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 boosted its positions in Whiting Petroleum Corporation (NYSE:WLL) and Vodafone Group (NASDAQ:VOD) significantly, while establishing a new position in Digital Realty Trust (NYSE:DLR).

Whiting Petroleum has been enjoying robust growth, thanks to operations in the Bakken region, and bulls see great potential in its Colorado Niobrara acres -- where its CEO reports a 400% internal rate of return on each drilled well. Its fourth quarter featured a loss due in part to rising costs, but it still met expectations. Year-over-year production grew by double digits, and proved reserves grew by 16%. Whiting expects production growth of 17% to 19% in the coming year. Analysts at RW Baird and the KLR Group boosted their opinions of the stock in February. It's Paulson's ninth-largest holding as of the 13F filing.

Vodafone Group has had an eventful past year, with shareholders approving the sale of its remaining stake in Verizon Wireless to Verizon for $130 billion. Among other things, that bolsters Vodafone's dividend, which is yielding 2.4%. The U.K.-based telecom titan is poised to profit from Europe's rebounding economy, and it's making further investments in Europe and other locations, such as India. Still, bears worry about threats such as the WhatsApp mobile device that permits people to communicate over the Internet for free. (Facebook just bought WhatsApp for an eye-popping $19 billion, making clear how much growth potential some see in it.) Vodafone's shrinking cash flow is another concern. The company is Paulson's second-largest holding, as of the 13F filing.

Digital Realty Trust, yielding a hefty 6%, invests in and operates data centers and is geographically diversified, too, with properties in the U.S., Europe, and Asia. Digital Realty Trust's fourth quarter featured operating revenue jumping 9% over year-ago levels and net income per share surging 43% between 2013 and 2014, with management noting "record leasing results for the fourth quarter and full-year 2013 driven by strong sales execution and large customer requirements to deploy cloud infrastructure and applications." Bears worry whether growth in supply will outpace demand growth in the industry, while bulls are happy about the company's ambitious stock buyback plans. They total up to $500 million, which is significant for a $7 billion company.

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Selena Maranjianwhom you can follow on Twitter, owns shares of Verizon Communications. The Motley Fool recommends Facebook and Vodafone. The Motley Fool owns shares of Facebook. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.