Air and Water Environmental DNA Enable Detection of a Large Terrestrial Bird: A Case Study of the Southern Cassowary ( Casuarius casuarius )

ABSTRACT

The southern cassowary, Casuarius casuarius , is a large‐bodied terrestrial frugivore that plays a critical role in tropical rainforest ecosystems but can be challenging to locate and survey using traditional methods. Across much of its range, populations are threatened by habitat loss, fragmentation and other anthropogenic pressures, and key aspects of distribution and movement remain poorly understood. Environmental DNA (eDNA) offers a non‐invasive approach to monitoring elusive species, yet applications for large, mobile terrestrial vertebrates—particularly using air as a sampling medium—remain limited. Here, we develop and validate a highly sensitive, species‐specific TaqMan‐based eDNA assay to detect the southern cassowary and evaluate its performance using both air and water samples collected in captivity and in the field at sites of known presence. Cassowaries represent a biologically challenging test case for eDNA detection due to their mobility, low local densities and terrestrial ecology. Despite this, we demonstrate that eDNA from both air and water sources provides a practical, non‐invasive tool to monitor this keystone rainforest species across landscapes where traditional surveys are logistically constrained. Importantly, this approach provides a scalable method for rapidly assessing cassowary presence, supporting landscape‐scale conservation planning and management. Our results highlight the potential of airborne eDNA for detecting large terrestrial vertebrates, with broader implications for biodiversity monitoring.