Young rhea chicks employ several context-specific calls, but lose most vocal capabilities by the age of seven weeks. As the trachea grows, the internal tympanic membranes intrude less into the bronchial passages, contributing to the deterioration and ultimate silencing of the adult rhea's voice (Beaver 1978).
Adult rheas are mostly silent. During breeding the male gives a low-pitched, two noted boom or roar, which can be heard for up to 1 km (Sick 1993). An alarm call is a "hoarse grunt" (Sick 1993).
For a representative audio recording with sonogram, see audio