Sadly, few amateurs can devote years of their lives to fieldwork. But that doesn't mean enthusiasts cannot make important contributions. Thousands have already joined the ranks of urban naturalists, studying species that live quite literally in their own backyards. A few have even distinguished themselves by developing new methods to uncover nature's secrets.

To this short list of distinguished amateur naturalists, we can now add an ophthalmologist from Omaha. Robert Slaughter has developed an ingenious method for spying on house sparrows. He combined a birdhouse, a camera and a blind in one unit to get close-within a foot or so-to a brood of nesting birds. The method opens up new vistas for investigating animal behavior.

The idea is simple. Slaughter modified a standard birdhouse, removing the top and extending the sides. He next cut an observation port in his elevated wooden patio deck and mounted the birdhouse underneath the deck so he could peer down into the chamber. (Deckless amateurs take heart-you can adapt this project with a video camera, as I'll explain later.) An old magician's trick enables Slaughter to view the birds surreptitiously. The entire arrangement lets him make detailed observations of nesting birds, day or night.

The magician's trick requires a black veil thin enough to see through easily. It is stretched across the open top of the birdhouse. By lighting the interior of the birdhouse, a naturalist can see the goings-on inside the nest. In Slaughter's device, the fabric is mounted on a sliding frame to allow a fresh section to be moved into place whenever material from exuberant nest building adheres to the fabric and obstructs the view.

The birds will not sense that they are being watched as long as the observer remains in darkness. To accomplish that, Slaughter built a blind (basically, a small tent) that completely enclosed the observation area. The frame, which was made from plastic polyvinyl chloride (PVC) pipe fittings, can house two people. He draped the frame with "blackout" cloth purchased from a neighborhood fabric store and covered the cracks between the floorboards of the deck with opaque tape. You can also place aluminum foil over the cracks and seal it in place with duct tape.

Although the blind technique works well, you may want to consider less ambitious (and less costly) strategies. A hood similar to those used to cut down glare on oscilloscope displays should do nicely; you will also need some additional black cloth to keep out the light when you are not observing. Alternatively, you can permanently affix a 35-millimeter, single-lens reflex camera just above the hole. Amateur ornithologists may then watch the birds directly through the viewfinder of the camera without having to conceal themselves. Whatever you do, make sure that rainwater cannot leak into the nest and, more important, that a cat or other predator cannot get in. When not observing, Slaughter protected his subjects by turning a plastic washbasin upside down over the observation port and securing it with bungee cord.

The interior lighting is critical. A bulb inside the birdhouse would overheat it, so Slaughter illuminated the nest from the outside. He first painted the nest's interior white to minimize shadows. Then he cut into the back of the box a rectangular slot one and a half inches wide, three and a half inches long and six inches above the bottom of the nest chamber. To diffuse the light and illuminate the nest evenly, Slaughter covered the slot with a piece of opalescent glass. A thin sheet of white plastic would serve the same purpose.

Almost any light source is suitable so long as it is weatherproof. Slaughter used low-voltage yard lights available from local hardware stores. The brightness of the lights can be controlled by wiring in a dimmer switch. To reflect more light into the box, he placed a white board behind the lights.

Slaughter sent me some wonderful photographs taken from his ornithological observatory. He gets good depth of field using a flash and a 100-millimeter macro lens with its f-stop set at 32. The problem was directing enough light from the flash into the birdhouse. Slaughter removed the flash from his camera and positioned it over a hole he cut in the side of the birdhouse. He triggered the flash with a short cable purchased at a camera store. Slaughter reports that, oddly enough, the flash does not seem to bother the birds.

Nifty as this setup is, the project could be developed into an even better scientific tool. Consider, for example, how to automate the observing process, quantify the activity in the nest, record the weights of the birds throughout the nesting season or monitor the temperature of the eggs during incubation. Any of these additional endeavors would make a great amateur project.

To get you started, let me suggest a way to record your observations of the nest continuously. Try replacing the still-photography camera with a small video camera. It can continuously record the movements in the birdhouse, and the signal can be piped directly into your television or videocassette recorder. That way, you can observe your subjects comfortably in your own home. It's also a dandy solution for amateurs who do not have a wooden patio deck: you can mount the birdhouse wherever your subject roosts. Also, many camcorders can detect near-infrared light. A bright infrared-light-emitting diode may be able to illuminate the inside of your birdhouse and allow clear videos to be shot at night without disturbing the birds.

It may be possible to quantify the activity inside the nest using an ultrasonic motion sensor. Such devices can be cannibalized from old burglar alarms. Position the sensor next to the camera and point it down toward the birds. If they do not flee when the sensor is turned on, they probably can't hear the ultrasound.

The fraction of time the sensor spends in its triggered mode is a measure of the birds' activity. You'll need to experiment with both the intensity and sensitivity levels of the sensor. You will also need a chart recorder or a computer to monitor the signal. Data recorded 24 hours a day throughout the nesting season could reveal fascinating tidbits about avian behavior. The sensor can also alert you when the birds enter or leave the nest or set off your photographic equipment.

Keep in mind that improving these techniques could allow you to answer several open scientific mysteries. For instance, a house sparrow typically lays a clutch of four eggs, one each day for four days, and so the first egg is usually three days older than the last. Yet all the eggs hatch within about 24 hours of one another. Perhaps the nesting bird positions its body to warm new eggs more efficiently than the older ones, so the warmer eggs develop faster. Measuring the eggs' temperatures when the birds leave the nest may answer this question. Let me know what you discover with this or any other variation.

For more information about this project, including suggestions for fascinating ornithology experiments, send $5 to the Society for Amateur Scientists, 4951 D Clairemont Square, Suite 179, San Diego, CA 92117 or download the information for free from the SAS Web site. You can also post messages about this or any project on the SAS Web site.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.