Vol. 43, No. 4
David M. Larson
Rock Pigeon. Photograph by Martin Cathrae (CC BY-SA 2.0).
The natural world is a messy place to get around in. Vegetation, rocks, and water bodies are all obstacles if you are flying around low. And then you have to deal with man-made obstructions. Surprisingly, for all we know about bird migration, we know little about short-range navigation in birds and how they deal with obstacles. How does a Cooper’s Hawk blast through a forest at top speed on a hunting run? How do Barn Swallows land on a power line? Do these birds plot their courses far ahead as they fly or do they rapidly adapt to obstacles in their path?
Williams and Biewener (2015) have begun to tease out some of these questions of flight strategy by studying Rock Pigeons (Columba livia) flying along a corridor from one perch, through an array of vertical posts, to another perch. Distances between the posts were adjusted from 13–26 centimeters (5.1–10.2 inches), corresponding to 20–40% of the birds’ wingspans. The pigeons successfully traversed the barrier of posts in more than 95% of attempts, although adjusting the gaps to less than 13 centimeters greatly increased refusals by the birds. Flight dynamics were recorded with high-speed digital video as the birds flew through the barriers. In order to analyze flight parameters from the recordings, small infrared light-emitting diodes powered by a harness battery pack were affixed to the birds on the head, back, and at two places on each wing (near the tip and at the wrist). These light sources, undetectable by the birds but clearly detectable on the video recordings, provided spatial information for computerized analysis of the videos.