Vortex Stirs Up Sediment

photograph of white, grey and brown bird in water eating insects

Biological Strategy

Grey phalarope

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Image: Larry Lamsa / Flickr / Some rights reserved

Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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The spinning paddling behavior of phalaropes pulls sediment from the bottom of a pond for feeding by inducing an upward vortex.

Image: Mike Baird / Wikimedia commons /

Red-necked Phalarope, Adult breeding, 15may2007, Morro Bay, CA Estuary - handheld from an outrigger canoe

Image: Alan D. Wilson /

Red-Necked Phalarope (Male) , Wrights Pond, Malheur National Wildlife Refuge, Oregon

“Another way of using vortices to put edibles where they can be eaten underlies (literally) a peculiar behavior of phalaropes (noted as surface-tension transporters in the last chaper). A Phalarope spends much of its time in a single place on the surface of shallow water, spinning rapidly around its own body, as in figure 6.12b. According to Obst et al. (1996), the spinning represents the recoil of the peculiar paddling pattern with which it creates an upward vortex like a tiny, underwater tornado or water spout. That vortex brings up edible items, with barely a pause in the spinning the bird snags in its bill.” (Vogel 2003:136)

Red-necked phalarope feeding behavior

Last Updated August 18, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

Princeton University Press | 17/06/2013 | Steven Vogel

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