Five major acquisitions in the past four years have contributed to the high turnover rate among top executives at Bank of America (NYSE:BAC) , a company spokesman said.

"The level of leadership turnover we've experienced is consistent with the history of the organization and a consolidating industry," said spokesman Scott Silvestri.

But others worry that the 13 percent per year executive turnover rate has hurt the nation's largest bank, the Charlotte Observer reported Wednesday..

Bradford Bell, an associate human resources professor at Cornell University said a 5 percent a year turnover rate was enough to give some companies concern. Bank of America (NYSE:BAC) 's turnover rate "for top talent … is quite large," he said.

Acquisitions have contributed to the loss of 52 of the bank's 100 top executives leaving between 2005 and 2009. Former Merrill Lynch Chief Executive Officer John Thain, former President Greg Fleming and former wealth management head Bob McCann all left soon after the purchase closed in January.

Many of U.S. Trust's executives, including CEO Peter Scaturro and successor Frances Aldrich Sevilla-Sacasa, left after the firm was acquired, which contributed to U.S. Trust's fall from No. 3 in the Luxury Institute's annual ranking of brand prestige to No. 35 this year, the newspaper said.