Ever heard a shrew warble? Secret sounds of small mammals revealed

Discover how bat detectors are used to capture the hypersonic world of voles, shrews and wood mice - and listen in yourself

It sounds like the alarm call of a macaque but is in fact the slowed-down squeak of a pygmy shrew. This warbling call is an insight into the hypersonic world of small mammals, which are generally very good at keeping their world secret from ours.

Ecologist Huma Pearce is listening to these unfamiliar woodland sounds on her laptop - but without a special device all she would hear would be the usual chatter of walkers, overexcited dogs and wind tickling the treetops.