(no subject)
Recent research on the ultrasonic squeeks mice make suggest they are quite complex like bird songs
http://www.timesonline.co.uk/article/0,,11069-1851732,00.html
http://www.eurekalert.org/pub_releases/2005-10/plos-mha102605.php
Here is a company making the equipment they may have used to do this research:
http://www.avisoft.com/rats.htm
and off topic
a new technology to replace the computer mouse using ultrasoncs like a bat uses:
http://research.microsoft.com/displayArticle.aspx?id=309
a site showing how to enrich a captive mouse environment:
http://www.awionline.org/pubs/cq02/Cq-mice.html