Why do shrews twitter?

Shrews, along with scurrying, spend a great deal of time twittering. German scientists Bjorn M. Siemers, Grit Schauermann, HendrikTurni and Sophie von Marten tried to figure out why. For that they developed an artificial shrew:

Shrews are very vocal animals. We tested behaviourally whether the high-pitched laryngeal ‘twittering’ calls of as-yet unclear function serve for communication or echo-based orientation. […] To assess the acoustic feasibility of shrew echo orientation, we ensonified shrew habitats in the field with an ‘artificial shrew’ (small speaker mounted close to a sensitive microphone). The data showed that shrew-like calls can indeed yield echo scenes useful for habitat assessment at close range.

As the presence of other shrews did not elicit a significant change in twitter rate, they concluded that shrews were not using twitters to get in touch with each other – as online human tweeters do.