Applying wind tunnel studies and aerodynamics to movement ecology

Background/Question/Methods

Biologists have historically used wind tunnel studies to measure biomechanics and fluid dynamics of flying animals (birds, bats or insects) and plant seeds. The advantage of a wind tunnel study is that it simplifies the complexity of the natural environment, allowing for repeatable and controllable measurements. Using two studies, we demonstrate how wind tunnel investigations and flow diagnostics can be applied to conservation-related problems. In our first study, we measure the kinematics and aerodynamics of prairie plant seeds to investigate seed dispersal mechanisms. To quantify the dispersal potential of different prairie plant seeds we recorded high-speed video to analyze kinematics of seeds and we used particle image velocimetry to visualize the aerial footprint of seeds in a vertical wind tunnel. Our second study looks at the temperature dependence of butterflies in the context of habitat edges. To investigate the sensitivity of butterflies to environmental parameters, we allowed butterflies to fly freely in a wind tunnel that was divided into two parts, with one environmental variable (in this case temperature) varying between the two parts. An identical food source in each compartment was provided and the butterflies’ preference was recorded, and analyzed.

Results/Conclusions

Seed dispersal ability of native seeds can improve restoration efforts, while non-native and weed seeds can threaten both native landscapes and crops. Our results show that non-plumed seeds tend to spin and rotate, and are highly unstable in the airflow, while plumed seeds are very stable. Some plume designs are aerodynamically more robust than others.  Dandelion seeds show a continuous wake structure, while others, (e.g., false boneset), show vortex breakup. These differences could explain why dandelion seeds tend to disperse further and are more common and widespread than native prairie plants.

Some grassland butterfly species show differential probabilities of crossing habitat edges between different land cover types. In highly fragmented landscapes, these behavioral responses to edges could influence butterfly dispersal and thereby affect population isolation. One reason for this edge response could be a temperature change between land cover types. Our results show species-dependent temperature preferences. Some species (e.g., Papilio lowii) had a significant preference for the warm side of the wind tunnel, whereas others (e.g., Papilio polytes) showed a significant preference for the cold side. These results validate our technique, providing a basis for future research to understand the underlying reasons for butterfly responses to habitat edges.