Warren Buffett, the billionaire investor and famed Oracle of Omaha, saw the stock portfolio of his Berkshire Hathaway decline by about $2 billion in Q1, according to recent filings with the SEC. Given that the massive company still had a portfolio valued at about $189 billion as of the end of March of this year, though, that decrease represents a very small shift.

Buffett has long been known for picking his investments incredibly carefully and then standing by them over the long haul, and this past quarter was no different. The top five positions in Buffett's portfolio represent a whopping two thirds of the entire 13F investment package for the company. While Berkshire Hathaway did not enter any new 13F stock positions last quarter, Buffett did top up some of his long-standing holdings, including Apple Inc. (AAPL), Monsanto Co. (MON) and Teva Pharmaceutical Industries (TEVA).

Buffett Took a Big Bite of AAPL

As of the end of March, AAPL was the largest portfolio stake for Berkshire Hathaway, accounting for more than 21% of the company's investments, according to its 13F filing. Buffett waited until the first quarter of 2016 to buy the tech giant, but he has been increasing his position steadily since that time. In the first three months of the year, even as many other hedge funds were selling off shares of the iPhone maker on suspicion that it would not be able to sustain sales of its popular products, Buffett added about 45% to his existing position. Berkshire ended Q1 owning nearly 5% of all outstanding shares of AAPL.

Monsanto, Teva, US Bancorp and Others

While Buffett's position in Monsanto is much smaller than his AAPL stake, he nonetheless also added substantially to his MON position last quarter. Berkshire supplemented its holdings by nearly two thirds in the first months of the year. Similarly, TEVA stock was more than doubled last quarter, although it still accounts for less than 0.4% of Buffett's overall portfolio. US Bancorp (USB) occupies a slightly larger place in the list of Buffett's holdings, accounting for about 2.43% of his portfolio, according to Seeking Alpha. The position has been in existence for about 12 years, and Berkshire added marginally to it this last quarter. Other small increases include Bank of New York Mellon Corp. (BK) and long-time Berkshire favorite Delta Air Lines Inc. (DAL).

Although Buffett did not take on any new positions last quarter, he did sell out of two prior holdings. Graham Holdings Co. (GHC) was a very small position that was disposed of last quarter, and Buffett also liquidated his stake in International Business Machines Corp. (IBM). The billionaire has been selling IBM stock for several consecutive quarters and finally exited the position entirely by the end of March.