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

[Dennis Paulson]

I have been waiting to respond to this thread, hoping I would get a  
sunny day. The weather had been nice in the Seattle area until the  
last week in September, when it went completely to pot, with much  
lower temps and lots of rain. This is about a month earlier than such  
weather usually comes in, typically in late October, and it really  
seemed as if winter came a month early this year. We haven't had a  
really good day since then until today, although there have been  
brief sun breaks on and off. Today the clouds dissipated by early  
afternoon, and I made a beeline for the closest place to Seattle  
where I have found lots of odonates, about an hour from my house with  
the heavy Saturday afternoon traffic. I didn't really know what to  
expect, wondering if the long spate of adverse weather had wiped out  
dragonfly populations for the year.

Anyway, I didn't get to the lake until 15:00 hours, thanks to that  
traffic. The temperature was 63° F on the thermometer in my car,  
which is fairly accurate. These species were present and active:

Lestes congener - both sexes very common, but no pairs seen
L. disjunctus - few males
Aeshna canadensis - few males
A. palmata - males common, one ovipositing female
A. umbrosa - males common
Sympetrum vicinum - both sexes common, mating and ovipositing

These are all species normally present late in the season, several of  
them into November in some years. It appears that all of them  
survived the lengthy bad weather, and some may have been active  
during brief sunny spells. I doubt if any of them emerged since the  
weather turned bad around 24 September, so I think they were present  
as adults throughout that period. I caught quite a few of the  
darners, and none had especially worn wings, nor did the spreadwings  
and meadowhawks that I photographed, so I wonder if the fact that  
they were dormant for a considerable amount of time actually caused  
them to have less wing wear late in the season than I would have  
expected.

As it got later, a ridge to the west started obscuring the sun, and  
the sunlight left the lake by 16:00, as did all the odonates present.  
The Aeshna and Sympetrum disappeared, but the Lestes congener, which  
had been collecting in shrubs in the sun just to the east of the  
lake, began following the sun up into the trees. More and more of  
them flew up from the low shrubs and landed on leaves of large trees  
that were still in the sun. I was standing on a road right next to  
the lake, with the sky above me, so I could see this flight easily as  
one after another crossed the road. Some individuals flew sallies out  
from the leaves, presumably flycatching. The highest I saw one go was  
about 20 meters, which was about 2/3 of the way up to the treetops,  
but I wouldn't be surprised if they went higher. I had the feeling  
that a good proportion of the individuals present were moving up into  
the trees. By 16:20, the temperature had dropped to 57° F, and all of  
a sudden I could see no more movement among the Lestes. I assume they  
had gone to roost by then, and I can only assume that the roost sites  
of many individuals were well above the ground. Being that high, the  
sun would presumably hit them earlier in the morning than if they  
stayed down at the edge of the lake, and they were certainly able to  
remain active a bit longer by following the sun. Some individuals  
that I saw in the shrubbery had closed their wings, I should add, as  
they do when they go to roost.

This afternoon flight up into the trees is something that I haven't  
seen before, although I suspect it might be commonplace, and I just  
haven't been at the right place and time to see it. I suspect it has  
been written about for one species or another.
-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



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