years to attribute this to increased observer attention. I have heard butterfly-watchers relate occurrences of rare Mexican butterflies to strong southwesterly winds following autumn cold fronts. We have had very strong southeasterly winds over the past few days, and several of the species involved seem to have Caribbean affiliations (I. cubensis and T. insularis especially). Does this seem like a sound explanation for this occurrence, or does anyone have an alternative explanation for why so many rarities might appear at the same time?

Thanks in advance for any insights that anyone can provide. And thanks also for reading this far, this e-mail really turned into something of an epic...

Cheers,

Josh


Joshua S. Rose, Ph.D.
Natural Resource Specialist
World Birding Center
Bentsen-Rio Grande Valley State Park 
http://www.worldbirdingcenter.org/sites/mission/index.phtml 
joshua.rose at tpwd.state.tx.us 
956-584-9156 x 236