I didn't read any of these, so I can't give you details, but fwiw, right after our ds read Percy Jackson he read the Warriors series (about a cat society) and then the Guardians of the Ga'hoole series (about owls). I don't know if they were scary or not, and ds isn't here right now so I can't ask him - but I do vaguely ds talking about an evil owl who pushed his own brother out of the nest (I think - my memory isn't all that great!). They may not be exactly what you're looking for, but ds *loved* them all, as well as the other Riordan series.
polarbear
