It was a timely move by the investor's Soros Fund Management. On Tuesday, the U.S. Justice Department filed a lawsuit to block the proposed merger of US Airways and AMR Corp, the parent company of American Airlines.

Other regulatory filings from hedge funds and investment firms showed Leon Cooperman's Omega Advisors soured on Facebook Inc in the second quarter, but Patrick McCormack's Tiger Consumer Management took a shine to the social networking company.

So-called 13F filings with the U.S. Securities and Exchange Commission offer a window into the strategies of money managers when it comes to buying and selling U.S. stocks.

Omega, for instance, in the quarter sold 3.67 million shares of Facebook, according to the firm's regulatory filing. The hedge fund also took a new stake of 5.72 million shares in New Residential Investment Corp, a mortgage real estate investment trust.

Tiger Consumer added 1.2 million shares of Facebook, bringing its total holding to 4.8 million shares. The hedge fund also raised its position in struggling retailer J.C. Penney Co to 5.4 million shares, from 3.37 million at the end of the first quarter.

U.S. securities regulators require managers to include their U.S. stock holdings on a 13F filing four times a year.

Small investors seeking to mimic the actions of big money managers should be wary because the filings are merely a snapshot of how a top hedge fund's stock holdings looked 45 days earlier. These filings do not reflect more recent buying or selling activity by a fund.

Here is a capsule summary of some of the top managers' filings for the second quarter.

SOROS FUND MANAGEMENT

Billionaire investor George Soros bought 5 million shares of Herbalife during the second quarter, and the position now makes up 2.5 percent in his own portfolio.

ELLIOTT MANAGEMENT

Paul Singer's hedge fund raised its stake in buyout target Dell Inc to 22.4 million shares, from just 516,000 shares in the first quarter.

Eton Park

Eric Mindich's Eton Park hedge fund jumped into Sprint Corp, previously Sprint Nextel Corp, with a 13 million share position in the second quarter. The fund also substantially increased its stake in News Corp, to 17 million shares from 5.75 million at the end of the first quarter.

COATUE MANAGEMENT

Philippe Laffont's Coatue increased its stake in Apple Inc from some 400,000 shares to 1.6 million shares. The fund cut its position in Green Mountain Coffee Roasters by 2 million shares, leaving it with roughly 3 million shares at the end of the second quarter.

FARALLON CAPITAL MANAGEMENT

The San Francisco based hedge fund, like Eton Park, also took a big stake in Sprint in the second quarter, reporting a new 13.8 million share position. The fund, founded by Thomas Steyer, sold all of its 2.9 million shares in snack food manufacturer Mondelez International Inc.

The fund also lifted its position in Dell to 16.8 million shares from 2.4 million shares at the end of the first quarter.

OMEGA ADVISORS

Leon Cooperman's hedge fund joined Farallon and Eton Park as buyers of Sprint stock in the second quarter, adding 30 million shares to raise its stake to 95.1 million shares.

PERSHING SQUARE CAPITAL MANAGEMENT

Bill Ackman's hedge fund exited its 5.9 million share stake in Mondelez in the quarter.

THIRD POINT

Dan Loeb's hedge fund got rid of its stake in the SPDR Gold Trust in the second quarter, as well as its interest in Delphi Automotive, which had been one of the hedge fund's largest holdings. Meanwhile, the fund opened a new 1.7 million position in Tiffany and Co.

TIGER GLOBAL MANAGEMENT

Chase Coleman's New York-based firm got rid of its stake in J.C. Penney in the second quarter, and dumped Apple. Coleman also joined Mindich in liking News Corp, increasing the fund's holding by 74 percent to 15.7 million shares.

TRIAN FUND MANAGEMENT

Nelson Peltz's Trian took a new 5.8 million share stake in DuPont Co. The fund also opened a new 2.1 million position in Sotheby's.

(Reporting by Katya Wachtel, Svea Herbst-Bayliss, Samuel Forgione and Ben Walsh; Compiled by Matthew Goldstein; Editing by Edwina Gibbs)

By Katya Wachtel and Sam Forgione