Determinants of vocal variation in Australian Cuckoos

Avian brood parasites lay their eggs in other species’ nests, and host parents hatch and feed the chicks. To avoid imprinting and mating with the wrong species, brood parasites need to recognise and learn their own call. While northern hemisphere cuckoo vocalisations are well-studied, very little is known about the vocalisations of Australian cuckoo species. The aim of this research was to study Australian cuckoo vocalisations and determine what factors might be leading to differences within and between species and subspecies. To do this I used the program Raven Pro to measure the call structure of recordings from eleven cuckoo species from around Australia. I then assessed if there were any relationships between vocalisation and migration or habitat by comparing call characteristic with geographic distance and habitat structure. I found that size was a major factor in determining species call differences with a high negative correlation between sound frequency and morphological measurements of mass, wing, tarsus and bill lengths. Within species there was variation due to geographic isolation and variation in pitch and call duration attributable to the acoustic qualities of their habitat. The brood parasites’ preferred habitat was host dependant and aligned with arrival dates of migratory hosts. With about 180 host species between them covering a myriad of habitat types, Australian cuckoo presence is an excellent indicator of ecosystem health. Australian cuckoos are migratory species that call incessantly and are easily recognised on their breeding grounds, making them ideal species to monitor using modern acoustic methods. Climate change may severely affect migratory brood parasites because of their dependent ecological interactions and coevolutionary dynamics with their hosts. By using acoustics to track changes in cuckoo presence and range, ecosystem health and habitat quality can be measured and monitored in a more efficient and cost-effective manner than traditional monitoring techniques. Cuckoos are bio-indicators of a healthy ecosystem and change in migration arrival dates and length of residency, or range shift because of climate change could lead to a mismatch in breeding times for cuckoos and their hosts. This would be significant information towards conservation efforts of declining woodland species.