Last week I talked a bit about how weather affects odonate behavior, my favorite topic in biology. Today I’ll go over the study I did to look at these weather related behaviors more closely. Like the little study I did that focused on damselflies and weather in my first college ecology class, this study was done at the wetlands in Fountain Creek Regional Park outside Colorado Springs, CO. This research was actually part of my undergrad senior thesis!
I had to work the summer I collected my data, but I went to the wetland most days after work and recorded observations from 4-5PM. I plopped down on the dock with all of my weather measuring equipment and watched the damselflies in a 5.5 square meter area along the edge of the pond for an hour. I divided the hour into 5-minute periods and recorded weather data (wind speed and direction, temperature, light intensity, barometric pressure, relative humidity, and whether it was raining or not) for the first minute of each period. I then spent the remaining 4 minutes counting the number of damselflies that flew within my study area. Part of that area was filled with cattails and the rest was over open water as you can see in the photo.
Having spent 14 years of my life in Colorado Springs, I can tell you one thing with certainty: in the summer it rains nearly every day between 4 and 5PM. This meant that I was out watching damselflies during the exact time the storms were blasting over Pike’s Peak and ripping across the plains. I would sit there watching these phenomenal storm clouds rolling straight toward me with fantastic speed. Guess who got rained on A LOT that summer? Me! I also got hailed on, was sandblasted in high winds, and was once driven running the half mile back to my car when the lightning got a little too close. However, the clouds moved so quickly (they have to build up a ton of momentum to make it over Pike’s Peak’s 14,115 feet!), the storms didn’t last long, usually 30 minutes at most. During that time, the weather would transform from hot, sunny, and still to cold, windy, and rainy in the span of a few minutes. It would usually rain, sometimes very hard, for 10 minutes or so. Then the storm would suddenly be over and it would become sunny, warm, and still again. This whole series of events would take place during my hour at the pond.
Now most sane people go inside during storms. Rain in Colorado is incredibly cold and the storms can be quite powerful with a lot of lightning. Call me crazy, but I loved curling my whole body into my enormous rain jacket and getting rained on. I was rewarded for my insanity too because I got to see some things that very few odonate people get to see.
First, I learned that there was a rather distinct pattern of behaviors that was associated with the weather patterns I observed. The damselflies were most active in sunny, warm, still conditions, the typical weather central Colorado experiences during the summer. They flew readily into and out of my study area, hunting, looking for mates, mating, and laying eggs. As soon as a storm approached, you’d see some pretty interesting things. As the clouds moved in and it became darker and cooler, the number of flights the damselflies made decreased so that fewer individuals flew during a counting period. As the wind picked up, the activity decreased even further. Flight activity ceased altogether if it started to rain. Of all the many hours I spent at the pond, I saw only a single damselfly flying while it was raining, and it was during a very light rain when the sun was still shining. Most interestingly to me, the damselflies would start to leave the pond when the weather deteriorated sufficiently. They were displaying pond abandonment behavior. However, as soon as the storm was over and the sun came back out, the damselflies would return to the pond and resume their normal activity as if nothing had happened at all. It was fascinating and I am so happy I got to see this behavior!
The flight activity of the damselflies at Fountain Creek Regional Park was clearly affected by the weather, but I was interested in knowing which of the seven weather parameters I measured were contributing to the flight activity I observed. I used a statistical procedure (multiple regression for those interested) to determine that light intensity, temperature, wind speed (but not direction), and whether it was raining or not were the weather parameters most closely associated with the flight activity that I recorded. Of these, light intensity showed the greatest association, followed closely by temperature. Essentially, the brighter and warmer it was, the more damselfly flights you see.
(Brief aside: Remember how I said last time that I didn’t agree with that Russian scientist who thought that barometric pressure was a major player in shaping odonate behavior? My results didn’t indicate that barometric pressure had any effect. This coupled with the fact that the Russian didn’t even measure barometric pressure in his study makes me skeptical of his results.)
So four weather parameters were important. The statistical test confirmed what I’d observed visually, that damselflies flew more readily in good weather than in poor weather. “Good” conditions were warm and sunny with little or no wind while “bad” conditions were cold, rainy, windy, and dark. I definitely observed pond abandonment behavior.
The most important question is this: what does all this mean? I think my data suggest two things:
1) The damselflies might be able to pick up on cues in the changing weather that alert them that a storm is approaching. Think about a damselfly, those big wings on a scrawny little body. If you’re a damselfly, it could be physically dangerous for you to be out in a storm. Being blown into the vegetation or the water could be deadly, heavy raindrops could impart a significant blow, and evaporative cooling could cause your body to cool down so fast that you can’t escape if the weather gets worse. Better to leave the pond before a storm than risk getting caught exposed in one. I think storms are dangerous to odonates, so the pond abandonment behavior that has been so often reported might be a means of protecting them from harm during bad weather.
2) Pond abandonment behavior might be related to roosting behaviors. Consider these ideas: Damselflies roost in sheltered areas away from the water at night. Storms usually result in a drop in the light level and temperature, which are the same things that happen as it gets dark at night. Damselflies disappear from the water before it starts to rain. It is therefore quite possible that pond abandonment behavior and simple roosting behaviors might be the same thing: odonates returning to their overnight roosts when it gets dark and cools down. It is likely also advantageous for damselflies to seek shelter during storms, but this could be a secondary benefit, something they gain by completing a behavior that has nothing to do with protecting them from storms.
Are odonates using weather cues to abandon ponds before storms? Or are they simply returning to their roosts because it’s getting dark? Are storms dangerous to odonates? These are some of the endless new questions I had after I finished this project and would like to answer. I had intended to study this behavior in more depth in grad school, but then I decided to attend grad school in Arizona. Colorado’s clockwork storms are perfect for studying these behaviors. Arizona’s wildly unpredictable storms are not. So, I changed my focus to the water bugs and have studied them ever since. I will go back to my beloved odonates someday though! I also decided a while back that my damselfly study was actually pretty unique and could make a real contribution to the scientific literature on odonates. Ten years after I wrote my undergraduate senior thesis, my data was published. If you’d like to read more about my study, look at some pretty graphs and whatnot, the citation is listed below.
I am dealing with some heavy things in my personal life at the moment, so I have no idea what I’ll do for the next few posts. I’m going to let myself be driven by whims for a week or two. I hope you’ll all check back to see where my whims take me!
Goforth, C. L. 2010. Behavioural responses of Enallagma to changes in weather (Zygoptera: Coenagrionidae). Odonatologica 39: 225-234.
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