nicki_minaj_web.jpgLOS ANGELES (AP) — In the heyday of American Idol, the notion that it could lose ratings to a zombie slugfest or standard crime drama would have been laughable.

That was then. With Fox’s singing contest shedding about 20 percent of its audience so far this season to hit new lows, it’s been leapfrogged repeatedly in total viewers by series like CBS’ Person of Interest and NCIS.

In a harsher blow to a blockbuster that once ruled the advertiser-adored young adult segment, Idol has been overtaken this season by AMC’s The Walki-ng Dead, despite the addition of glossy new Idol judges Mariah Carey, Nicki Minaj and Keith Urban.

But in its 12th season, American Idol is managing to hit the right notes with sponsors if not always with fickle viewers: It has kept its status as TV’s advertising leader among series and the loyalty of its biggest backers, including Ford and Coca-Cola.