A Little Bit More
The power that makes it possible for a bird to fly is concentrated in its pectoral or breast muscles. These muscles make up 15-25% of the total weight of the strongest flying birds. The Ruby-throated Hummingbird goes even further and has breast muscles that make up about 30% of its weight! Aerodynamics aside, it’s easy to see why humans will never be able to fly; our pectoral muscles are far too puny to provide the lift necessary to get our bodies off the ground.
The two types of muscles found in some birds are distinctly different in structure, function, even taste (any cook can tell you that there are differences in how they cook!). The red (dark) muscles are constructed of finer fibers than the white muscles. The darker color of the red fibers is due mainly to the presence of oxygen-carrying compounds that are absent or rare in white muscles. Red fibers also have a greater blood and fat supply. (If you’re watching your fat consumption, eat white meat rather than dark.) It’s interesting to note that a bird’s dark muscles, like our own, respond to inactivity by decreasing in size; the white muscles however, are not much affected by disuse, which is why our Thanksgiving turkeys have ample breast meat in spite of their flightless lives.
Activities
Move Over Arnold
Objectives: Close look at flight muscle attachment
Materials: Whole or part of turkey or chicken
Looking at Arnold Schwartzenneggar, one might think that his pectoral (chest) muscles must be large enough to provide enough strength for flight. Wrong – Arnold can’t begin to approach a bird’s strength. Actually, pound for pound, a bird is about 7 times as strong as a human. A close look at the skeleton of a bird tells the tale; the breastbone, where the pectoral muscles are attached, is huge in birds.
Cook a small turkey or chicken and bring it in to class for all to see. If you feel comfortable “dissecting” your bird in front of the students, they’ll be able to see the huge pectoral muscles as you slice off the breast meat. If you would rather not , you can always “dissect” your bird at home and bring in either the meat and breastbone or simply bring in the breastbone for examination. If you remove most of the meat from the breast bone, you’ll see the large skeletal area that the muscles are attached to – a graphic example of why birds have such powerful flight muscles.
Have you ever cooked or eaten a duck? You know that everyone says that they’re all dark meat. Well, ducks migrate and therefore have breast muscles that can function over long periods of time so they are made up of dark meat, no white.
Key Concepts
Adaptations and Diversity, Structures and Functions
Questions
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