My baby Zebra keeps opening and closing her/his beak, and won't chirp?!?

My baby Zebra Finch we have been hand-feeding her for 2 days now as the parents abandoned her/him. Though usally she is chirping but I thought that when u give them food then they chrip but before feeding and after feeding all she does is open her beak and close her. Is she/he just tired after eating? Is something wrong with her/him?