Bill Ackman's hedge fund is roaring back from a recent losing streak. : Pershing Square is up 31.9 percent so far this year as of Wednesday, according to the New York-based firm's website. The solid returns follow a string of recent losses for the activist investor. In early 2018, the fund's assets were down by roughly half from their $20 billion peak in 2015. Pershing Square's net asset value dropped by 4 percent in 2017 while the S&P 500 rose nearly 20 percent that year. The fund firm suffered a high-profile, $4 billion loss on its stake in Valeant Pharmaceuticals.