BOSTON, June 3 (Reuters) - William Ackman's Pershing Square Capital Management flagship hedge fund rose 2.9 percent in May, bringing it to a 22.1 percent gain so far this year and putting it ahead of most rivals, according to two investors in the fund.
Ackman, an activist investor, spent much of May pushing for pharmaceutical maker Valeant's $52.7 billion proposed acquisition of Botox maker Allergan. Pershing Square owns a 9.7 percent stake in Allergan, whose shares have risen more than 50 percent so far this year.
The gains help rank Ackman among this year's best-performing hedge fund managers, handily beating the average fund, which has gained only 0.83 percent, according to data from Hedge Fund Research. The performance also cements Ackman's own strong comeback from 2013, when his fund gained 9.7 percent but suffered bruising losses on J.C. Penney and Herbalife .
Pershing Square also held stakes in Canadian Pacific , Burger King Worldwide and Air Products and Chemicals at the end of March, according to a filing. (Reporting by Svea Herbst-Bayliss; Editing by Richard Valdmanis and Leslie Adler)