The Valeant investment has hurt Ackman, and his Pershing Square Holdings fund has lost 21 percent so far this year. Peltz' Trian Partners is roughly flat.
On average, activist funds lost 0.38 percent in the first half, according to data from Chicago-based Hedge Fund Research.
Activists' cash pile is also smaller, with assets at $112.5 billion at the end of the first quarter, down about 8 percent from $122.9 billion on Dec. 31, 2015, according to HFR data. In the first quarter investors pulled out $4.3 billion, a shift from the record $14 billion they added in 2014.