Total giving by the top 50 philanthropists in America dropped 30 percent last year, totaling $7 billion, and marking the lowest amount since 2010, according to a new report.

The Philanthropy 50 list, compiled by the Chronicle of Philanthropy, said the drop was partly due to massive one-time donations in 2014, including a $1.9 billion gift by Bill and Melinda Gates to their foundation.

Stock market volatility may also be to blame, especially with wealthy donors from Silicon Valley. After several years in which tech titans dominated the Philanthropy 50 list, New York and other regions made up the bulk of giving in 2015.

“For potential tech donors, the flat market in 2015 meant that there were fewer initial public offerings, mergers and acquisitions,” Emmett Carson, CEO of the Silicon Valley Community Foundation, said in the report.

The late billionaire Richard Mellon Scaife was the top charitable giver in the U.S. last year, with bequests totaling $759 million. Scaife, heir to the Mellon banking and oil fortune and a leading contributor to the Republican Party, died in 2014. His will was executed last year.

Scaife, who had lived in Pittsburgh, directed most of his fortune to two private foundations — the Allegheny Foundation, which supports charities in western Pennsylvania, and the Sarah Scaife Foundation, which funds conservative and libertarian public-policy groups. He gave each of these organizations $369.4 million.

Ranking second was the late John Santikos, who built the largest family-owned theater chain in Texas. Santikos gave $605 million from his estate to the San Antonio Area Community Foundation.

Ranking third was Michael Bloomberg, whose giving in 2015 totaled $510 million. He was followed by New York hedge-funder John Paulson, who gave $400 million to Harvard University. EBay founder Pierre Omidyar came in fifth and was the top-ranked tech giver on the list, with $327 million in giving.

Other notables included the Walton family, with founder Sam Walton’s three children giving $407 million in Wal-Mart stock. The Gateses gave $272 million to their foundation, while 48-year-old entrepreneur Jay Faison, who founded SnapAV, gave $165.6 million to promote clean energy. Warren Buffett’s sister, Roberta Buffett Elliott, gave $100.9 million to Northwestern University.

The 23 billionaires on the list gave an average of less than 1 percent of their estimated wealth. Of the 23, former hedge-fund manager John Arnold and his wife, Laura, gave the largest share of their fortune, at 5.6 percent.

The top 50 list only measures one year, so many donors, such as Gates, are giving away far more of their fortunes over longer periods of time. Whereas the Gates family donated just 0.4 percent of their $76 billion wealth last year, they’ve gifted $1 billion or more to their foundation several times.