African-Americans have become a shrinking presence in the boardrooms of the biggest U.S. companies in recent years, setting back a push by pension funds for greater diversity.

African-Americans, who make up about 13 percent of the U.S. population, account for 8.6 percent of the directors on the boards of the largest 200 companies by revenue in the S&P 500 in 2015, down from 9.6 percent in 2010, according to the annual Board Index study by Spencer Stuart, one of the largest executive search firms. The figure was 9 percent in 2006, the first year the firm reported the measure.

Reasons for the decline include the desire of boards to appoint members with particular qualifications such as cybersecurity expertise or a background in international business, headhunters said. Some African-American investors also said they worry the increasing influence of activist hedge funds – where the presence of blacks is minimal - in appointing board members is partly to blame.

"We're left out of these most lucrative parts of the economy," said John Rogers, chief executive of Ariel Investments, which manages $9.6 billion, and who sits on the boards of fast-food giant McDonald's Corp and electricity and natural gas utility Exelon Corp.

Rogers, 57, who is also a co-founder of the Black Corporate Directors Conference, a networking event, said he is frustrated by the lack of minority representation in some industries such as at big technology firms, in contrast to other companies like McDonald's itself, which counts three African-Americans among its fourteen directors.

"It's a tale of two cities," he said.

The dip in black boardroom representation comes at a time when many U.S. cities and college campuses have been split apart by protests over alleged discrimination and the deaths of black people in clashes with the police.