Tonight's Instant Index: Image credit: Kevin Winter/Tonight Show/Getty Images Here is some potentially startling news about a giant in the world of late-night television, Jay Leno. The Hollywood Reporter is quoting two high-level industry sources that NBC may be pushing Leno out of his chair on "The Tonight Show" in order to replace him with rising star Jimmy Fallon. The move is believed to be fueled by competition here at ABC, with Jimmy Kimmel pulling in more viewers. A Leno rep is quoted as saying "we do not speculate on rumor." Image credit: Jason LaVeris/FilmMagic/Getty Images The wildly popular television show "Downton Abbey" is drawing both cheers and jeers from fans with the announcement that Shirley MacLaine will return in season four to reprise her role as the snarky Martha Levinson. And the woman that fans love to hate, the nefarious ladies" maid Sarah O'Brien, won't be coming back. Siobhan Finneran, whose diabolic and double-crossing character has delightfully angered millions of viewers is leaving the show for an upcoming role on the BBC. Get ready for an overdose of cuteness. The Buffalo Zoo has introduced its newest addition: a polar bear cub, barely three months old. The Buffalo News reports that she's being called "Luna" for now, but there will soon be a naming contest for her on Facebook.