Actually I researched it a few years ago. Titmouse comes from the Old English "tit", which means "little", and the proto-Germanic "mause" which means "bird", so it would seem that the plural would be Titmouses......unless you go with the German plural. Then it would be "Titmousen". But it seems that either titmice OR titmouses is the correct plural form, so either one is acceptable.
Kingdoms RAGE and go to war...but the PEasants plant potatoes..
EARTH FIRST! (we'll strip-mine the OTHER planets later.)