The world’s biggest mutual fund keeps getting smaller.

Bill Gross’s Pimco Total Return Fund shed $41 billion, or 14 percent of its assets, in the past four months through losses and investor withdrawals. The fund suffered $7.7 billion in net redemptions in August, Chicago-based researcher Morningstar Inc. said today in an e-mailed statement, the fourth straight month of withdrawals.

Investors have been fleeing bond funds since May, when Federal Reserve Chairman Ben S. Bernanke first raised the possibility that the central bank would begin to scale back asset purchases. The yield on the 10-year U.S. Treasury note has risen to 2.86 percent today from 1.93 percent on May 21, the day before Bernanke spoke.

Over the past four months, investors redeemed $26.4 billion. The fund lost 3.9 percent this year, trailing 86 percent of peers, according to data compiled by Bloomberg.

An e-mail and phone call to Mark Porterfield, a spokesman for Pacific Investment Management Co. in Newport Beach, California, wasn’t immediately returned.