Microscopy Image Gallery

Exploration of the Month

November 1998

cartoon turkey


At the end of this month, many of us will sit down with our families, give thanks, and eat one of the animals pictured to the left. The turkey is probably the most widely used symbol of the Thanksgiving holiday. Benjamin Franklin, a patriot from Revolutionary times, held the turkey in such high regard that he wanted to make it America's national bird! That title was instead given to the bald eagle.

Something all birds have in common though, is their unique characteristic of feathers. No other group of animals has these structures which are believed to have developed through evolution from the scales of their relatives, the dinosaurs. Feathers serve many purposes. They can be used to keep the bird warm, for flight, and to attract members of the opposite sex. Although they may seem simple in design, the composition of a feather is remarkably complex when observed with a microscope.

The rest of the page is divided into three sections. Each one examines a particular bird species and analyzes its feather composition. Certain sections of the feather will be shown to explain the feather's main purposes: insulation, flight, and decoration. All of the birds shown have one common factor; a portion of their feathers is iridescent. Iridescence is the ability to reflect normal white light into the visible color spectrum. Next to each bird picture, a sample of its iridescent feathers is shown. A thin beam of light was projected onto the feather's surface to get the proper reflection back to the camera. These pictures are slightly larger so the iridescence is easier to detect. Please have patience when the images are loading onto your screen.

blue-winged teal

blue-winged teal single teal feather

The blue-winged teal (Anas discors) is a type of duck found mostly around the upper Midwest, especially near the Dakotas. The two pictures of the solitary feather show how the color changes when light is projected from different places. Do you notice that the light gives the feathers a metallic shine?

Because birds like ducks spend an extraordinary time in water, they need protection from the cold. Down feathers insulate the duck to retain heat. They are fluffier in appearance than normal feathers and lighter in weight. The other two pictures below were taken with the scanning electron microscope. The appearance of a down feather is very different from that of a regular contour feather. The image magnified 10,000 times lets us see the surface of a single strand. Commercially, down feathers are stuffed into blankets and jackets so people can stay warm in cooler temperatures.

single teal feather down SEM 100X down SEM 10000X

common grackle

common grackle single grackle feather

The Common Grackle (Quiscalus quiscula) looks like a blackbird but is slightly larger. Grackles can be found almost anywhere in the Eastern United States. Parts of their feathers reflect light which looks green or purple. The closest analogy to their appearance might be if you've ever seen oil from a car mixed in a water puddle. The color in the puddle spreads over its surface, just like the myriad of colors on the feather's surface.

Birds need specific types of feathers in order to fly. They must be really strong to support the weight of the bird. The pictures below are of the grackle's contour feathers taken with the SEM. The center picture best illustrates the feather structure. The central branch coming down is called the rachis. The rachis is connected to the smaller projections called barbs. Finally, the barbs are connected to each other by the structures called barbules. The interlocking structure of each feather gives it strength. When a bird is flying, these hundreds of contour feathers enable it to push against the wind and propel itself forward. Do you think that birds can fly without feathers?

contour SEM 200X contour SEM 1000X contour SEM 4000X

ruby-throated hummingbird

ruby-throated hummingbird clump of hummingbird feathers

The smallest birds found in nature are hummingbirds. These remarkable creatures can fly sideways, backwards, and even upside-down! Ruby-throated hummingbirds migrate to most the Eastern United States in the summer. They are really fun to watch! This species is attracted to the color red and the sweet taste of flower's nectar. A good page which shows how to build your own hummingbird feeder is produced by Disney. Maybe you could attract them to your own backyard!

The brilliant feathers of a hummingbird are really small, less than a centimeter in length. Some individual ones have been isolated from the cluster in the above picture. Also above, you can see the difference between the red and green colors that the feathers reflect. Their main purpose is to attract female hummingbirds during mating season. By positioning their bodies in the sunlight, males hummingbirds "show off" to the females and get their attention.

SEM hummingbird 50X SEM hummingbird 250X SEM hummingbird 2000X

The pictures above show the section of the hummingbird's feather which is iridescent. The reflection is caused by tiny bubbles of air found underneath the wings' surface which are about 2.5 microns in diameter. As light enters these air bubbles, it is reflected as a different color. The color we see is dependent upon the size of the bubble and the amount of air it holds.

The pictures below illustrate the similar structure of the contour feathers. Its rough surface can be seen in the middle picture. In some of the images, little balls are spread throughout the feather's barbs. Upon further magnification, we can see that they measure about 2 microns in diameter. The dramatic magnification at 30,000 times shows us that these are probably small insect eggs which have been deposited on the hummingbird. This is a fascinating discovery, for we can observe how one species is dependent on another as it continues its life cycle.

SEM hummingbird 500X SEM hummingbird 3000X SEM hummingbird 30000X

Other Explorations

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Last Updated: 11/01/98