Third person plural, present indicative active, of the verb ἐπῳάζω (cf. epsilon 2828), evidently quoted from somewhere (perhaps Aristotle, Historia Animalium, where it occurs six times). Hesychius glosses ἐπι τοῖς ᾠοῖς βοῶσιν , "they call out over their eggs." Perhaps there is some confusion between this verb and ἐπαείδω "I sing over."
At alpha 1114 (Aelian fr. 196 Hercher), it appears that the hens would sing out when their eggs are stolen.