His personal quest for a great print of Carolina Parakeet took nine years. As a student, he spotted the image at a gallery in Washington, D.C., and immediately fell in love with it. Kattner did not have the funds to buy it, but he vowed to someday own the print. Four or five years later, he had the discretionary income, but no high-quality copy was available. He settled for a slightly damaged copy, and then waited several more years to trade that one to Oppenheimer for a better version at a higher price. "With Audubons, it’s all about buying the top piece. Those usually accelerate in price, and there’s always a market for them," Kattner says.

Peter Cowen developed a love for Audubons 35 years ago when he was a journalist researching art for an article. As often happens with the works of Audubon, the discovery of the prints led to a purchase, which then ignited a passion for the famous double elephant folio birds. Realizing their financial potential, Cowen switched careers and became a private dealer based in Newton, Mass. While there are intermittent slow periods when the prices level off, Cowen says the Audubon business has been notable for remarkably consistent price appreciation.

AUDUBON’S GENIUS was in showing birds, such as American Flamingo, in their natural state.

Cowen, who has owned and sold most of Audubon’s important images, as well as many smaller birds, saw revenues spike during the second half of 2005. He says that the market has adjusted to recent price increases, including the record-setting sale of an American Flamingo for $197,900 in 2004 at Christie’s. Cowen believes there are some undervalued double elephant prints, such as the colorful Painted Bunting or some of the warblers that are surrounded by beautiful flowers.

But he remains cautious about any collector putting financial return ahead of aesthetic value. "I honestly believe that people who buy because they love the prints, and pick images they love, will make the best investment," Cowen contends. "People always say that, and then they don’t always do it. If you buy something you don’t love because some dealer told you it’s a great investment, you’re making a huge mistake; you might as well put it in T-bills."

Sidor has chosen to build his collection thematically, focusing on birds from the tall-grass prairies of the Midwest where he grew up, as well as extinct species. Even after years of study and appreciation, Sidor still spends hours contemplating the images–perhaps the most fitting tribute to Audubon’s work. "I’ve had a lifelong interest in birds," says Sidor, adding that he cannot list his favorite Audubons because he loves each one in his collection. "I really just enjoy looking at them."

Catherine Curan is a New York-based freelancer who writes about business, culture and style.

Photographs courtesy of Christie's.