There are approximately 85 species of birds in North America that nest in cavities. Some, like woodpeckers, excavate their own holes. Non-excavators like the purple martin nest in cavities previously dug out by other birds or animals. Then there are birds such as wood ducks that nest in naturally occurring cavities that form in many trees. Many of these birds will also nest in birdhouses provided by humans.

If you could travel back to a time before Europeans began coming to the New World, you could see these birds living in abundance, each filling a particular niche in the ecosystem. The birds ate bugs that might otherwise become a plague on woodlands. In turn, their numbers would be kept in check by hawks, owls, snakes, and other predators. It was a beautiful, healthy balance.

In a case of humans living inside their natural balance, Native Americans in some parts of the country discovered long ago that they could attract purple martins to nest in hollowed out gourds. In this case, the martins ate many bugs that were considered pests to people and animals. That is how the first purple martin birdhouse was created. (It is important to note here that, contrary to many claims, mosquitoes are not among the insects favored by purple martins.)

A more common example of human interaction with nature, in the last couple of centuries at least, can be examined in a discussion on "introduced species." Humans have frequently brought all kinds of plants and animals from their native lands, depositing them on foreign soil. Sometimes it happens accidentally, but there have been many intentional introductions as well. Many times, the new species dies out, because they were taken from their natural niche and inserted where there was no place for them. Occasionally, a species will survive, carving out a new niche. When this happens, it usually has devastating effects on native species.

In the bird world, two strong examples of successfully introduced species are the English house sparrow and the European starling. The house sparrow was brought to North America in the 1850's in an attempt to reduce insect populations around human communities. This, unfortunately, proved unwise. As the number of sparrows increased, they began to consume huge amounts of grain and growing vegetables, and they competed with native cavity-nesting birds. The intentions were good, but the experiment was simply ill conceived. The house sparrow aggressively defends any nesting site it claims, and these sites are often ones preferred by birds like bluebirds and purple martins.

If the introduction of English house sparrows to the U.S. was ill conceived, the case of the European starling was downright silly. In the 1890's, a man named Eugene Schieffelin wanted to bring to our shores every bird mentioned in the works of William Shakespeare. This comedy of errors ultimately culminated in the continental distribution of starlings. They now reside from coast to coast. Highly aggressive, they actually "evict" other cavity-nesting birds from their homes. This, combined with the ever-increasing pace of land development by humans, puts a great deal of pressure on our native bird populations.

Conservation is not a new or recent phenomenon. Conservation, or living in a sort of balance with nature, had been the norm for successful cultures for millennia. Many ancient societies had very respectful, and respectable, agricultural policies. Some were as simple as not over-killing, and using all parts of the animal for food, clothing, and shelter. Some early techniques were quite complex, like land terracing, crop rotation, and irrigation.

Then came the Industrial Revolution. Myriad products and services, such as the world had never before seen, suddenly came on the market, ever quicker and in greater numbers. The big businesses that grew up in this environment became very powerful; they felt they were invincible. They treated their workers horribly, they took advantage of consumers by gouging prices, and they ravenously devoured every possible natural resource in the name of profits. Forests, rivers, mountains, oceans, earth, and air all were hostage to the unrestrained avarice of the wealthy few.

Soon, a few wise observers realized that this was a trend with a dead end. In 1864, George Perkins Marsh, considered by many to be America's first environmentalist, wrote Man and Nature. In it, he argued that rampant deforestation would bring "the face of the earth to a desolation almost as complete as that of the moon."

Later, in 1892, a man named John Muir founded the Sierra Club, an organization that exists to this day. The first point in its mission statement is to "explore, enjoy, and protect the wild places of the earth."

Let us consider the words of another early proponent of conservationism, President Theodore Roosevelt. He said, "The conservation of natural resources is the fundamental problem. Unless we solve that problem, it will avail us little to solve all others."

Over time, information and awareness spread, and many groups and individuals stepped up to try to turn the tide of destruction. Today, there are thousands of organizations and millions of people worldwide that are dedicated to improving our ecological outlook. Environmentalism has become a persistent pint of our national and cultural discussion. It has been a big part of presidential campaigns ever since Teddy Roosevelt. It is as if we have always known how important our connection to nature is, but maybe we forgot for a while. Now, we struggle with the thought of sacrificing the life-enhancing things that technological progress has brought us. Though some sacrifices will be necessary, many knowledgeable people believe that they do not need to be big ones.

There are many things people can do in the course of their ordinary lives to improve the future of the ecology without making any sacrifices whatsoever. Picking up a new pastime - like birding, for example - could help make a positive change. Providing food, via bird feeders, and shelter, by way of birdhouses (also known as nesting boxes), for wild birds can actually help sustain native species. Bluebirds, purple martins, and wood ducks are a few species that are making comebacks thanks, in large part, to the efforts of recreational bird watchers.

Of course, there are a great number of organizations ready to help those new to the world of birding get started. From large national and international groups like the Audubon Society, the North American Bluebird Society, and the Purple Martin Conservation Association, to small, local birding clubs that can be found in towns of all sizes, help for the neophyte birder is close at hand.

We have traveled far in a dangerous direction. Only a major correction can steer us in the direction of a healthy, sustainable ecology, and preserve our beautiful world for coming generations. The good news is that a seemingly insurmountable task might be broken into millions of tiny, easy activities. If we are all together, each accepting a little bit of responsible stewardship of the earth, we can chart a course for success.