[Odonata-l] effect of rain on ode numbers?

[Bob Glotzhober]

I have seen Cordulegaster erronea (Tiger Spiketail) flying in light rain
also. Since they live in heavily shaded under story conditions, the
light rain and the darkness that accompanies it is not much different
from the low-light conditions they typically fly in. As long as it is
warm enough, and not a downpour, it probably does not make much
difference. Most pond species disappear into the vegetation as soon as
it gets cloudy. 

 

A couple of us here in central Ohio have noted that for river species,
heavy rain is typically accompanied by quickly raising water levels. We
have hypothesized that not only might the heavy rain physically knock
adults down, making them easy prey, but the rising water levels may wash
away larvae that have moved to the stream edge and are about to emerge,
causing a one week or longer drop in population levels. Larvae that are
on the bottom and away from the stream edge are protected by rapidly
reduced current speed near the bottom - but those that are about to
crawl up, or are crawling up, are not so protected. Sorry - no data to
support this - just anecdotal observations.

 

Bob

 

====================

Robert C. Glotzhober             614/ 297-2633

Senior Curator, Natural History         bglotzhober at ohiohistory.org

Ohio Historical Society         Fax: 614/ 297-2546

1982 Velma Avenue

Columbus, Ohio  43211-2497

 

Visit the website of the Ohio Historical Society at:

  www.ohiohistory.org and check out our online collections catalog.

See or purchase Dragonflies and Damselflies of Ohio or the Cedar Bog
Symposium II at OHS's new E-Store:  http://www.ohiohistorystore.com/ 

Visit the Ohio Odonata website at:
http://www.marietta.edu/~odonata/index.html

 

 

________________________________

From: odonata-l-bounces at listhost.ups.edu
[mailto:odonata-l-bounces at listhost.ups.edu] On Behalf Of Sulka Haro
Sent: Tuesday, October 09, 2007 2:13 PM
To: Chris Hill
Cc: odonata-l
Subject: Re: [Odonata-l] effect of rain on ode numbers?

 

 

Hi!

 

We had a discussion about that back here in Finland after members of the
Finnish Dragonfly Society observed a drop in the numbers after rainy
periods and the general consensus was that if most of the specimens
don't get to feed for an extended period of time due to weather
conditions, the numbers will drop as the dragons simply die off. Does
someone on the list have actual research data on the survival of dragons
when deprived of food? 

 

I do recall seeing Aeshna grandis fly in light rain but most species
seem to avoid hunting in rainy conditions.

 

This year demonstrated the effect here pretty well - the early season
was fantastic and a massive number of the early records were broken.
However in "early mid-season" the weather worsened dramatically for a
period of time, which caused a significant drop in the number of dragons
observed. Some fairly common species suddenly weren't that common at
all. 

Sulka

 

On 10/9/07, Chris Hill <chill at coastal.edu> wrote:

Hi,

Here in my corner of South Carolina, it's rained almost five inches
in the last week, with hard rains on about four days in a row.  It
turned sunny again yesterday.

How does rainfall like that affect dragonfly numbers?  Does that 
usually knock them down for a while?  I'm asking because I have some
students doing a research project on a common species, which is
suddenly less common!  I'd like to be able to guess whether the
dropoff is weather related and the odes will bounce back, or if it's 
more likely seasonal and they won't be coming back.

CH

************************************************************************
Christopher E. Hill
Biology Department
Coastal Carolina University 
Conway, SC 29528-1954
chill AT coastal.edu
http://ww2.coastal.edu/chill/chill.htm

"Research is just formalized curiosity." -- Zora Neale Hurston 


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