Progressive postnatal hearing development limits early parent-offspring vocal communication in the zebra finch

Acoustic communication relies critically on the receiver’s ability to hear. In precocial bird species hearing can already be functional during embryonic stages in the egg, while in altricial bird species hearing typically starts after hatching. Recent research suggests that zebra finch embryos, despite being altricial, have functional hearing already in the egg to engage in parent-embryo acoustic communication and in anthropogenic noise detection. However, their auditory sensitivity during early development remains unknown. Here, we measure auditory brainstem responses over early postnatal development and show that zebra finch hatchlings are deaf even to loud, broadband sounds with hearing responses emerging between 4-8 days after hatching. Auditory sensitivity develops progressively and reaches adult levels by day 20, contradicting the notion of early parent-to-embryo communication in zebra finches. Additionally, egg vibrations induced by sound remain far below detection thresholds of vibrotactile senses. The striking timing coincidence between maturation of the peripheral auditory system and the onset of song learning suggests that hearing functionality may gate the onset of vocal learning in zebra finches.