Cataloging frogs calls are a robust method of collecting data for bullfrog immigration, but they don't work year round, are subjective and need dedicated volunteers. eDNA needs specialists and resources. The early methods of airguns for sample collecting are unlikely to be approved for urban public spaces.

Fyke nets have promise, but permission to deploy them is not a given, plus costs, maintenance and perceived impact on ecosystem are problems.

Is there any method that is virtually free, quick and easy? Wondering if there is any experience of identification of species via photographs of individuals like they do for whales?