BCT has created an online bat sound library which features bat calls recorded from tuneable heterodyne detectors. It is an ongoing project which aims to provide recordings of all UK bat species, illustrating the differences and similarities between different species' calls and how they vary in different habitats. It's a great way to brush up on your ID skills and to help train your ear for species counted in the NBMP surveys.
This resource is exclusively for BCT Members and National Bat Monitoring Programe (NBMP) volunteers. Unfortunately these pages aren't ready yet. We are working very hard to have these up and running soon.