Trill Song (audio) University of Melbourne Loading audio... Caption This is an example of a trill song type that tells listeners how big the singer is. Their larger physical size means that bigger male purple-crowned fairy-wrens can sing this trill song type at a lower pitch than smaller males can. Credit Michelle L Hall Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.