Tuesday, August 30, 2011

Shadow Darner

Sunday evening I rescued this Shadow Darner from my bird net. Shadow Darners are common across northern North America. Among the largest and fastest-flying dragonflies, Shadow Darners prefer shady areas, usually near water. They fly into the late evening and sometimes even at night (Montana Field Guide). They also fly late into the fall. Already our evenings and nights have been cool, with temperatures in the 60s F.

Shadow Darners can take advantage of these cool climates, habitats, and times because they can regulate their body temperatures. A number of factors contribute to this phenomenon. When I removed the darner from the net, the dragonfly acted lethargic (as you can see as it perched on my finger). Later I placed the darner on a lily leaf. Here the animal began to quiver its wings, a behavior called "wing-whirring." Like shivering, this action can elevate the body temperature.  Furthermore, a darner can control heat loss by altering the circulation between its thorax and abdomen. Finally, large dragonflies like darners more efficiently retain body heat than do smaller ones (May 1976). When I returned from closing my nets for the night, the Shadow Darner had flown.

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