LONDON (AP) — A pair of U.S. philanthropists with a passion for wild cats pledged Friday to match new donations to Oxford University's Wildlife Conservation Unit — the researchers who were tracking the movements of Cecil the lion in Zimbabwe.

Tom Kaplan, a natural resource investor whose net worth was put by Forbes magazine at $1 billion, and his wife, Daphne, will match donations made after 3 p.m. London time (1400 GMT) Friday up to a total value of $100,000. The Kaplans hope to help the Oxford researchers raise half a million pounds to further their work.

"We have to seize this moment where we can all make a difference," Tom Kaplan said in a statement, adding that if the "death of Cecil can lead to the saving of many more lions, then some good can come from tragedy."

The pledge comes hours after Zimbabwe said it would seek to extradite an American dentist who lured the lion out of a national park and killed him.

The death of Cecil, a well-known resident of Hwange National Park, has touched off international outrage and sparked a worldwide conversation as to how to best safeguard the dwindling number of big cats.

Oxford's WildCRU, one of the world's top university research groups, tracks the movements of hundreds of lions and runs an anti-poaching team. It also works with local farmers to help them live alongside the lions. It had followed Cecil's movements in minute detail since 2008.

Kaplan, a former student at Oxford who made a fortune in metals, is also the chairman of Panthera, a foundation dedicated to the preservation of wild cats.