The latest 13F season is commencing, when many money managers issue required reports on their holdings. It can be worthwhile to pay attention, as you might get an investment idea or two by seeing what some major investors have been buying and selling.

For example, consider Paulson & Co., founded in 1994 by investing giant John Paulson. Owned by its employees, the company has specialized in merger arbitrage, among other things, profiting when one company buys or merges with another (or merely announces plans to do so). It has grown into one of the largest hedge fund companies in the world.

Paulson's latest 13F report shows that it reduced its positions in MGM Resorts International (NYSE:MGM) and Pioneer Natural Resources Company (NYSE:PXD), and sold off all its shares of FedEx Corporation (NYSE:FDX).

MGM Resorts International has become the hottest company in Las Vegas and also has considerable operations in the immense and growing Macau market. (Gambling revenue in Macau grew 40% in February and it takes in more than six times the revenue as Las Vegas.) In its fourth quarter, MGM Resorts posted revenue up 10% over year-ago levels and $330 million in consolidated operating income, compared with a $425 million loss last year. MGM China is doing particularly well, with fourth-quarter revenue up 27%. The company is looking to expand in Japan, but some wonder whether its debt burden will get in the way.

Pioneer Natural Resources has investors excited about its future, stating that it's sitting on more than 7 billion barrels of recoverable oil and gas in the Permian Basin, and it's doubling down on its Eagle Ford operations. Fool analysts have suggested that it might be operating in the best oil field in the country. Its fourth quarter saw it producing 164,000 barrels of oil equivalent per day, up 8% from year-earlier levels, while "targeting compound annual production growth from continuing operations of 16% to 21% for 2014 to 2016 and expecting to more than double production by 2018 compared to 2013." Still, Pioneer's stock price may have gotten ahead of itself a bit, leaving little margin of safety.

FedEx took some hits during our recent recession, but the company is turning itself around. It's cutting costs, hiking ground and home delivery rates by 4.9% and freight rates by an average of 3.9%, and it has introduced flat-rate express shipping. FedEx's last quarter featured profits up 14% and management upping projections. It is also rewarding shareholders by buying back up to about 10% of its shares. It's expanding internationally and stands to benefit from increased online shopping, too.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.