Every quarter, fund managers have to disclose what they've bought and sold. Their latest moves can shine a bright light on smart stock picks.

Today let's look at investing giant Bill Ackman, who founded Pershing Square Capital Management in 2003. An investor with roots in real estate, Ackman is an activist, often advocating strongly for big changes at companies in which he has invested heavily. Soon after Ackman invested in the Fortune Brands conglomerate, for example, the company began looking to spin off various divisions -- which it has now done, breaking up into the alcohol-focused Beam and Fortune Brands Home & Security (NYSE: FBHS).

Pershing Square's portfolio totaled $7.8 billion in value as of Dec. 31, 2011, spread over just 10 stocks. Now that's concentration! Its top three holdings, Canadian Pacific Railway (NYSE: CP), J.C. Penney, and General Growth Properties, make up a whopping 52% of the portfolio's total value.

Interesting developments
So what does Pershing Square's latest quarterly 13F filing tell us? Here are a few interesting details:

Well, there was only one new stock on the list, and it was Fortune Brands Home & Security. The fact that fellow Fortune Brands spinoff Beam, the liquor company, isn't among Pershing's holdings suggests that Ackman either saw more value in the security arm of the company or perhaps that he simply thinks it's a better bargain these days. After all, many housing-related companies are rather beaten down, waiting for the eventual housing recovery to revive them.

The only holding that saw the number of shares held increase was Canadian Pacific Railway, and boy, did they increase, by nearly sixfold. Ackman is reportedly advocating a CEO change, trying to bring in Hunter Harrison, who retired from Canadian National.

Two companies saw a significant decline in number of shares held -- Kraft (NYSE: KFT) and Family Dollar (NYSE: FDO). It can be argued that these are defensive stocks, holding up well in tough economic times as consumers tighten their belts -- and that they may not perform as well as our economy rebounds and people start to spend more on food and other items. Of interest to many investors, Kraft is splitting itself up, dividing its North American grocery business from its global snack business. Family Dollar, meanwhile, made many investors happy with a 17% dividend increase recently.

Finally, only one company was eliminated from the roster during the quarter, and that was Lowe's (NYSE: LOW). Some investors like its growing attention to online sales, via its acquisition of ATG Stores, but others weren't thrilled last year as the company announced store closing and pared back its expansion plans.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13F forms can be great places to find intriguing candidates for our portfolios.

Looking for promising investments? Check out our free special report -- " The Stocks Only the Smartest Investors Are Buying " -- and learn which stocks are appealing to Warren Buffett and other great investors.