A Little Bit More
Almost everyone knows that ducks have webbed feet, that’s a no-brainer! But if you ask almost anyone what other birds have done to accomplish a similar adaption, they may have trouble answering. We discussed convergent evolution in an earlier unit called Roads Converge, and we can see this same process in action with waterbird feet. Each of the four kinds of birds depicted on this unit poster has arrived at a similar “solution” that makes it possible for them to navigate easily in water. These aren’t the only kinds of birds that have made a similar adaptation but these four are reasonably common ones used to illustrate my point.
It’s interesting to note that while a bird may have adapted its feet to maximize efficiency in water, this same adaptation may reduce its efficiency with perching or walking, for example. Pelicans and ducks can certainly perch, but are not very good at it with those “big, floppy feet”. Special adaptations for life in water must be pretty important and obviously take precedence over perching for these birds. Guess you could say that some adaptations are not 100% positive!
Activities
Science – Making Waves
Objectives: See firsthand how webbing helps with swimming
Materials: Thin-tined serving fork, bucket or sink of water, sandwich bag and rubber band
It’s not too difficult to imagine how the webbing on a waterbird’s foot can improve its swimming efficiency. After all, anyone who has ever watched a scuba diver knows they use fins to improve their swimming ability. But sometimes it helps to have a concept reinforced and that’s what this exercise can do.
- Take a thin-tined fork (a serving folk will probably be larger and better for this exercise) and move it quickly through a container of water using its broad side like a paddle. You can have an individual student perform this or ask each student to give it a try. You should be able to get a sense of both the resistance it takes to quickly move the fork through the water, as well as, note the wave or splash that is creates when you do so
- Now tightly wrap the lower portion of your fork with a sandwich bag so your fork is basically the same size but the spaces between tines are no longer open (this is our “webbed foot”).
- Again move the covered fork through the water at the same speed/strength and note both the resistance as well as the wave it creates.
- The difference between the resistance and wave created between the uncovered and covered forks won’t be all that great but it should be different enough for your students to notice that it has some forward propulsive value.
For animals living a great deal of their lives in water, having webbed toes really does make a big difference in the efficiency they can expect.
Why is efficiency of swimming important, anyway? The more efficient an animal can be getting around in its habitat, the less energy is needed. Energy conservation is always important for an animal that can’t guarantee when it will find its next meal. The more efficient an animal is, the more likely it is to survive; simple as that!
Key Concepts
Structures and Functions, Adaptations and Diversity
Questions
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