NEW YORK (TheStreet) -- Thanks to the controversy about Warren Buffett's most recently published New York Times op-ed piece, "Pretty Good for Government Work," many observers likely missed Berkshire Hathaway's (BRK.A - Get Report) recent 13F filing.

This quarterly document highlights the investing behavior of the Omaha native and Berkshire chief. Although Buffett has explained in the past that his favorite holding period for investments is "forever," he has been known to make interesting tweaks to his legendary portfolio.

Often, investors and market commentators can use these alterations to gain insight into his thoughts on the broad market and get clues about which sectors or companies have gained the Oracle of Omaha's approval.

Over the past three months, Buffett has been in a selling mood, shedding a number of positions entirely. This quarter's 13F saw the removal from Berkshire Hathaway's stock portfolio of companies including Iron Mountain ( IRM), NRG Energy, Carmax ( KMX - Get Report), Home Depot ( HD - Get Report) and Republic Services ( RSG - Get Report).

To Buffett watchers, the Omaha native's decision to drop Republic Services is peculiar considering its short time as a Berkshire holding. Additionally, his decision to unload RSG is interesting given the company's ties to friend, bridge partner and fellow billionaire Bill Gates. For a while now, the Microsoft ( MSFT - Get Report) founder has been accumulating a large stake in this trash company for his hedge fund, Cascade Investments.

The trash industry is not the first investment idea Buffett borrowed from Gates. For instance, years before Buffett made his famous all-in bet on the U.S. recovery by purchasing Burlington Northern Santa Fe Railroad, Gates boasted shares of another railroad: Canadian National Railroad ( CNI).

And although he didn't abandon them entirely, Buffett did reduce his stakes in a number of other Berkshire holdings including Procter & Gamble ( PG), Moody's ( MCO) and Nalco Holdings ( NLC).

Although he ended the quarter a net seller, Buffett did take time to make a few purchases. Most noticeably was his new position in Bank of New York Mellon ( BK).

The BK buy reflected his general optimism towards the financial industry. Berkshire's long-held Wells Fargo ( WFC - Get Report) position also saw an increase.

Lastly, the 13F indicated that Buffett added to Johnson & Johnson ( JNJ) and top holding Coca-Cola ( KO).

The increasingly defensive nature of Buffett's portfolio has been a theme touched upon on a number of occasions, and this most recent quarter once again brings this to mind.

However, beyond simple defensive positioning, Buffett's legendary portfolio appears to be becoming increasingly reliant on the performance of a small suite of major positions. Even prior to boosting his KO and WFC holdings, these two firms accounted for 40% of his portfolio.

As the billionaire investor prepares to hand over a portion of his portfolio to newly appointed Berkshire Hathaway chief investment officer, Todd Combs, it will be interesting to see what additional new changes are made.

In the end, despite Buffett's aggressive selling over the most recent quarter, it is unlikely the Oracle of Omaha has soured on the U.S. economy. As he made clear on numerous occasions, he stands by the belief that the nation is on its way to a slow recovery.

--Written by Don Dion in Williamstown, Mass.

At the time of publication, Dion Money Management had no holdings of equities mentioned.

This commentary comes from an independent investor or market observer as part of TheStreet guest contributor program. The views expressed are those of the author and do not necessarily represent the views of TheStreet or its management.