Fort Worth financier Robert M. Bass and his wife, Anne, were among the nation’s top 50 philanthropists for 2013 after making a $50 million pledge to Duke University, according to a report in The Chronicle of Philanthropy.Mark Zuckerberg, 29, and his wife, Priscilla Chan, were the most generous American philanthropists, with a donation of 18 million shares of Facebook stock, valued at more than $970 million, to a Silicon Valley nonprofit in December. The Chronicle of Philanthropy said the Zuckerbergs’ donation was the largest charitable gift on the public record in 2013 and put the young couple at the top of the magazine’s annual list of 50 most generous Americans in 2013.The second-biggest giver was the estate of George Mitchell, the late Houston oilman who pioneered drilling in the Barnett Shale. The founder of Mitchell Energy, which was sold to Devon Energy for about $3 billion in 2002, left about $750 million to the Cynthia and George Mitchell Foundation after his death in July.The gift to Duke from the Anne T. and Robert M. Bass Foundation ranked No. 42 on the list and will be used to establish Bass Connections, a program designed to encourage interdisciplinary study and collaboration between the university’s students and faculty, according to the Chronicle. Anne Bass, 65, has been a member of Duke’s board of trustees since 2003, and one of the couple’s children, Christopher, earned an undergraduate degree from the school in 1997.The Basses gave Duke $10 million in 1996. They made the Chronicle’s top giving list in 2005 with a $30 million gift to Stanford University, where Robert Bass, 65, earned an MBA in 1974 and Anne Bass earned a master of liberal arts in 2007, according to the school.In September, Robert Bass was estimated by Forbes magazine to have a net worth of $2.8 billion. He is president of the Keystone Group, an investment firm, and chairman of Aerion Corp.Lyda Hill, a Dallas granddaughter of the late oil tycoon H.L. Hunt, was ranked No. 35 for her $50 million pledge to the M.D. Anderson Cancer Center, a $7 million pledge to the Nature Conservancy, $4 million to the University of Colorado at Colorado Springs, and $2 to the Center for BrainHealth in Dallas.Other Texans on the list include John and Laura Arnold of Houston, ranked No. 5 after giving $235.9 million to the Laura and John Arnold Foundation. John Arnold founded Centaurus Energy, a hedge fund, and Laura Arnold is a former corporate lawyer. Also, Richard Kinder, chairman of Houston-based Kinder Morgan, and his wife, Nancy, gave $70.1 million to the Kinder Foundation. The top 50 contributors made donations last year totaling $7.7 billion, plus pledges of $2.9 billion.The Chronicle’s editor says the most significant fact from the list was the amount of money coming from living donors, which totaled about the same amount as the two previous years combined.“It’s a sure sign that the economy is getting better and people are getting a lot less cautious,” said the editor, Stacy Palmer.Some of the nation’s biggest givers do not appear on the 2013 list, not because they stopped being generous, but because their donations in 2013 were counted as pledges in previous years.For example, Microsoft co-founder Bill Gates and his wife, Melinda, gave their foundation slightly more than $181.3 million last year, but they were paying off a pledge of about $3.3 billion they made in 2004. CNN founder Ted Turner and Berkshire Hathaway Chairman Warren Buffett also made large gifts toward previous pledges.It took gifts totaling at least $37.5 million to make the list this year. Forty-two of the top 50 made gifts of $50 million or more.Thirty made big gifts to colleges and universities, but Palmer noted that most college gifts went to science and research this year, not to buildings, as in previous years. Ten of the 50 made the list because of bequests after their deaths. Ranked third on the list are Nike Chairman Philip Knight and his wife, Penelope, of Portland, Ore., who made a $500 million challenge grant to the Oregon Health & Science University Foundation for cancer research. Their pledge requires the university to match it within two years.No. 4 was former New York Mayor Michael Bloomberg, who made gifts totaling $452 million in 2013 to arts, education, environment, public health and other causes.Nineteen people or couples on the list have signed the Giving Pledge, started by Bill Gates and Warren Buffett in 2010. More than 120 of the world’s wealthiest individuals and families have pledged to give at least half their wealth to charity since the movement began.Although most people on the list are prominent wealthy people who have given generously in the past, Palmer said a few were surprises, including Jack MacDonald, a Seattle lawyer who gave $139 million to three nonprofits on his death. Staff writers Jim Fuquay and Steve Kaskovich contributed to this report, which includes material from The Associated Press.