floating on water surface (was Wing Position) [ODO]

Nick Donnelly tdonnel@binghamton.edu
Tue, 18 Jan 2000 10:23:06 -0500

Odonata - http://www.listbot.com/cgi-bin/subscriber

The problem with fighting a reflection is that the beasts fell on their
back, which seems an ungainly way to attack a reflection.

t 09:00 AM 01/18/2000 -0500, you wrote:
>Odonata - http://www.listbot.com/cgi-bin/subscriber
>I agree with Nick's assessment that the idea of gauging stream velocity by
>floating is intriguing but problematic.  Let me toss out two other
>1.  The males are trying to demonstrate the relative density of fish in the
>stream.  Males that defend territories with a high density of fish may have
>all of their offspring eaten by those fish; thus that territory is not
>suitable for oviposition.  While getting eaten is probably not adaptive (for
>the male), if males are abundant then a few males getting eaten at
>territories full of fish probably won't hurt the population in the long run.
>Further, if the male is attacked immediately - but escapes - that may be a
>sign for him to move on to a site that would be more hospitable for his
>offspring (or his mate while she is ovipositing).
>2.  Perhaps the male is attacking a reflection - either his own in a
>territorial dispute, or the reflection of a prey item hovering over the
>Well, this type of speculating is fun, but it means we all have some
>observing and experimenting to do this summer, unless our colleagues down
>south steal a march on us.
>Dave McShaffrey
>Biology Department
>Marietta College
>Marietta, OH  45750
>(740) 376-4743 (voice)
>(740) 376-4753 (fax)
>----- Original Message -----
>From: "Nick Donnelly" <tdonnel@binghamton.edu>
>To: <dragonflies@listbot.com>
>Sent: Monday, January 17, 2000 8:15 PM
>Subject: Re: floating on water surface (was Wing Position)
>> Odonata - http://www.listbot.com/cgi-bin/subscriber
>> The idea that damselflies might gauge the velocity of water by floating is
>> intriguing.  One problem is that velocity varies tremendously from the
>> center of the river (or the thalweg, if the stream course is not straight)
>> and the bank, where it can be nearly zero even in a swift stream.  It is
>> little use to a female damselfly to "see" the current out in the stream,
>> unless she intends to lay her eggs there.  In the Tennessee case with
>> angustipennis I reported on, the male fell in the water well away from the
>> bank( and away from any vegetation for ovipositing), and in a complex bit
>> of the stream where the surface velocity must have varied widely within a
>> short distance.  In this instance, I doubt that the female could have
>> learned anything seful about velocities form watching the male on the
>> surface.
>> Also, because of lack of wetting, a male on the surface is also very much
>> subject to wind currents.  I doubt that they wind-surf for fun, but their
>> velocity is also subject to wind forces.
>> I have only seen this behavior once, but it seemed to be a display.  I am
>> aware that birders are debating "hazard" behavior, and I wish them good
>> luck in their quest.  Whether the Calopteryx are putyting themselvres in
>> harm's way or not, I believe they were displaying.
>> >Odonata - http://www.listbot.com/cgi-bin/subscriber
>> >
>> >In response to Paul's description of the male Calopteryx aequabilis on
>> >water, it sounds *exactly* like what the male C. haemorrhoidalis was
>> >in Ruppell's movie as described by Jill, which Ruppell thought was to
>> >illustrate the current speed (it was very effective!).  I have a tape of
>> >this movie and just looked at it the other night.  The points of contact
>> >the water were the hindwing tips and the abdomen tip, and the male did it
>> >several times, near the female.  With the sharp eyes of Odonata, I guess
>> >interested female could see this from 3 meters away, but Ruppell's
>> >male was much closer to its female.  On the only stream in my area where
>> >Calopteryx aequabilis is common, I've seen males displaying to females
>> >the hindwings almost stationary, as Ruppell also showed in his movie, but
>> >haven't seen the floating display yet.  I think I'll spend a day with
>> >beautiful damselflies this summer.
>> >
>> >I'm much more comfortable with the idea of this as a current-speed
>> >indicator than as a "foolhardy" or "posturing" male showing its bravery
>> >a stream full of rapacious fish.  The latter would make sense only under
>> >the Handicap Principle, in which females choose males with handicaps
>> >(stupidity?) because they have survived with them (so they must have a
>> >superior genome).  The huge masses of feathers used for display in some
>> >birds are often listed as evidence of this phenomenon, but there is still
>> >debate about its validity.  Drugging, drinking, and dangerous driving by
>> >young human males are also considered evidence of this principle, by the
>> >way.
>> >
>> >Above all, female odonates want good oviposition sites, and I suspect
>> >current speed is an important indicator for larval success in Calopteryx.
>> >I think the Male Calopteryx Float is right up there among the Wonders of
>> >Nature!
>> >
>> >Dennis Paulson, Director                           phone 253-756-3798
>> >Slater Museum of Natural History                 fax 253-756-3352
>> >University of Puget Sound                       e-mail dpaulson@ups.edu
>> >Tacoma, WA 98416
>> >http://www.ups.edu/biology/museum/museum.html
>> >
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*     Nick Donnelly      *
*     Binghamton, NY     *
* tdonnel@binghamton.edu *

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