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

Dave McShaffrey mcshaffd@marietta.edu
Tue, 18 Jan 2000 09:00:30 -0500

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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