SAN JUAN, Puerto Rico (AP) – The number of Puerto Ricans identifying themselves solely as black or American Indian jumped about 50 percent in the last decade, according to new census figures that have surprised experts and islanders alike.

The increase suggests a sense of racial identity may be growing among the various ethnic groups that have long been viewed as a blurred racial mosaic on the U.S. territory, although experts say it is too soon to say what caused the shift.

“It truly breaks with a historic pattern,” said Jorge Duany, an anthropology professor at the University of Puerto Rico.

The growth in those calling themselves black or American Indian reduced the population share of Puerto Ricans who identify themselves solely as white. That group dropped nearly 8 percentage points to about 76 percent of the island's 3.7 million people.

More than 461,000 islanders identified themselves solely as black, a 52 percent increase, while nearly 20,000 said they were solely American Indian, an almost 49 percent increase.

Experts said several factors could have influenced the rise in the number of people who identify themselves as black.

Duany said the election of Barack Obama as U.S. president might have influenced some to call themselves black as the high-profile leader dispelled negative stereotypes about their race.

The jump in numbers of blacks also coincided with a push to highlight Puerto Rico's black population, with the Department of Education offering for the first time a high school book that deals solely with their history.

In addition, there was a grassroots effort to target dark-skinned Puerto Ricans through social media websites including Facebook that urged them to identify themselves as “Afro-Puerto Rican” in the 2010 census.

It was an option that appealed to Barbara Abadia-Rexach, a 30-year-old sociology and anthropology professor at the University of Puerto Rico.

On the 2000 census form, she and several relatives had reluctantly identified themselves as black or African-American.

“I don't identify with that although we are black Puerto Ricans,” she said. “But it is a formal structure, and we have to live with it.”

The island's population is a fusion of races where phrases such as “coffee with milk” abound to identify various varieties of skin color.

“There is no authentic or pure race,” Abadia-Rexach said. “We are all mixed.”

Puerto Ricans are known as “boricuas,” a name derived from the Taino Indian word for the island's indigenous people who were colonized by the Spaniards.

One possible reason for the increase in Puerto Ricans who identify themselves as American Indian is that the U.S. Census Bureau allowed responders to write down their tribe.

That was enough to get Naniki Reyes Ocasio to check the American Indian designation.

In previous censuses, the 63-year-old member of the United Confederation of Taino People refrained from picking that category. She didn't identify with being an American Indian since it did not include the word “Caribbean” in its description.

With the change, she traveled around with other Taino confederation members to show people how to complete the form and teach them about the new option.

“We can rewrite ourselves within history,” she said. “I used to check 'Other' because there was nowhere else I could place myself.”