It is recommended for the muezzin to turn his face to the right and left during the two hayalas, even if he is alone or for a newborn, because it is a Sunnah of the adhan in general. When he reaches the call to prayer and success, he turns his face right and left while keeping his body facing the qibla. This is because it is an address to the people, so he turns his face towards them to inform them, similar to the greeting in prayer. As narrated by Abu Juhaifa, may Allah be pleased with him, he said: 'He called the adhan, and when he reached 'Hayya 'ala as-salah, Hayya 'ala al-falah', he turned his neck right and left, but did not turn around.' This is mentioned in Sunan Abi Dawood 1:142, and he remained silent about it, and in Sunan al-Bayhaqi al-Kubra 1:395. See: Sharh al-Wiqaya p.140, and al-Durr al-Mukhtar 1:259.