Although the Mardi Gras Indians have paraded on Fat Tuesday for more than 100 years, to many New Orleanians the elaborately dressed tribes remain mysterious, mystical, and even vaguely threatening.

"We're always afraid of something we don't understand," said Michael P. Smith, a New Orleans photographer and the author of "Spirit World," a book examining the rituals of the Mardi Gras Indians.

"But once people realize that the Indians are not any different from any other cultural or social organization, they realize that the myths that they are different are just that - myths."

Yet, Smith admitted, the Mardi Gras Indians have long fascinated locals and tourists alike because of their magnificently designed costumes rich in beadwork and feathers and their cultural traditions which seem to suggest practices and rituals from another place and time.

On Mardi Gras day tribes such as the Wild Magnolias, the Golden Blades, and the Red, White, and Blue parade on streets bordering downtown New Orleans - particularly on North Claiborne Avenue - dancing to tribal music and hand-clapping rhythms that remind many listeners of Calypso.

Parade watchers are inevitably struck by the splendor of the Indians' costumes: feathered headdresses that can tower more than four feet above a wearer's head, intricately beaded gowns and robes bearing the insignias of a particular tribe, individually drawn panels made of sequins and beads worn on the fronts and backs of gowns, representing a form of folk art.

But what is most fascinating about the Indians is what goes on in the months and weeks leading up to Fat Tuesday. According to Carolyn Kolb, the author of the Dolphin Guide to New Orleans, to be a member of a New Orleans tribe is a "commitment that can last all year."

"The rituals vary from group to group," Ms. Kolb said. "But usually there is one person who is the focus of a group and that person keeps it all going. Or perhaps one family is the focus, and they've been doing it for three generations or so."

Ms. Kolb said many of the tribes have "fragile arrangements" regarding organization structure and that there is no certain method of estimating how many Indian tribes are still active in New Orleans, much less how many people belong to each tribe.

"They might say they have a fixed number of people in each tribe," Ms. Kolb said, "but in practice they probably don't. Some tribes only count members as those who parade on both Mardi Gras and St. Joseph's Day and participate in tribal meetings throughout the year. Others count as members those who only participate infrequently or even those who march one time a year."

According to Smith, however, it is fairly certain that the actual number of active tribes in the city is on the decline. "There were maybe 15 or so active tribes a decade ago," Smith said, "but now there are large numbers of inactive tribes. Of the tribes that actually come out and mask for Mardi Gras it could be down to seven or eight."

One of the reasons for the decline of the tribes has been financial: in a city still suffering from a seven-year-old recession, tribe members, many of them on fixed incomes or working in jobs that pay minimum wage, have found it difficult to pay for costumes that can cost as much as $5,000.

In addition, some of the inactive tribes are made up of middle-aged and older members. As the older members die off, they have not been replaced in recent years.

Yet despite their diminishing numbers, the Mardi Gras Indians remain a highly visible presence in New Orleans on Fat Tuesday, attracting tourists and ethnic scholars from around the world. For those lucky enough to witness an Indian tribe chanting and parading through the streets of New Orleans, their majesty and ceremonial splendor presents a picture not soon forgotten.

Each tribe contains its own second line to march behind a parading brass band. According to Smith, the Indian second line was historically a freedom celebration. But in the 1870s, Spanish authorities, fearful that the Indians were summoning up voodoo powers with their chants, forbade the Indians to gather in public during the Carnival season.

By the early 1900s, however, the Mardi Gras Indians were regularly marching on Mardi Gras and soon formed the parade familiar to observers today - a procession that can stretch from five to 10 blocks followed by hundreds of onlookers who frequently fall in along the way to second line.

Oftentimes the tribes stop at certain corners to sing original songs, clap hands, and repeat in hypnotic fashion the lyrics to a tune. But when the parade continues tribe-sanctioned guards fall into place to protect the Indians' costumes - constructed with feathers, rhinestones, eggshells, paper-mache and colored glass - from the hands of curious onlookers.

Although many recent scholars and travel guides have suggested that the Mardi Gras Indians are an insular people sometimes hostile to picture-taking and interviews, Smith said the tribes are, in fact, very friendly.

"They aren't a secret society," he said. "They're just submerged, they're basically unrecognized, coming out of a repressed tradition."

The Mardi Gras Indians "are just ordinary people who are interested in carrying on traditional cultural and family values," Smith said.