Investor Warren Buffett made his annual gift of Berkshire Hathaway stock to the Bill & Melinda Gates Foundation Wednesday. At $1.25 billion, the value of the gift is 30 percent less than last year's contribution of $1.8 billion.

Buffett donated 428,688 shares of Class B Common Stock to the Gates Foundation in 2009 as part of his lifetime pledge, described here.

Under Buffett's plan to transfer the majority of his wealth to the Gates Foundation, the timing of the annual gift and the amount of shares are predetermined. But the value fluctuates.

According to the schedule, the number of shares donated diminishes by 5 percent each year. Buffett had expected the value of his shares to increase by an amount that more than compensates for their smaller number. And for the first two years, they did. CNBC's coverage has a chart of the annual gifts here.

But even shrewd investors have not escaped the wrath of the global recession, and Berkshire Hathaway has seen the price of its Class B shares decline by about 26 percent over the past year. Those shares closed at $2,924 a share on Wednesday.

Forbes estimated Buffett's net worth at $37 billion this year, ranking him second only to Bill Gates (whose worth was estimated at $40 billion) in the list of the richest people in the world.