Ululatus - defined in "The new college Latin and English Dictionary" as howling (of dogs and wolves), wailing(mourning), war cry. 2. Howl out, howl at, wail. To me since ulula -ae is owl, I assume a more accurate definition would be night howls. The root and words built on it appear to be mainly for creatures that howl, wail, or cry after dark. To answer more specifically your question, my hypothesis would be that ulula is the diminutive of ululatus, the most commonly and regularly heard creature of the night. I've not generally seen this word used for mourning, only referring to a nocturnal activity.