Transverse waves are generated at two locations: the bow (front) and the stern (back) of the duck. As they superimpose in the wake, these two waves can either interfere\u00a0constructively to produce large waves (producing a maximal drag), or interfere destructively to cancel one another (producing a minimal drag). Which happens depends upon the speed of the duck and so is under the duck’s control. Of course, the Hooded Merganser does not calculate this, but rather senses the effort it takes to move and so travels at\u00a0a speed that minimizes its wave drag.<\/p>\n
While divergent waves remain, the hoodie’s transverse waves have been substantially canceled.\u00a0
\n![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2021\/03\/hoodedmerganser210309s.jpg\")
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Flying<\/b> Parasitic drag results from energy lost to turbulent eddies shed by objects moving rapidly through the air, such as a runner, automobile, train, bird, or aircraft. Parasitic drag increases as the square of the speed.<\/p>\n Induced drag is equal to the force required to provide lift and results from the change in direction of air flow around a wing which supports the weight of the flying object. Induced drag changes inversely with the square of the speed.<\/p>\n So, one type of drag increases with flight speed, the other decreases with flight speed. At some speed, the sum of the two drags has a minimum value: an optimal flight speed. Birds, including Hooded Mergansers, tend to fly at (or near) this optimal speed because it minimizes the energy required for flying.<\/p>\n However, the Hooded Merganser has an additional consideration: its hood (crest). Parasitic drag is proportional to the forward-facing cross-sectional area of the bird, and that area would include the hood if the bird were to keep it erected, so the bird collapses its hood when flying.<\/p>\n The hoodie collapses its hood (see previous picture) to minimize parasitic drag when flying. While both of these behaviours — minimizing wave drag when swimming, minimizing parasitic drag when flying — easily pass unnoticed; each is crucial to the duck.<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Much of bird watching involves creature identification, along with tracking seasonal migration. However, this posting is about neither of these; rather, it treats obscure behaviours of a duck, the Hooded Merganser. The issue is that of the duck optimizing … Continue reading
\nFlight involves two major forms of drag: parasitic<\/em> and induced<\/em>.<\/p>\n
\n![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2021\/03\/hoodedmerganser210309as.jpg\")
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