(Recasts with results of Jana and Greenlight; adds details on other funds and comparative performance to stock market)
BOSTON, June 1 (Reuters) - Prominent hedge fund managers David Einhorn and Barry Rosenstein both reported gains in May, signaling that some firms beat the broader stock market, which last month posted its best returns since January.
Rosenstein's Jana Partners fund gained 3.1 percent in May, with returns of 2.8 percent for the first five months of 2018, according to a performance report seen by Reuters. Einhorn's Greenlight Capital boasted a 3.6 percent gain last month, slimming his decline for the year to down 12 percent, also according to a report seen by Reuters.
The Standard & Poor's 500 index, a broad stock market gauge, climbed 2.16 percent in May and is up 1.18 percent in the first five months of 2018.
Most hedge funds are still compiling monthly returns, but Jana Partners and Greenlight traditionally report their numbers to clients hours after trading ends for the month. As a result, they are often bellwethers for hedge fund industry performance.
Preliminary data from Hedge Fund Research show that 2018 has been a mixed year for funds with the average firm inching up 0.20 percent last month and with a loss of 0.73 percent for the year-to-date. Final numbers for May will be released late next week.
Jana made headlines in April when it disclosed a 9.1 percent stake in Pinnacle Foods Inc, and it is urging the frozen food company to consider a sale. Pinnacle, which became Jana's biggest investment, in May gained 5.86 percent. Jeweler Tiffany & Co, another large holding for Jana, surged 27.18 percent.
Einhorn, meanwhile, bounced back a little bit after a run of disappointing returns that prompted many investors to pull billions of dollars out of his firm over the last years. In the first four months of 2018, Greenlight Capital lost 15 percent amid soured bets against companies including Netflix and Amazon.
Einhorn's performance got a boost on the last day of May when one of his biggest investments - General Motors Co - surged nearly 13 percent on news of a large investment in its autonomous-vehicle unit.
Eric Bannasch's tech-oriented Cadian Capital, which earned a 21 percent return last year, climbed 8.3 percent last month, for leaving it up 13.5 percent for the first five months of the year, according to numbers seen by Reuters.
(Reporting by Svea Herbst-Bayliss; editing by Jonathan Oatis and Leslie Adler)