I was reading various articles and care-sheets on ornates and found an interesting stat regarding their diets in the wild:

Ceratophrys ornata consumes primarily vertebrates; stomach content analysis of thirty-four specimens from Uruguay included 78.5% anurans, 11.7% passerine birds, 7.7% rodents, and 0.3% snakes, leaving only 1.8% as "other" (Basso 1990).

Frozen frogs may not be such a bad idea...